Case Study: Leukemia and the discovery of cancer stem cells (CSCs)
In the history of cancer, leukemias have often been a window into larger truths about cancer in general. Chemotherapy, for instance, was shown to be effective in leukemia well before physicians had the idea to try it on solid tumors. The scientific and medical clarity offered by leukemia is due in large part to the ability of researchers and physicians to easily take blood samples and identify the various cellular components of the blood cancers.
In leukemia, the normal bodily functions are threatened because the bone marrow or blood becomes glutted with immature blood cells (in acute leukemias) or more mature blood cells (in chronic leukemias). In the 1990s, leukemia researchers isolated a different subpopulation of leukemia cells: these cells were not by themselves clogging bone marrow or blood vessels, but they had one important feature. Unlike the more numerous and problematic leukemia cells, a relatively few of these rarer cells could transfer a leukemia from a sick mouse into a previously healthy one. The implication was that these cells were the critical stem cells that actually caused the leukemia and gave rise to all the other immature or mature blood cells that clinicians saw in the samples under their microscopes. Since that time, researchers have found similar CSCs in most kinds of solid tumors such a breast cancer, bladder cancer, colon cancer and liver cancer.