Researchers discover evidence of cancer stem cells

Cancer stem cells are the cause of tumors

08/02/2012

Often, cancer returns after a supposedly successful surgery, chemotherapy or radiotherapy. As a cause researchers suspected since the late 1990s so-called cancer stem cells that are not destroyed in chemo- and radiation therapies and subsequently lead to the formation of new tumors. The theory has been controversial so far. But now three different studies published yesterday in the journals "Nature" and "Science" provide new evidence for the existence of corresponding cancer stem cells.

In a review of the journal Science, the results of the three recent studies on cancer stem cells are summarized as a relatively clear indication that "in certain brain, skin and intestinal tumors cancer stem cells are the source of tumor growth." This contradicts the previous assumption of the monoclonal cancer formation theory, according to which all cancer cells are the same and each one - if it has the ability to divide cells - can be the starting point of new tumors. However, the stem cell model postulated by Canadian researchers in 1997 assumes that there is a hierarchy of cancer cells. Accordingly, the normal cancer cells are produced from the cancer stem cells, the proliferation of which then causes tumor growth.

Hierarchical structure of cancer cells?
The model of cancer stem cells states that tumor growth is structured hierarchically, with only a small subset of the cells forming the basis of cancer, the statement in the journal "Science". The model was developed by Canadian geneticists in the late 1990s, after they observed in experiments with mice that in leukemia only "a small subset of the cancerous blood cells can propagate the disease". This new approach seemed particularly promising, as the failure of chemo and radiotherapy, which only attacks the common cancer cells, could be explained in this way. The cancer stem cells thus survive the treatment and then ensure a renewed tumor growth. Yet, finding the cancer stem cells that fuel the growth of tumors in other tissues has been extremely difficult.

Cell labeling techniques detect cell growth in tumors
The definitive evidence for the existence of cancer stem cells can not be provided by the three recent studies, but the evidence is clear. For example, Cédric Blanpain of the Université Libre de Bruxelles and his team in the journal Nature report that in mice in benign papilloma tumors, a precursor to skin cancer, "most of the tumor growth is triggered by a few cells, which in some respects stem cells of healthy skin. "For identification purposes, the scientists independently used genetic cell labeling techniques in all three studies to monitor the proliferation (cell proliferation) of certain cells in growing tumors. According to Cédric Blanpain, this method provides scientists with insights into "the real life of a tumor." Comparable cell differences as in papilloma tumors were reported by the researchers in invasive spinal cell carcinomas, but the results were less clear.

Stem cell activity in precursors of colorectal cancer
The Dutch scientists led by Hans Clevers from the Hubrecht Institute in Utrecht also devoted themselves to the cancer stem cell hypothesis in their study. Using "mouse models, we provide direct, functional evidence for the presence of stem cell activity in primary intestinal adenomas, a precursor to colorectal cancer," write Clevers and colleagues in the journal "Science." However, the researchers did not conduct studies on intestinal tumors, so it remains unclear whether the stem cell properties also play a role in carcinomas. The "stem cell activities" were detected in five to ten percent of the cells in the adenomas, the Dutch researchers report.

Cancer stem cells detected in brain tumors
The third current study on the hypothesis of cancer stem cells published the evolutionary biologist Luis Parada from the University of Texas Southwestern Medical Center (Dallas, USA) and his team also in the journal "Nature". They investigated the cell characteristics of gliomas (brain tumors) in mice. "Glioblastomas are the most common malignant brain tumors," report Parada and colleagues. The average survival time, according to the researchers is only about a year. The prognosis was particularly poor because of the resistance to therapy and the frequent re-growth after surgical removal. In the mouse model, the researchers therefore looked into the question of why the brain tumors occur so often after supposedly successful therapy. According to the scientists, after chemotherapy with temozolomide, the animals survived a "relatively quiet part of the endogenous glioma cells, with properties similar to those of cancer stem cells." These cells could be responsible for ensuring long-term tumor growth through the production of highly proliferative cells , so the conjecture of Luis Prada and colleagues. Because after termination of the therapy, the cells could be stimulated to a renewed tumor growth.

Understanding of cancer stem cells crucial for cancer therapy
All three research groups emphasize in their recent publications that understanding the function of putative cancer stem cells is the key to more effective therapy. Which cancers develop from stem cells should therefore be investigated in upcoming studies. However, according to Sean Morrison of the University of Texas Southwestern Medical Center, "this is not an easy task as tumor growth differs even among patients with the same type of cancer." However, recent studies have increased the incentive for other scientists to To research the cancer stem cell hypothesis, Luis Prada explained. Here, the so-called "cell tracing methods are the right approach to test the cancer stem cell model," says Morrison. (Fp)

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Picture credits: Sigrid Rossmann