Tuesday, May 8, 2012

Prostate Cancer Stem Cells

There has been a great deal of work on stem cells (see our White Paper). We may think of such cells as being part of the embryo, and in the placenta at birth. They are thought of as the universal cell generator. Theoretically the stem cell should become whatever cell type we may want it to be. In a more narrow sense there may be a variety of localized stem cells, namely cells which replenish local cells which are worn away such as on the skin or in the colon. It is not the mature cells which do the reproducing but it is the few stem cells which reside in say the basal layer of the skin which reproduce and create off spring which are just plain old keratinocytes.

In this note we examine in some detail the prostate stem cell, and in turn we generate the ability to consider the cancer stem cell issue in broader detail. We have discussed this issue in our draft volume on Prostate Cancer Genomics, and this is an additive section as that volume progresses.

The focus is on stem cells. It does not address the pathways which are different or activated. That in itself is a critical question. Namely what differentiates a stem cell from a mature non stem like cell when we examine the pathways? Thus when looking at PCa we see that pathway changes are then most likely pathway changes in the stem cell alone, yet if the agglomeration of stem cells is such that the non-stem constituents reflect the genetic makeup of the stem cell, then we would expect some parity in pathway dynamics. This will be an issue we examine in a later report.

The cancer stem cell theory has been developed over the past decade or so. For many years the theory was that cancer was clonal, namely one single cell was at fault and its progeny were the direct result of that genetically modified parent, a single parent, and that as the cancer evolved there may be increased genetic defects but again all were from a single parent.

Cancer stems cells are a construct which predicates the development of mature cells in a cell line as coming from a set of stem cells, akin to the blood cells arising from the bone. In contrast to the linear model of Vogelstein, say in the colon, the epithelial cell of the colon wall has some genetic disruption, and after multiple disruptions this epithelial cell becomes cancerous, dividing without bounds and failing to remain where is was supposed to. Typically an adenoma develops which after the final genetic hit becomes an adenocarcinoma.

For example, we have examined the prostate cancer cell, and in so doing have used a non CSC model, namely it is a basal or luminal cell which becomes genetically changed. If however we are wrong and there is an equivalent prostate cancer stem cell, as some have conjectured, then management of cancer of the prostate is quite a different thing. As we have expressed before, if one has diffuse HGPIN in the prostate and then after several high density prostate biopsies it disappears, is that inferentially valid for a prostate CSC?

The cancer stem cell construct is fundamentally different. It is not a mature cell which takes the genetic hits but the stem cell. The malignant stem cell acts almost as a force at a distance, and can impact other cells as the stem cell itself can reproduce, albeit at a somewhat slower rate than what it may influence.

Arguably if one can remove the stem cell then one removes any future malignancy, even to the extent of having other cells enter apoptosis for failure of having an active stem cell.

As Weinberg notes, there is the theory of clonal development of cancer which states that the cancer cells are pluripotent and have developed from a single source and that they have the capability of reproducing and do so in an autonomous manner[1]. Then there is the theory of the cancer stem cell, the theory which states that there is the equivalent of a stem cell as we know in blood cells, which have the capability but that the majority of malignant cells do not necessarily have that capacity.

The NCI presents an excellent summary of Cancer stem cell, CSC, research[2]:

The theory of the cancer stem cell (CSC) has generated as much excitement and optimism as perhaps any area of cancer research over the last decade. Biologically, the theory goes, these cells are distinct from the other cells that form the bulk of a tumor in that they can self-perpetuate and produce progenitor cells, the way that traditional stem cells do. The progenitors’ job is then to repopulate tumor cells eradicated by treatments such as chemotherapy or radiation.

But for all the attention and fanfare CSC research has received, the findings reported to date are far from clear-cut, investigators acknowledge. For example, most of the studies that have identified human CSCs have used mouse xenograft assays and cells from only a small number of human tumor samples, making it difficult to draw firm conclusions. In addition, other researchers haven’t always been able to replicate initially reported findings. And while these tumor-initiating cells, as they are also called, have been described as being a rare class, several studies have found that the number of cells that can form tumors in these mouse experiments is actually quite large, suggesting that perhaps CSCs aren’t such a privileged breed.

As we shall discuss herein, the CSC does not yet have a steady state definition or description. Furthermore it is also difficult to tag and identify. In the above definition, there is the issue of what makes the stem cell different and how many are there and how do we identify it. The CSC is in one sense the single cell which can regenerate a full cancer growth. But does that mean in vivo or in vitro or both? Murine models have been used extensively but there are serious questions regarding their extensibility.

We shall discuss some of these issues in this report. Now the NCI goes on to say:

In other words, the idea of just what cancer stem cells are, and their role in different cancers, appears to be changing.

“The [stem cell] model has not been adequately tested in most cancers,” said Dr. Sean Morrison, who directs the Center for Stem Cell Biology at the University of Michigan. “I think that there are some cancers that do clearly follow a cancer stem cell model…But it will be more complicated than what’s been presented so far.”

They continue by noting a significant conclusion of the CSC theory, the fact that the CSC is the controlling cell, not just any cell. Specifically they state:

Unlike the random or “stochastic” model dominant in cancer research, which holds that nearly any cancer cell has the potential to form a tumor, the cancer stem cell model is one of a hierarchical organization, with the pluripotent cancer stem cell sitting ready and able to amass all of the components of the original tumor.

It’s also thought, with some experimental evidence to support it, that CSC pluripotency allows these cells to adapt and to resist chemotherapy, radiation therapy, and even current molecularly targeted therapies. If true, then these treatments may not harm the most lethal tumor cells, those that can lead to a recurrence with the production of a new set of progenitors.

Despite numerous studies published in the last 16 years that identified CSCs for different cancers—including colon, brain, pancreatic, and breast cancer—the consensus among researchers seems to be that the evidence is strongest for the first cancer in which a population of tumor-initiating cells was discovered, acute myeloid leukemia (AML), as well as for other blood cancers.

The above has substantial positive and negative impact. A single stem cell may control everything, for a while. If however it undergoes mitosis then we may have many stem cells. Or we may keep a single one. For example if a stem cell in mitosis reproduces a single stem cell plus a non-stem cancer cell, then we maintain single CSCs, while we multiply the malignant non CSC cells. However, if the CSC in mitosis just multiples itself for a while, then we end up with a collection of very powerful and spreadable bombs of CSCs.

The NCI also continues:

 “The reason why it’s so much stronger for hematologic malignancies are because hematopoiesis research goes back 40 or 50 years and it’s very stem cell-based,” said Dr. Jean Wang, a stem cell researcher at the University of Toronto. “Whereas in solid tumors, there’s less of a foundation for identifying the normal cellular hierarchies and for [cell-surface] markers that identify different populations of cells like stem cells and progenitors.”

The above comment has some merit but one must also recognize that the hematopoietic cells are fundamentally generated in a specific location, the bone, and there may very well be no such locations specificity for the many other cells we are considering. Nevertheless, we continue:

Even so, Dr. Wang believes the existence of CSCs is pretty well demonstrated for breast and brain cancers. But, she cautioned, “I don’t know if it applies to all cancers. In a lot [of cancers] it does seem to apply. But most of the markers we have right now are still very rough.”
Despite the evidence for CSC-like cells in a growing number of cancers, the theory clearly has its skeptics, who point to problems such as shortcomings in the mouse xenograft assay and the variable specificity of the cell-surface markers used to demarcate a CSC from a non-CSC.

“I still feel that it’s a concept yet to be proven,” said Dr. Barbara Vonderhaar, who, along with colleagues in NCI’s Center for Cancer Research, recently published a study identifying a population of CSC-like cells in estrogen receptor-negative breast cancer. “It’s certainly a good idea, but it’s only a hypothesis at this point. We still don’t have definitive proof that cancer stem cells exist.”

The CSC concept is “a work in transition,” said Dr. William Matsui, from the Johns Hopkins School of Medicine, whose lab studies the role of stem cells in hematologic cancers. “To me, as a clinical person, the ideal model is one where you can find something that is going to work in humans. We’re far from that.”

The existence of CSCs in PCa has been examined and as with many cancers is still open for discussion. However as we shall discuss later the CSC model does have certain interesting uses in the progression and metastasis of cancer.

For example:

Cell Proliferation: If we assume that the CSC is the dominant cell that proliferates and all others do not, albeit being cancer cells themselves, then the growth of PCa in terms of cells is complex but one can then more easily explain indolent PCa.

Metastasis: We know that metastasis occurred by lymphatic and hematological means. However PCa cells, non-CSC PCa cells may break loose and yet not result in classic metastasis. The issue then is one where it may be necessary for the CSC to move by these means.

Many other such issues will arise and we discuss the CSC idea here and we return to it later in the work.

Now we can view the stem cells as shown below. There is a stem cell which can give rise to a new stem cell of ultimately a Post Mitotic Differentiated Cancer Cell. The PMDC cannot replicate, whereas the stem cell can. For metastasis it is thus necessary to send out a few stem cells, not PMDC cells.

The first issue is a definition of a stem cell. We may understand stem cell from the hematopoietic stem cells found in the bone which give rise to a variety of blood cells and other types of cells. In fact almost all cells in the body which require some form of replenishment have such stem cells. Consider the skin. The basal layer has stem cells to generate the keratinocytes. In fact it may be argued that melanocytes have their own stem cells as well.

Cells are reproducing via the cell cycle as we show below and discuss in Appendix B. With a stem cell, it is only that cell which does the mitotic division; all other cells are just mature functioning cells subject to normal cell death or apoptosis.

The question is however, which cells. Which cells are the stem cells? Are all cells reproducing or just some select class of cells. The concept of stem cells makes the issue one of a small select group of cells. These are the stem cells.

As Alberts et al state (pp 1417-1421):

Humans renew the outer layers of their epidermis a thousand times over in the course of a lifetime. In the basal layer, there have to be cells that can remain undifferentiated and carry on dividing for this whole period, continually throwing off descendants that commit to differentiation, leave the basal layer, and are eventually discarded.

The process can be maintained only if the basal cell population is self-renewing. It must therefore contain some cells that generate a mixture of progeny, including daughters that remain undifferentiated like their parent, as well as daughters that differentiate. Cells with this property are called stem cells.

They have so important a role in such a variety of tissues that it is useful to have a formal definition. The defining properties of a stem cell are as follows:

1. It is not itself terminally differentiated (that is, it is not at the end of a pathway of differentiation).

2. It can divide without limit (or at least for the lifetime of the animal).

3. When it divides, each daughter has a choice: it can either remain a stem cell, or it can embark on a course that commits it to terminal differentiation.

Stem cells are required wherever there is a recurring need to replace differentiated cells that cannot themselves divide. The stem cell itself has to be able to divide—that is part of the definition—but it should be noted that it does not necessarily have to divide rapidly; in fact, stem cells usually divide at a relatively slow rate.

We present below a simplified example of a specialized stem cell. The stem cell is the only one of its kind to divide. The mature cells do not generally divide; they are just functional and proceed to mature. The stem cell always produces at least one of its own kinds, another stem cell, and then one of the mature like cells. Note the initial stem cell. In this example we allow it to divide and produce one stem cell and one maturing cell. Thus at some point this process just keeps the number of stem cells constant but can produce an ever growing number of maturing cells.

Now when we examine the above we can see that if the stem cell divides once every hour, and the life of a mature cell is say 24 hours, then we have a growth effect. We must have a cell stability of one replenishment per one destroyed. During a growth state however, the stem cells are reproducing quickly and cells are added. The stem cell responds to surface stimulants to enter into cell cycle production.

As Tang et al state:

Normal adult stem cells (SC) have several fundamental properties: they are generally very rare, can self-renew, have tremendous proliferative potential but normally (i.e., in their niches) are quiescent, and can differentiate along one or several different cell lineages.

The most defining property of a SC is its ability to self-renew while being able to differentiate into all different lineages of progeny and even to reconstitute an organ, as exemplified by a single hematopoietic SC (HSC) to reconstitute the whole blood and rescue an irradiated mouse. SC development is a continuous and dynamic process, in which cells with distinct self-renewal, proliferative, and differentiation abilities may co-exist.

For example, mouse HSC are heterogeneous populations of cells containing long-term HSC (LT-HSC), which can sustain life-long self-renewal and reconstitution, and short-term HSC (ST-HSC), which can sustain self-renewal and reconstitution for only 8 wk. The ST-HSC generate multi-potent progenitor (MPP) cells exhibiting only limited self-renewal capacity, which then further develop into lineage-restricted progenitor (or precursor) cells that have lost self-renewal ability.

Although this paradigm of LT-HSCST-HSC early progenitors (MPP) late progenitors differentiated cells in mouse bone marrow can, in principle, be applied to other SC developmental processes, in reality, little is known about most tissue SC lineages and we often name the subsets of cells in a specific tissue/organ with certain self-renewal and differentiation abilities simply stem/progenitor cells. Such is the case with the putative prostate epithelial stem and progenitor cells.

Consequently, throughout this review, we shall frequently use the term ‘(prostate) stem/ progenitor cells.’

The above feature of maturing into various lineages is clearly seen in blood cells but one may question just where it functions say in prostate cells. Is there a single stem cell which generates either a basal or luminal cell or if so where does it reside, and how does this differentiation occur? This is the point made by Tang et al towards the end of the above quote.

Cancer stem cells are a variant of the benign stem cell. Namely a cancer stem cell is a cell which behaves like a stem cell in terms of cell proliferation but now has genetic changes which reflect malignant behavior. In an NIH report the authors define cancer stem cells as follows:

A consensus panel convened by the American Association of Cancer Research has defined a CSC as "a cell within a tumor that possesses the capacity to self-renew and to cause the heterogeneous lineages of cancer cells that comprise the tumor." It should be noted that this definition does not indicate the source of these cells—these tumor-forming cells could hypothetically originate from stem, progenitor, or differentiated cells.

As such, the terms "tumor-initiating cell" or "cancer-initiating cell" are sometimes used instead of "cancer stem cell" to avoid confusion. Tumors originate from the transformation of normal cells through the accumulation of genetic modifications, but it has not been established unequivocally that stem cells are the origin of all CSCs.

The CSC hypothesis therefore does not imply that cancer is always caused by stem cells or that the potential application of stem cells to treat conditions such as heart disease or diabetes, as discussed in other chapters of this report, will result in tumor formation. Rather, tumor-initiating cells possess stem-like characteristics to a degree sufficient to warrant the comparison with stem cells; the observed experimental and clinical behaviors of metastatic cancer cells are highly reminiscent of the classical properties of stem cells.

The stem cell theory, and there seems now to be significant evidence of its validity in prostate cancer, is principally that the clonal theory has merit to a point but that the development is more complex and the cancer stem cell plays a critical role in fostering growth of the cancer cells, most of which has less aggressive a growth characteristic if any at all.

Lawson and Witte present a recent overview of this concept as applied to the prostate and PCa. Recent studies apparently indicate that the cancer stem cells, CSC, are necessary to sustain later stages of the development of the malignancy. Only a small subpopulation of the cancer cells, the CSC population, has a demonstrated ability to maintain the malignancy as well. Lawson and Witte present two theories of this CSC process. One is called the stochastic theory which is that all cells are equally malignant. The other theory, the one for CSC, called the hierarchical theory is that only the CSC has the ability to multiply.

The CSC or in this case the PSC, prostate stem cell, yields a TAC, or transition amplifying cells, then yield progenitor cells, LP or BP, and then finally a luminal or basal cell. This is slight contrast to the Goldstein model. This model applies for both benign as well as cancer cells, at least as viewed by Lawson and Witte.

Now if one looks at the CSC theory, then we see a CSC has progeny, and yet those progeny may not have the ability to multiply. Thus the explosive exponential growth of cancer is not as clear in a CSC model, because almost all of the progeny of the CSC are no reproducing progeny. Thus the growth models for a CSC based malignancy are more complex and are dependent on limited CSC reproduction and non-CSC reproduction. However the CSC model also argues for there being some CSC support for the progeny which are not CSC. The dynamics of cell growth then becomes quite complex here, for the stem cells replicate themselves at a slow rate but are replicating other cells at a higher rate. However the other cells do not replicate themselves they just go through a standard cell process. If the cells are benign then they go through apoptosis as seen in red blood cells and the skin keratinocytes.

We quote Lawson and Witte as follows:

Models of prostate epithelial differentiation. The traditional model for prostate epithelial differentiation proposes that PSCs residing in the basal cell layer give rise to intermediate, transit-amplifying cells that produce large numbers of terminally differentiated secretory luminal cells …. This model implies a linear differentiation scheme in which basal and luminal cells comprise one lineage and basal cells are essentially luminal cell progenitors …

This hypothesis is supported by the existence of cells of intermediate phenotype that express both basal- and luminal cell–specific cytokeratins in both fetal and adult stages of prostate development … Intermediate cells can also be identified in in vitro cultures of primary prostate epithelium … Several studies have also suggested basal cells can differentiate into luminal cells in vitro … Alternative theories for prostate epithelial differentiation propose basal and luminal cells may represent separate epithelial lineages … This is similar to prevailing models for epithelial differentiation in the mammary gland, a tissue that is anatomically and functionally analogous to the prostate …

Now there have been several others who have examined the stem cell model for PCa. Another of recent merit is that of Hurt et al. They summarize their work as follows:

Recent evidence supports the hypothesis that cancer stem cells are responsible for tumor initiation and formation. Using flow cytometry, we isolated a population of CD44+CD24- prostate cells that display stem cell characteristics as well as gene expression patterns that predict overall survival in prostate cancer patients. CD44+CD24- cells form colonies in soft agar and form tumours in NOD/SCID mice when as few as 100 cells are injected.

Furthermore, CD44+CD24- cells express genes known to be important in stem cell maintenance, such as BMI-1 and Oct-3/4. Moreover, we can maintain CD44+CD24- prostate stem-like cells as non-adherent spheres in serum-replacement media without substantially shifting gene expression. Addition of serum results in adherence to plastic and shifts gene expression patterns to resemble the differentiated parental cells.

Thus, we propose that CD44+CD24- prostate cells are stem-like cells responsible for tumor initiation and we provide a genomic definition of these cells and the differentiated cells they give rise to. Furthermore, gene expression patterns of CD44+CD24- cells have a genomic signature that is predictive of poor patient prognosis. Therefore, CD44+CD24- LNCaP prostate cells offer an attractive model system to both explore the biology important to the maintenance and differentiation of prostate cancer stem cells as well as to develop the therapeutics, as the gene expression pattern in these cells is consistent with poor survival in prostate cancer patients.

Jordan et al characterize cancer stem cells as having three characteristics:

1. Self-Renewal: at the end of mitosis of the stem cell, either one or both retain all the characteristics of the parent. The stem cell goes through a mitotic doubling and when it does it always retains one or two stem cell daughters.

2. Capability to generate multiple lineages. This means that a stem cell can generate offspring which can become anyone of many cell types.

3. Potential to proliferate extensively. The cell can keep replicating, it has no limitation within reason and thus contains the elements ultimately for metastasis.

A normal stem cell may mutate to a cancer stem cell or a normal progenitor cell may morph back to a cancer stem cell.

As Delarbra et al state:

Although monoclonal in origin, most tumors appear to contain a heterogeneous population of cancer cells. This observation is traditionally explained by postulating variations in tumor microenvironment and coexistence of multiple genetic subclones, created by progressive and divergent accumulation of independent somatic mutations.

An additional explanation, however, envisages human tumors not as mere monoclonal expansions of transformed cells, but rather as complex tridimensional tissues where cancer cells become functionally heterogeneous as a result of differentiation.

According to this second scenario, tumors act as caricatures of their corresponding normal tissues and are sustained in their growth by a pathological counterpart of normal adult stem cells, cancer stem cells.

The statement starts with the accepted monoclonal hypothesis and then departs to a polyclonal alternative view. It retains the CSC, cancer stem cell, paradigm for solid tumors as well. In the context of HGPIN we see a change in the cells and we have heard the argument that they have made one or several of the unchangeable steps towards PCa. Thus using the CSC theory one would expect that it would be from one or several of these cells that PCa would arise. In addition, we could assume that there is no unique pathway mutations or changes which result in PCa but a plethora of them. Simply stated, cancer is complex, it finds ways to migrate forward no matter what the path.

The statement starts with the accepted monoclonal hypothesis and then departs to a polyclonal alternative view. It retains the CSC, cancer stem cell, paradigm for solid tumors as well. In the context of HGPIN we see a change in the cells and we have heard the argument that they have made one or several of the unchangeable steps towards PCa. 

Thus using the CSC theory one would expect that it would be from one or several of these cells that PCa would arise. In addition, we could assume that there is no unique pathway mutations or changes which result in PCa but a plethora of them. Simply stated, cancer is complex, it finds ways to migrate forward no matter what the path.

A recent study by Deleyrolle et al has focused on the stem cell and its dynamics[3]. The reviewers state:

The method, published in the online journal PLoS ONE in January, may rev up efforts to develop stem cell therapies for Alzheimer's, Parkinson's and other diseases. It may also help get to the root of the cancer-stem cell theory, which puts forth the idea that a tiny percentage of loner cancer cells gives rise to tumors.

"Math is going to be the new microscope of the 21st century because it is going to allow us to see things in biology that we cannot see any other way," said Brent Reynolds, Ph.D., an associate professor of neurosurgery at UF's McKnight Brain Institute and a member of the UF Shands Cancer Center. "Stem cells and the cells that drive cancer may be as infrequent as one in 10,000 or one in 100,000 cells. The problem is how do you understand the biology of something whose frequency is so low?"

Inspired by a 2004 essay by Joel E. Cohen, Ph.D., of The Rockefeller University and Columbia University that described the explosive synergy between mathematics and biology, Reynolds and postdoctoral associate Loic P. Deleyrolle set out to build an algorithm that could determine the rate stem cells and cancer stem cells divide.

High hopes to treat or prevent diseases have been pinned on these indistinguishable cells, which are often adrift in populations of millions of other cells. Scientists know stem cells exist mainly because their handiwork is everywhere — tissues heal and regenerate because of stem cells, and somehow cancer may reappear years after it was thought to be completely eliminated.

Nature has an interesting poster on the cancer stem cell, CSC[4]. The poster states:

The concept of the cancer stem cell (CSC) has taken off rapidly over the past 10 years. CSCs are cells with properties that are similar to those described for tissue stem cells: self-renewal and asymmetric division resulting in the generation of daughter cells destined to differentiate, enabling the regeneration of a tissue. Initial research into the properties of CSCs was based on identifying and verifying markers of this subset of cancer cells.

However, most studies have now moved on to understanding the biology of CSCs and the cancers in which they maintain tumour growth, as well as how and why they are able to serially generate a tumour. It is thought that a key element regulating the biology of stem cells is their niche — cells and extracellular matrix that support self-renewal and survival. As we begin to understand the pathways that are crucial for the properties of CSCs, including signals provided by the niche, we will hopefully be able to effectively target this cell population.

Linked to the identification of CSCs is the cell of origin. These are cells that when mutated are able to give rise to a tumour. Although these cells may share properties with CSCs, in most cases it is not yet clear whether these cells are one and the same. This poster highlights some of the recent findings regarding the biology of CSCs and the identification of cell types from which cancers can arise. 

As regards to prostate cancer they state:

In the normal prostate, epithelial cells with tissue-regenerating capacity that are Sca1+, CD49fhi, TROP2hi, CD44+, CD133+ and CD117+ (mouse) or CD133+, CD44+, CD49fhi and TROP2+ (human) seem to reside in the basal layer of the prostate. However, studies in mice indicate the existence of luminal cells with progenitor characteristics that can regenerate the prostate after androgen withdrawal. As castration resistance is also a property of basal stem cells in the prostate, it suggests a complex cellular hierarchy.

Studies in mice indicate that prostate tumours can arise after transformation of basal stem cells and luminal progenitor cells. A subset of cells that are CD133+, a2b1 + and CD44+ and have basal cell characteristics have been shown to be tumorigenic, but whether these cells can serially propagate tumours in mice has yet to be verified.

Again and interesting experiment can be performed:

1. Take biopsies from N men with HGPIN diagnosed on initial biopsies. Perform sampling from say 20 cores.

2. Wait 9 months, and rebiopsy, again with near saturation cores, 20+ .. There are three possible outcomes:

a. HGPIN remains
b. PCa has been determined
c. HGPIN regresses and only benign cells are left

3. The question is why did (c) above happen? What percent of the HGPIN have regressed? If the percent of HGPIN that have regressed equals the probability of having actually excised the cancer stem cell or cells, we can calculate this, then by chance we have removed the CSC from the HGPIN and this would affirm its existence by inference.

Now a similar article appears in Science which speaks to colon cancer and the cancer stem cell theory[5]:

In normal colon tissue, intestinal stem cells (ISCs) that reside at the base of mucosal wells, named crypts, expand through mitosis and move upward toward the crypt tip. The cells then undergo cell cycle arrest and terminal differentiation, finally becoming the mucosal epithelium of the colon. In the recent study, the investigators identified in mouse ISCs a gene signature that was specifically marked by high expression of the ephrin type-B receptor 2 gene(Ephb2), which encodes a receptor tyrosine kinase, the leucine-rich repeat–containing G protein–coupled receptor 5 gene (Lgr5), which encodes a G-coupled protein receptor of unknown function, and ~50 other genes.

This gene signature also defined a specific population of stem-like cells at the base of colorectal tumor structures in mice that were morphologically similar to normal mouse intestinal crypts. The authors then similarly inspected tumor samples from 340 colorectal patients and discovered a 10-fold increase in the relative risk of recurrence in patients whose tumors displayed high expression of the human counterparts of the mouse ISC genes, relative to patients whose tumors showed low expression of these genes. 

To test whether the mouse colorectal tumor cells with the ISC gene signature were cancer stem cells; the investigators isolated the cells and introduced them into an immunodeficient mouse model. The stem-like cancer cells demonstrated both a tumor-initiating capacity and self-renewal capability in vivo.

These findings pinpoint potential markers that may allow a clinician to predict a patient’s future with respect to recurrence. These differentially expressed genes also may give rise to therapeutic targets that quell cancer stem cells. 

What is clear is that the CSC is becoming a viable model for understanding cancer at another level.

We first relook at the progression and regression dynamics. The key driver for the analysis herein has been the regression often seen in HGPIN. Knowing that most likely the methylation of GSTP1 has given rise to development of PIN we then ask what gives rise to its regression and why have the HGPIN cells themselves not only stopped growing but have disappeared. Again we have seen this in melanomas, and this is also the Rosenberg effect in certain sporadic cancer regressions.

To look more closely we first return to the stem cell model for cancer which we developed earlier. The stem cell theory states that there are a certain number of cancer stem cells which in turn may replicate themselves but also create what are termed post mitotic differentiated cells. Not really stem cells but cells which exhibit the phenotypic characteristics of a cancer cell. One of the questions one may pose is do these PMDC exhibit a different genotypic character as well or are they controlled by some epigenetic factors.

Now we can also see as Weinberg has noted (Weinberg p 419) that a progression may occur in a somewhat more complex mechanism as we depict below. Now from the stem cell arises Transit Amplifying Cells and then the PMDC.

Now in reality there may be multiple genetic hits which give rise to the stem cell, the pluripotent self-replicating core of a cancer. The Figure below provides a generic profile, namely we may see many genetic changes, some leading to cancer as in mutation 3 below and others just wandering off into self-replicating cells but not with a malignant tendency.

Finally when we return to the HGPIN model we see the benign cell migrating to a dysplasia, say HGPIN, and then to a malignant cell, but then there is the regression back to a benign cell. The question is then; what pathway elements takes us one way and what elements take us back. And what happened to the dysplastic cells? Did they just die, apoptosis, or were they scavenged?

Wang and Shen have written a quite useful review of the cancer stem cell thesis for prostate cancer. There is no definitive conclusion but the review covers a wide path through what has been accomplished to date.

Recall as we have written before the cancer stem cell (CSC) model, and it is a model, hypothesizes that there are certain core cells which control the malignant growth of other cells and that the other cancerous type cells do not in and of themselves have the ability to continue to grow. In fact it could be concluded, although not part of the current theory, that removal of a CSC from a tumor, say the only CSC, would result in the apoptosis of the remaining cells. Namely, a remission.

In contrast to the CSC model we have the clonal model which says that the cells have progressed through a set of pathway modifications that have resulted in a single cell which takes off and multiples and that the progeny have identical genetic makeup or further genetically modified makeup but all and equally malignant.

These are two fundamentally different views of cancer. One could also state that recent work with melanoma as we have discussed also posit that the CSC “communicates” to progeny to have them multiply and that arguably the loss of the CSC

There is a great deal of difficulty in identifying the CSC, usually attempting to do so via surface markers such as CD44 and the like.

Wang and Shen then discuss the controversy regarding the CSC concept. They state:

Much of the confusion in the literature arises through inconsistencies in nomenclature within the field. In particular, due to the wide use of xenotransplantation as a functional assay for CSCs, transformed cells that can initiate tumor formation in this assay are often referred to as CSCs in the literature. However, a tumor initiating cell (TIC) represents a different concept from that of a CSC, as TICs unquestionably exist within tumors and their identification does not by itself imply a hierarchical organization of a tumor.

Indeed, the majority of cells within a tumor could potentially possess TIC properties and nonetheless follow a clonal evolution model. Consequently, it is important to distinguish CSCs that have been strictly defined by their position and function within a lineage hierarchy in vivo from CSCs that have been identified as rare TICs in transplantation studies.

A similar confusion arises with respect to the cell of origin for cancer, which corresponds to a normal tissue cell that is the target for the initiating events of tumorigenesis. In principle, a normal adult stem cell could be a logical cell of origin for cancer, as it would retain the ability to self-renew and generate a hierarchy of differentiated lineages within a tumor. However, it is also possible that a cell of origin could correspond to a downstream progenitor cell or conceivably even a terminally differentiated cell that acquires stem cell properties during oncogenic transformation.

Our argument has been that the CSC may most likely exist and that it has undergone certain pathway changes and that as a result it may influence the growth of not identically genetically changed cells to multiply but not in and of themselves have the potential to multiply.

Wang and Shen continue:

The identification of normal cells that can serve as a cell of origin for prostate cancer is highly relevant for understanding the applicability of a CSC model, and is currently under intense investigation. The cell of origin may also have clinical significance, as in the case of breast cancer, distinct tumor subtypes have been proposed to originate through transformation of different progenitors within the mammary epithelial lineage. Thus, it is conceivable that there may be distinct cells of origin for other epithelial cancers, and different cells of origin may give rise to clinically relevant subtypes that differ in their prognosis and treatment outcome.

Thus there are either basal cells or luminal cells as the cell of origin. Goldstein et al in Witte’s lab had developed a murine model demonstrating the basal cell as the cell of origin. However there may be strong issue regarding this model as applied to human prostate cancer. It represents a viable pathway but not necessarily the only. The issue is one of pathways as well as one of intercellular communications with debilitated pathways.

Now to follow the Wang and Shen model we have the following. Fist we show a normal prostate gland with basal and luminal cells.

Then we show their view of a Tumor Initiating Cell in either the basal or luminal layer. The Goldstein et al murine model argue for the basal layer and there are others arguing for the luminal.

The Wang and Shen model is as follows.

1. A normal prostate cell has both luminal and basal cells.

2. TICs may be formed in either basal or luminal cells.

3. Neoplasia starts with intro acinar proliferation.

 4. Carcinoma starts when it expands beyond the gland and starts up its own quasi-glandular structures.

 Now what causes this? Genetic changes result in pathway changes. We show two pathways below. We lose PTEN and we may activate myc and other parts of the pathway control mechanism.

We now make a different argument. If there exists a true PCa CSC then perhaps one may putatively validate it as follows. The logic then is:

1. Assume a PCa CSC exists.

2. Assume that the PCa CSC replicates its CSC self at a low rate and is initially confined to the prostate gland.

3. Assume that the PCa CSC can influence the growth of TIC which themselves cannot sustain a malignancy. Specifically we assume that the TICs require the CSC for continued growth and further the CSC does so via cell growth as well as intercellular communications.

4. Now let us assume we have performed an 18 core biopsy on a 60 cc prostate gland and find histologically extensive high grade focal prostatic intraepithelial neoplasia. According to Wang and Shen they are most likely TICs and furthermore there may be a CSC somewhere so that eventually we see a PCa. There may be one or a few CSC in one or all of the glands yet we have no definitive marker to indicate as such.

5. Now assume we perform a second multi core biopsy on the gland and say do 22 cores in a 60 cc gland. This is the same gland but say 9 months later. We would arguably expect one of two possible outcomes. First that the HGPIN remains in place and possibly has expanded. Second that there was a CSC and the HGPIN had become classic PCa with say Gleason 2 or 3 at a minimum about the HGPIN clusters. 

 6. If however, we examine the cores and find no evidence of any neoplasia or PCa, namely the gland has totally reverted to benign histology, we may have a reasonable argument that perhaps the CSC was present initially, and it was somehow removed along with the HGPIN in the initial biopsy leaving the TIC alone behind. Thus the TICs requiring a CSC to survive go into an apoptotic state and are removed from the prostate. Perhaps.

We have seen that specific situation occur and one could then argue that the Wang and Shen model for CSCs may be a viable model and further if such can be shown more extensively than we may have a basis for PCa progression.

There is an interesting article by Clevers in Nature Medicine which is an up to date review of the cancer stem cell issue. In light of the flurry of reports stating the wonders of having identified genes which appear in many tumors, prostate being the case, and my previous remarks that perhaps is the CSC is in fact existent, that then one should be identifying it and its genetic makeup as well as the dynamics of its pathways.

Now Clevers suggests a four step process, albeit with limited experimental evidence, but a superb start. It is as follows:

The above are the first two steps. Perhaps a dysplasia or neoplasia but with the kernel of a stem cell. This is the first "hit" theory. The epithelium starts to grow in a strange manner. Say a polyp in the colon or HGPIN in the prostate. Then we see a second hit and the formation of extraepithelial growth.

Then the third hit for the author and we see transmission via the blood stream. Then the fourth hit and the explosion from a few to almost all cancer stem cells.

Whether this is a good or bad model is yet to be seen. As Clevers states:

Central to the cancer stem cell (CSC) concept is the observation that not all cells in tumors are equal. The CSC concept postulates that, similar to the growth of normal proliferative tissues such as bone marrow, skin or intestinal epithelium, the growth of tumors is fueled by limited numbers of dedicated stem cells that are capable of self-renewal. The bulk of a tumor consists of rapidly proliferating cells as well as postmitotic, differentiated cells. As neither of these latter two classes of cells has the capacity to self-renew, the contribution of these non-CSC tumor cells to the long-term sustenance of the tumor is negligible.

The increased focus on the CSC is truly needed because if it is indeed a key paradigm in cancer then it and not large tumor masses should be examined. Clevers concludes with:

Epilogue: are CSCs and clonal evolution mutually exclusive?

To date, the CSC field has treated tumors as genetically homogeneous entities, by and large ignoring the fact that the observed tumor heterogeneity may result from underlying genetic differences. However, it is well known that most solid tumors show extensive genomic instability. Moreover, genetic defects in a large variety of molecules that are involved in the maintenance of the integrity of the genome are well-known drivers of oncogenesis. Even in a disease like CML, so clearly driven by stem cells, clonal evolution can be seen at work when imatinib is administered: the malignancy becomes tumor-resistant through the emergence of clones that carry mutations in the target of imatinib, the BCR-ABL1 fusion gene75. And the progression of CML into ALL blast crisis is caused by the emergence of subclones that harbor inactivating lesions in the cyclin-dependent kinase inhibitor 2A (CDKN2A, also known as ARF) gene in addition to the BCR-ABL1 translocation76. The evidence for clonal evolution in the pathogenesis of cancer is so overwhelming that it appears inescapable that all models should be integrated with it.

The recent rapid advances in DNA sequencing are now allowing the global analysis of genomic changes of cancer cells. These analyses have confirmed many previously known common genetic alterations in cancer, and they have also revealed some new common mutations as well as unexpectedly large numbers of rare mutations. As a next step, this technology can be applied to chart genetic heterogeneity within individual tumors as well as between primary tumors and their local recurrences and metastases.

 It should thus be possible to map, in both space and time, the genetic evolution of a tumor.

The last sentence is the most compelling. Cancer may be more than just a cellular disease; it may require the spatial domain as well. This is an exceptionally good review and should be a focus for future research.

Recent work by Qin et al. examine the more detailed nature of the prostate cancer stem cell (PCa CSC). We here look at that as a starting point and then examine some of the surrounding literature to see if the results from that work can be extensible. The cancer stem cell model is one which akin to the stem cell model above states that there are a class of stem like cells which have been mutated and the development of cancer results from the turning on of these cells.

Before proceeding let us review a few issues. It should be noted that we are simplifying the analysis to intensify several points and let the reader focus on the literature to assist in resolving some of the lost complexities. Now:

1. Stem cells have certain characteristic and the only one we focus on here is that for the most part they are the only cells of a class which have the ability to reproduce. In a stable environment, the stem cells reproduce at a rate equal to the loss of mature functional cells. Thus in the skin, the basal stem cells reproduce at a rate equivalent to the death and loss of the keratinocytes, no more or less. Let there be an injury then they produce more by being activated by some ligand on some receptor on the stem cell. Cells reproduce until equilibrium is reached.

2. Mature cells, derivative from stem cells, do not reproduce. They just do what they were intended to do, no more or less.

As Wang and Shen state in a recent article (2011):

The cancer stem cell (CSC) model proposes that cells within a tumor are organized in a hierarchical lineage relationship and display different tumorigenic potential, suggesting that effective therapeutics should target rare CSCs that sustain tumor malignancy…CSCs are instead defined in practical terms through the use of several functional assays. The most frequently used methodology involves xenotransplantation of flow sorted populations of primary cancer cells into immunodeficient mice. In this assay, CSCs are defined as a subpopulation of cells within a primary tumor that can initiate tumor formation in mice following transplantation, unlike the remaining tumor cells

This is a definition limited to the assay produced. It is not a broad based definition.

Wang and Shen then discuss the types of prostate cells:

In human and mouse, the normal prostate gland epithelium contains three primary differentiated cell types.

1.     Luminal cells are columnar epithelial cells that express secretory proteins as well as markers such as cytokeratin 8 (CK8), CK18, Nkx3.1, prostate-specific antigen and high levels of androgen receptor (AR).

2.     Basal cells are localized beneath the luminal layer and express markers including CK5, CK14 and p63, but express low levels of AR.

3.     A rare third type of cells termed neuroendocrine cells express endocrine markers such as synaptophysin and chromogranin A, but do not express AR.

Then they allege:

Prostatic intraepithelial neoplasia (PIN) is often considered a precursor of prostate cancer, and is characterized histologically by luminal epithelial hyperplasia and a progressive loss of basal cells …

Here we have previously expressed concern regarding counter-examples. Namely it is known that there are patients where a diffuse HGPIN may be present upon a high density sampling and then after a second high grade sampling the HGPIN is totally gone. The question is why? If as many agree HGPIN is the precursor of PCa and if moreover HGPIN is already a representation of a CSC mutation, then what has reversed the mutation. Perhaps it was the fortuitous removal on the CSC in the initial sampling? We have argued that such may be inductively deduced from examining the number of times this occurred related to the statistical chance of such happening.

In a recent paper, Qin et al state[6]:

Prostate cancer (PCa) is heterogeneous and contains both differentiated and undifferentiated tumor cells, but the relative functional contribution of these two cell populations remains unclear. Here we report distinct molecular, cellular, and tumor-propagating properties of PCa cells that express high (PSA+) and low (PSA−/lo) levels of the differentiation marker PSA. PSA−/lo PCa cells are quiescent and refractory to stresses including androgen deprivation, exhibit high clonogenic potential, and possess long-term tumor-propagating capacity.

They preferentially express stem cell genes and can undergo asymmetric cell division to generate PSA+ cells.

Importantly, PSA−/lo PCa cells can initiate robust tumor development and resist androgen ablation in castrated hosts, and they harbor highly tumorigenic castration-resistant PCa cells that can be prospectively enriched using ALDH+CD44+α2β1+ phenotype.

In contrast, PSA+ PCa cells possess more limited tumor-propagating capacity, undergo symmetric division, and are sensitive to castration. Altogether, our study suggests that PSA−/lo cells may represent a critical source of castration-resistant PCa cells.


1.     PSA−/lo PCa cells are quiescent and refractory to anti-androgen and chemotherapy
2.     These cells express stem cell genes and can undergo asymmetric cell division
3.     They also possess long-term tumor-propagating capacity in intact male mice
4.     PSA−/lo PCa cells are highly tumorigenic and resist androgen ablation in vivo

We depict the details from the paper and show it below:

As Merville states in commenting on the work of Qin et al[7]:

In cell lines and mouse model experiments, the low-PSA cells resisted chemotherapy and thrived under hormone deprivation, the two main prostate cancer drug treatments, the researchers found.

Low-PSA cells were found to be both self-renewing and capable of differentiating into other prostate cancer cell types upon division, a hallmark of stem cells called asymmetric cell division. "Asymmetric cell division is the gold standard feature of normal stem cells," Tang said. "Using time-lapse fluorescent microscopy, we were able to show asymmetric cell division by filming a low-PSA cell dividing into one high-PSA cell and one low-PSA cell."

When the team implanted the two cell types in hormonally intact male mice, the rapidly reproducing PSA-positive cells caused faster growth and larger tumors in the first generation. However, after that the low-PSA cells generated larger, faster-growing tumors and tumor incidence in the high-PSA cells dropped.

In fact, the low-PSA prostate cancer cells possess indefinite tumor-propagating capacity. In contrast, when implanted in the castrated mice, the low-PSA prostate cancer cells developed much larger tumors than the corresponding high-PSA cells. In another experiment, mice with tumors generated by either cell type were then castrated and treated with hormonal therapy.

Low-PSA tumors grew better in these doubly androgen-deprived mice than the high-PSA tumors. "These findings closely resemble progression observed in patients after androgen-deprivation treatment and reflect reduced PSA-producing cells in patient tumors after androgen depletion," Tang said.

As Jeet et al state regarding their view of the prostate related stem cell:

Stem cells are unspecialized cells that can self-renew and differentiate to yield a diverse range of specialized cell types of a tissue or organ. The mouse prostate comprises dorsal, lateral, ventral, and anterior lobes, each containing three regions of proliferating cellsdistal, intermediate, and proximal. It has been suggested that the prostatic stem cells reside in the proximal region of the mouse prostate.

These findings, together with tissue recombination approaches (that allow the study of mesenchymal-epithelial interactions in developing tissues), led to the elegant work that developed a new prostate regeneration system by combining CD117 (a prostate stem cell marker predominantly expressed in the proximal region) positive fractions from C57BL/6 mouse donors with rat embryonic urogenital sinus mesenchymal stromal cells. These cells were then placed under the renal capsule of athymic nu/nu mouse hosts to generate functional, secretion-producing prostates. This is the first model to demonstrate the ability of mesenchyme to trigger prostate genesis thus opening up possibilities for developing insights into the earliest changes that evolve into cancer.

Jeet et al argue that their worked demonstrates the ability of these identified stem cells to have a form of prostate related pluripotency. They like many others have been using cell markers as a means of tracking the stem cell. One may then ask what is the cell receptors and activating ligands which result in the stem cell ability to perform its regenerative functions.

As Zhang stated:

Importantly, Staege and Max also noted that tumor stem cells in EFT have been identified. These tumor stem cells expressed some markers of embryonic stem cells. There are cell populations with the phenotype of embryonic stem cells in the adult body. It remains unclear as to whether such cell populations are permissive for EWSR1-FLI1 induced transformation and whether EFT is derived from these cell populations.

Zhang has extended this identification somewhat but the issue of good markers remains.

Yet as Gupta et al state:

Some of the controversy surrounding the CSC model seems to arise from confusion regarding the definition of CSCs, leading to two key objections against the use of this term.

 The first objection derives from the fact that, unlike the case for normal stem cells, which are usually oligo or multipotent, it is currently unclear whether CSCs can give rise to multiple differentiated cell types….

A second key objection to the CSC model is that it is currently unclear whether the normal cellular precursors of CSCs are, in fact, bona fide stem cells. It is clear, however, that the traits used to define CSCs do not rely on knowledge of their cellular origins within normal tissues. Accordingly, the CSC model must stand or fall on the basis of experimental characterizations of cancer cell populations

The Gupta et al observations are quite important. Namely, is a stem cell born or made. Namely is there an unbroken lineage from stem cell to stem cell? Also his first observation is the pluripotency issue, namely, are stem cells able to generate a broad number of cells or are stem cells cell-specific? The current nature of the Gupta et al observations do raise issues as to how well we understand the stem cell model.

As Tang et al conclude:

The hypothetical model of hierarchical organization of PCa cells has several important implications. Above all, it can help explain how the tremendous heterogeneity associated with the PCa can be generated. The rare PCa SC that persist in a tumor will continue to generate a repertoire of progenitor cells that in turn will develop into a spectrum of cells at different stages of differentiation , thus engendering the heterogeneous phenotype of the tumor. The model posits that the tumorigenic stem/progenitor cells are mostly undifferentiated cells as supported by the observations that most CD44 and CD133 cells are AR. The model also implies that most differentiated, luminal-like cells, which constitute the bulk of the tumor, might be much less or even non-tumorigenic (Figure 6A). In support, prospectively purified CD57 cells are non-clonogenic and non-invasive [44] and prospectively purified PSAþ cells are less tumorigenic than the isogenic PSA_ cells.

They also note the positive and negative PSA in the prior paper by Tang.

There is a great deal of concern as regards to where the stem cells come from. Namely the issue of the cells of origin. Previously we had reviewed the Goldstein model, where they had indicate a basal stem source as compared to a luminal cell source.

Wang and Shen state:

The identification of normal cells that can serve as a cell of origin for prostate cancer is highly relevant for understanding the applicability of a CSC model, and is currently under intense investigation. The cell of origin may also have clinical significance, as in the case of breast cancer, distinct tumor subtypes have been proposed to originate through transformation of different progenitors within the mammary epithelial lineage hierarchy. Thus, it is conceivable that there may be distinct cells of origin for other epithelial cancers, and different cells of origin may give rise to clinically relevant subtypes that differ in their prognosis and treatment outcome.

They consider several sources. For basal cells they state:

Although prostate tumors display a strongly luminal phenotype, this does not exclude the possibility that basal cells could be a cell of origin for prostate cancer. In particular, it is possible that transformed basal cells could differentiate to generate large numbers of luminal cancer cells. For example, prostate-specific conditional deletion of Pten by a probasin-Cre driver allele has been shown to result in a basal cell expansion accompanied by increased number of intermediate cells, suggesting a basal cell of origin … An important recent study from the Witte laboratory has used similar approaches with primary human prostate tissues to show that basal cells are a cell of origin for human prostate cancer

The Witte lab results are those of Goldstein et al which we have discussed at length (See Appendix A).

In contrast we have luminal cell origin as stated as follows:

Other studies have provided evidence that luminal cells can serve as cells of origin for prostate cancer. For example, pathological analysis of high-grade PIN samples, which still retain basal cells, suggest that molecular events associated with human prostate cancer initiation such as upregulation of c-MYC and shortening of telomere length occur exclusively in luminal cells but not their basal neighbors …

In Moscatelli and Wilson, the authors state:

There is nothing inherently contradictory in the results described by Wang et al. and Goldstein et al., because it is possible that both basal and luminal stem/progenitor cells may independently serve as cells of origin for prostate cancer.

Indeed, it is also possible that oncogenic stimuli may differ in their effectiveness in transforming distinct cell populations. The tumors that arise from different target cells may also vary in their biological behavior and genetic profiles.

There are also indications that normal prostate stem cells may reside in both the basal and the luminal compartments. Thus, if stem cells are preferentially targeted during malignant transformation, both compartments may contain cells of origin for prostate cancer.

Most of the scientific evidence indicates that prostate stem cells reside in the basal layer and give rise to the secretory luminal cells via transit-amplifying cells, which are intermediate in phenotype between stem cells and terminally differentiated cells.

There is definitive evidence that

(i) secretory cells of the adult murine prostate derive from cells that express p63, a transcription factor that is expressed by all basal cells in the prostate , and

(ii) p63- expressing basal cells are required for prostate development. In addition, prostate basal cells (human and murine) have greater proliferative activity in vitro and in vivo than luminal cells.

The molecular signature of prostate stem cells also identifies a basal-like phenotype, as they express cytokeratins 5/14, p63, and integrin á6 (11). There is also evidence, however, that the luminal compartment may contain stem/progenitor cells and that these give rise to basal cells.

Experiments involving labeling cells with the synthetic nucleoside bromo-deoxy-uridine to detect those that are proliferating indicate that slow-cycling stem cells are concentrated in the proximal region of prostatic ducts adjacent to the urethra and that both basal and luminal compartments contain slow-cycling cells. Cells from this region have substantial growth potential in vivo and in vitro and can be serially passaged in vivo at least four times. It is not known whether CARNs are concentrated in the proximal region, but if so, CARNs may comprise some of the slow-cycling proximal luminal cell population.

These results provide a possible means to address the CSC signature issue. However, it is not clear that the result is definitive nor of immediate clinical use.

Stem cells are known in hematopoietic cell generation. They are isolated, separate and their ability to develop the full plethora of blood cells is well known. The stem cell concept applied to say prostate cells or skin cells is of more recent structure and is in many ways still open for debate. Taking that construct one step further and considering a cancer stem cell is possible even more of a conjecture. We can accept the concept of a cancer stem cell in the many blood cancers. We know that CML may very well have a translocation, as is found in other leukemias. Yet the establishment of the same for say prostate and melanoma malignancies is I believe still a work in progress.

For example as Jeet et al state:

Different stages of prostate cancer progression: (a) prostatic intraepithelial neoplasia, a premalignant lesion considered to be a precursor to invasive carcinoma; (b) primary localized adenocarcinoma, dependent on androgen stimulus and can be treated by androgen ablation; (c) androgen-independent prostate cancer, tumor then becomes androgen independent and metastasizes to other organs (e.g., lung, bone, and lymph node)

The linear progression we have disputed in prior writings based upon clinical observations. The reason is that we have observed the remission of diffuse HGPIN in patients at first biopsy and then the absence in subsequent. Not just reduction of HGPIN, but total elimination. Our hypothesis is that there has been the presence of a stem cell and its removal during the first extensive core biopsy, usually 16 or more cores, not classic sextant biopsy.

Stem cells are a powerful paradigm which may very well align with the clonal model. For if it is the stem cell which has suffered the genetic change then if this cell has the controlling powers attributed to it, then the stem cell model will also tell us a great deal regarding treatment, and our inability to do so.

For example, a stem cell will itself generate other stem cells as well as non-stem cells.

There are many questions still posed regarding the cancer stem cell:

1. What are the pathway dynamics and are they the same in the non-stem like cells?

2. What is the driver for the kinetics of a CSC? Namely do we have a dramatically different set of kinetics?

3. What is the mechanism for the progression of subsequent mutations in a CSC?

4. How do we identify the CSC in a sample biopsy? Are there specific cell markers and are they consistent or do they change?

5. What are the driving ligands which activate a CSC?

6. Do stem cells have true pluripotency or are they cell specific?

7. What are the stem cell surface ligands and receptors which promote mitosis and how are they transmitted across a group of cells?

8. What causes a stem cell, specifically a CSC, to evolve and how does that occur?

We can continue with a great number of these types of questions. However if one hopes to be able to model cancer pathway dynamics one must first address the issue of the CSC, for if the CSC has the definitive characteristics that we have discussed then it and it alone is what should be focused upon. Furthermore the examination of cells for pathway markers may very well have to be done only on the CSC, which then argues that we need sophisticated techniques to identify them and extract them as well.

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