This topic came up a little while ago, and I posted a response based on some searches of the medical literature. Basically, you shouldn't believe everything NBC News says about medicine -- journalists by definition don't know anything and just pretend they do. It isn't uncommon for these "cancer clusters" to pop up every so often, but usually it's just anecdotal. Aircrew members who think they might get cancer usually get overly upset when a colleague gets cancer and attribute it to flying, even though statistically that may not be borne out. That being said, there have been a number of scientifically controlled studies done on this issue, and the results are unclear. Some studies do show higher risk for cancer for flight crew, some don't. Some found higher risk, but these results disappeared when they controlled for leisure time activities. Translation: pilots are at higher risk for cancer not because they fly, but because they are statistically more likely to enjoy sunbathing than the general population. So you need to look very closely at how the study was done and what variables they controlled for when the media flashes a "5 times higher risk" figure at you. Otherwise it's just sowing paranoia.