Stem cells are noted by two primary characteristics: the ability to renew themselves by cell division, and to differentiate into a wide range of specialized cells. They are under tight biological control, with a balance between self-renewal and differentiation. Cancer stem cells have similar processes, but these processes are abnormal and unregulated. Reya

Where do Cancer Stem Cells Come From?

Tumors consist of a heterogeneous group of cells as a result of accumulated mutations. Controversy exists within the scientific community if cancer stem cells can even be isolated and characterized. Several hypotheses have been brought forward to account for the appearance of cancer stem cells:

  • Cancer stem cells could arise from normal stem cells. Since stem cells are long-lived, there is ample opportunity for multiple mutations to arise, eventually to lead to cancerous cells.
  • Cancer stem cells could arise from so-called progenitor cells. Progenitor cells are further along in development than stem cells, and can only differentiate into a specific type of cell. In this sense, progenitor cells can be thought of as intermediate between stem cells and the final differentiated cells.
  • Finally, cancer stem cells could result from mature, differentiated cancer cells that revert back to stem cells, but maintain their cancerous nature.

What is the Significance of Cancer Stem Cells?

Proponents of the cancer stem cell hypothesis state that tumors consist of two types of malignant cells. Most of the tumor consists of rapidly growing cells that are hypersensitive to certain biochemical signals that lead to proliferation. A much small number of cancer stem cells are also present that are more quiescent, long-lived and not as sensitive to these signals. Cancer treatments usually focus on attacking the rapidly growing cells. The tumor shrinks, and the patient appears to be cured. However, the cancer stem cells manage to survive the treatment, multiply, and the cancer recurs. This newly recurred cancer is now resistant to all treatments, and the cancer spreads.