Have cancer researchers discovered the true enemy?

Discussion about cancer stem cells as a cause of tumors

07/10/2012

Do tumors develop their own stem cells, which lead to a constant recurrence of cancer? After three studies in August provided new evidence for the theory of cancer stem cells as the cause of recurrent cancer, experts in the field an intense debate on the potential of this since the late 1990s known approach has flared up. It may be necessary to adapt the previous cancer therapies in principle.

Often the cancer returns after supposedly successful surgery, chemo- or radiotherapy. The three independent studies by researchers from the Université Libre de Bruxelles (Belgium), the Hubrecht Institute in Utrecht (Netherlands) and the University of Texas Southwestern Medical Center (USA) suggest that so-called cancer stem cells are responsible for the onset of cancer , The treatment would therefore not only be aimed at the elimination of the cancer cells, but also the cancer stem cells. The studies were published in the specialist magazines „Nature“ and „Science“.

Cancer stem cells Source of tumor growth
The results of the three recent studies provide relatively clear indication, „that in certain brain, skin and intestinal tumors, cancer stem cells are the source of tumor growth“, reported the journal „Science“ in a review at the beginning of August. Researchers from the United States and the Benelux countries have fiercely argued that they contradict the previous assumption of a monoclonal carcinogenesis theory in which all cancer cells are equal and each cell with the ability to divide cells may be the starting point for new tumors. The cancer stem cell theory assumes that there is a hierarchy of cancer cells. The cancer stem cells are to be distinguished from the other cancer cells and essentially responsible for the re-emergence of supposedly conquered cancers.

Confirmation of the cancer stem cell hypothesis in the mouse model
The scientists around Cédric Blanpain from the Belgian Université Libre de Bruxelles came according to their article in the journal „Nature“ in the study of benign papilloma tumors, a skin cancer precursor, to the conclusion that „Most tumor growth is triggered by a few cells, which in some ways resembled the stem cells of healthy skin.“ Normal human stem cells can reproduce all sorts of other cell types, but the so-called cancer stem cells serve to grow cancer cells. The Dutch researchers led by Hans Clevers from the Hubrecht Institute in Utrecht have examined the cancer stem cell hypothesis in their study and found that in the „Mouse models provide direct, functional evidence for the presence of stem cell activity in primary intestinal adenomas, a precursor of colorectal cancer“, reports the trade magazine „Science“. Also, the non-participating, recognized cancer specialist of the University of Houston, Jeffrey M. Rosen, sees in the current studies, a confirmation of the cancer stem cell theory.

Cancer stem cells cause brain tumor reoccurrence
The clearest evidence of the existence of cancer stem cells was provided by the evolutionary biologist Luis Parada of the University of Texas Southwestern Medical Center also in the journal „Nature“ published study. Parada and colleagues had injected mice with labeled cancer cells from glioma (brain tumors). The resulting tumors in the brain of the mice were treated with the help of chemotherapy. Although the majority of the treatment was successful and the tumors could be eliminated, the cancer usually broke out again relatively soon after treatment. According to the results of the US researchers survived in the mice „relatively quiet part of the endogenous glioma cells, with properties similar to those of cancer stem cells.“ These could, according to Luis Parada „true enemy“ his. The cancer stem cells are „through the production of highly proliferative cells for ensuring long-term tumor growth“ responsible, said the US researchers. Initial unrepresentative studies in humans have provided comparable results.

Adaptation of cancer therapies required?
In all three studies to test the cancer stem cell hypothesis, scientists used genetic cell labeling techniques to track the proliferation (cell proliferation) of certain cells in the growing tumors. The cancer stem cells thus obtained survive the chemotherapy and then reproduce new cancer cells, which could continue to multiply. Successful treatment should therefore also locate and eliminate cancer stem cells. However, whether an appropriate adaptation of cancer therapies will actually be necessary will only have to be examined in further studies on humans. It also remains unclear how the cancer stem cells can be killed without harming the organism too much. However, the scientific discussion in cancer research is now moving in a new direction. (Fp)

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Picture credits: Dieter Schütz