I'm interested in the sort of choices we are going to have to make as we keep extending human lives. Amazingly, more and more people live past 40 and miss out on plagues! As we shape our environment we avoid the more tried and true aspects of natural selection, but have yet to adapt to the new pressures we're creating. For instance, people born with weak heart valves don't die as often now. We've developed a whole suite of technologies to keep them around. A lot of medical technology is like this, expending resources to reshape selection pressures.
Others have already pointed out that breast cancer tends to strike after, or at least late in, the fertile years of a woman's life. If there wasn't any medical science available, it's still unlikely that this particular gene would be pushed out of the population. It's only now that woman live long enough to witness its long term effects. So, in this case, we are selecting out a gene that wouldn't have been touched by "nature".
Hell, I no longer know my own point. Just typing aloud. I guess I'm wondering if there is an ethical difference between treating diseases that would have likely been selected out overtime and those that are only problematic because we are extending our lives through medicine? Man, I'm going to get some coffee and think...why do I read things like this?