At the risk of offending you further, you just made my point for me, perfectly.
You clearly care deeply about the cause of brain cancer. Not because you objectively evaluated all of the issues affecting mankind and decided that brain cancer is the most serious one where your attention could produce the most benefits, but because it directly affected you. That's entirely my point.
Had you never contracted brain cancer, you would most likely continue to afford it the same consideration as you do many other equally serious causes, like Lou Gehrig's disease, or ALS, or Boko Haram kidnapping young girls and forcing them into marriage. But none of those things affect you.
I'm not saying it's bad, or even irrational. Of course you care more about things that affect you directly than the things that don't. I'm just saying it doesn't make you a hero.