Just jumping into the throng here because I can deeply relate to your problem, and in a slightly different manner is something I struggled with when applying to graduate school last year.
Some background: I am a doctoral student at a very good program (different field, but still). I had medical (not cancer) issues that bogged past as well. I actually dropped out of college with failed classes and resumed with a different major four years later.
As other answers said - mention it in the personal statement, make it matter-of-fact. I woven it in a single paragraph that was structured somewhat like this:
I wanted to to X. Got sick. Tried my best but my medical issues got the best of me for a time. Worked hard to get better. Tried again because the time spent away enabled me to reassess priorities and my academic path shined through. Now I am better and very committed.
In my statement of purpose I decided not to mention any of this. So my advice: Write about it. Only in the personal statement. You don't even have to mention the specific issue (i.e., cancer) - especially if you are better now. It is nobody's beeswax at this stage. When you do write about it (did I mention that you should write about it? ;)), frame it very carefully. DO: The single most important thing you can do is explain, briefly, how your experience made you realize what is important to you (i.e., graduate work). DON'T make this the only core point about who you are, and do not over sell how you overcame adversity - like everything in your statement (personal and research) - show is better than tell. It should be evident, not self-boasting.
Good luck!