Cancer Stem Cells
• A tumor is made up of a diverse population of cells. This is why you might often see the words ‘heterogeneous population of cells’ in the context of a tumor. It just means that there are lots of different types of cells within one tumor.
• Cancer stem cells (CSCs) are a subset of cells found within a tumor that have two main characteristics: they are self-renewing (just like normal stem cells) and they can differentiate to form more cancer cells. CSCs are implicated in relapse and metastasis, because they are notoriously resistant to chemotherapy and radiation when compared to non-stem cancer cells.
• In cancer research, tumor cells are sometimes injected into immune-compromised experimental animals to establish a tumor. Disease progression can be followed and drugs can be tested on these animals. Usually it takes about 20,000 to 1,000,000 non-stem tumor cells to do this. However, CSCs require far less cells to establish a tumor, usually around 200, and there are even reports where a single cell could be used to establish a whole tumor (sorry, article is behind a paywall).
• The fact that CSCs appear to be the culprits in tumor initiation and relapse would indicate that finding a therapy to target the CSCs specifically might be the most effective way to cure cancer – after all, if you can somehow wipe out the root
cause cells, surely the rest of the disease would also follow? Unfortunately no, the story is more complicated than that.
• Recent work has shown that non-stem tumor cells are capable of undergoing a de-differentiation program to repopulate the tumor (Open Access – yay!). So if one were to eliminate CSCs within a tumor using a targeted therapy, some of the surviving non-stem tumor cells will generate new CSCs through spontaneous de-differentiation. What this means is that the ideal therapy should be a combination therapy, made up of traditional drugs that target non-stem tumor cells and also drugs that can specifically target CSCs.
To learn more about CSCs, watch this talk from Robert Weinberg about CSCs: