Cancer as Evolution, part 3
Kevin points out that perhaps I am giving chemotherapy short shrift and not looking at the bigger picture. I would counter that you can't really make the latency analogy with human life because we are all born terminal. "Mean survival time" is a squirrely measure at best because how do you know if someone died (a) because of the cancer, (b) because of the chemo, or (c) because of some other factor (in which the cancer or chemo or both) could be confounding? If you buy the somatic evolution (SE) argument then there are all sorts of consequences which contraindicate chemo in most cases. Just for instance, there is good experimental evidence that SE is punctuated (as in "punctuated equilibrium"). If you introduce stress into the population at the wrong time, you tip the system into a regime that is bad for the human (good for the cancer cells). A more auspicious time to apply chemo (according to SE) might be before symptoms occur. But doctors and patients are perhaps more likely to be aggressive with chemo at precisely the wrong time. Another consequence of SE is the "cleverness" of the disease in terms of routing around the brute-force obstacles we throw at it. Chemo is just the sort of unspecific and mild selective pressure that evolution is really good at adapting to. So instead of mere drug resistance, chemo is really creating a new system which thrives in the presence of chemo; if you don't kill every potentially bad cell, you could be worse off than when you started. But comprehensiveness is hard to achieve because after all, the cancer cells are yours to begin with and there is strong selective pressure for them to learn to evade detection, not play nice in the cell-signaling game, etc. The only way we know how to tell whether a cell is cancerous or not is by observing its behavior in the presence of other cells in the body of the organism in question. I would like to re-iterate, I am not bashing chemo per se, just that it's in a class of potential solutions which are based on a theory of what cancer is that is fundamentally incompatible with the evidence. Furthermore, one theory which is compatible with the evidence -- somatic evolution -- suggests that if you start with a chemo approach, you will always be patching a leaky boat with material that is corrosive to the boat itself. A final piece of circumstantial evidence comes from an experiment you can do yourself. Find as many practicing oncologists as you like, get them to speak to you off the record, and ask them the following question: "If you or a family member was diagnosed with a common form of solid cancer (breast, colon, etc), would you administer chemo?" Previous such surveys suggest that less than 25% would choose chemo for themselves, but nearly all of them would for their patients (due to malpractice concerns). BTW, somatic evolution is not the end-all-be-all in cancer theory. There are other dynamics at play too. Or more precisely, evolutionary theory as currently understood by most people in life sciences is not complete enough to account for these other important dynamics. One of these that I think needs to be reconciled and explored in much greater depth is what's known as aneuploidy. Aneuploidy as it applies to cancer refers to any sort of damage done at the level of the chromosome (as opposed to the gene-level, which sits below the chromosome level). In cancerous systems, the gene-level dynamics can look extremely stochastic, while at the same time, genome-level (i.e. chromosome-level) dynamics show remarkable patterns. Why this isn't addressed in most cancer research at this time is a larger discussion about how science advances in the real world.