Stem cells hold great hope for advances in medicine, but they also have a dark side: their potential to turn malignant, according to a recent article by Michael Clarke and Michael Becker for Scientific American. Most of us think that any cancer cell remaining in the body has the potential to cause a relapse of the disease. Not true, according to Clarke and Becker, who write that in a few cancers “it is now clear that only a tiny percentage of tumor cells have the power to produce new cancerous tissue.” The best way to treat these cancers is to target these specific cells, called cancer stem cells. Most surprisingly, cancer stem cells are believed to have once been normal stem cells that have somehow undergone a change.
Our bodies are continually reinventing themselves; cells die and are replaced by a highly-regulated and compartmentalized system within the body. The most promising stem cells are those that are created by this system. Clarke and Becker cite the hematopoietic stem cell (HSC), originating in bone marrow, as an example: “The HSC pool represents less than 0.01 percent of bone marrow cells in adults, yet each of these rare cells gives rise to a larger, intermediately differentiated population of progenitor cells. Those in turn divide and differentiate further through several stages into mature cells responsible for specific tasks, ranging from defending against infection to carrying oxygen to tissues.” When the HSC cells reach maturity they no longer are able to differentiate and their die, so to speak, is cast.
If the HSC cells can be harvested before they mature, perhaps virtually any type of tissue can be grown. This holds tremendous promise for a great many diseases. Furthermore, study of these stem cells may reveal how cancer spreads.
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