Stem Cells and Cancer Article
I’ve written several times in the blog about research showing that stem cells are likely the source of many cancers; something confuses the mechanism by which they regulate their production, and they overproduce new cells, creating a tumor. Now Scientific American
has published a fairly lengthy article on the subject (6 pages on the web). It is not a statement of any new research findings, but an overview and synthesis of what is already known. Some of the key points:“The HSC [hematopoietic stem cells] 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.” Once the cells have differentiated to perform specific tasks, they can’t revert to performing some other function. The progenitor cells produced by the stem cells can divide multiple times but not limitlessly, as stem cells can.
“Because the rare stem cells are the only long-lived cells in the organs where most cancers develop, they represent a much smaller potential reservoir for cumulative genetic damage that could eventually lead to cancer. Unfortunately, because stem cells are so long-lived, they also become the most likely repository for such damage.” In other words, because stem cells are “immortal,” they suffer a greater likelihood of mutating than other cells which die quickly do; the regular cells simply aren’t exposed to the carcinogen for the length of time the stem cells are.
There are two models for the mechanism by which stem cells cause cancer; one is that there is a mutation in the stem cells themselves, and one is that the mutation occurs in the progenitor cells. This second theory would require progenitor cells to gain the ability to self-proliferate indefinitely, which has been shown to happen in at least one form of cancer.
Crucial developments in the research include the commercial availability of the flow cytometer in the 1970’s, which allows research to separate different populations of cells within one sample, and the work in the 1990’s which showed that some cells had self-renewal properties.
The niche signaling properties related to stem cells—the messages they receive from the cells in the area of the body surrounding them—is a key to stem cell development and growth. It is possible that the niche cells would have the potential to send non-proliferation messages to cancer cells, to keep a tumor from growing; the environment of the stem cell is crucial.
Other parts of the article detail some of the specific instances in which stem cells have been shown to be at the root of the cancer, and some possible methods for treating cancer based on what is known about stem cell behavior. If this is an area you are interested in, please read the entire article yourself as I can’t possibly do it justice.
There was one other point that I wanted to comment on, which is that many of the discoveries of cancer stem cells have come from cancer researchers rather than stem cell researchers. This again shows how closely related the various biological fields are, and how research in one area can have an impact in another. This is one of the ways in which the limitations on embryonic stem cell research, sometimes so tight that graduate students in one lab can’t converse with students in another, stifles overall scientific knowledge.