Many of us who have watched a loved one suffer through cancer treatments sort of suspected this might be true: some solid tumor cells that avoid being killed by radiation or chemo actually become tougher and better able to survive the next round of treatment.
Unfortunately, it's a lot like what Friedrich Nietzsche said: whatever doesn't kill me makes me stronger.
A Duke team led by Mark Dewhirst in radiation oncology has figured out how and why this happens: The solid tumor cells' innate ability to signal surrounding tissues to give them more oxygen gets turned up a notch by the treatment assault. Next time around, they're that much better able to resist.
Dewhirst and colleagues are now working on ways to turn off this gimme-oxygen signal in conjunction with chemo and radiation to really root the @#$%@s out. They've also made a movie showing the constant flux of oxygen in tumors, rising and falling like the tides. It's something that's only recently been identified.