Uh, well, everyone else seems to have it covered. I'd ask to see some of what you've actually written but I realise how positively criminal that sounds (I never did before joining here, so there goes another thin layer of my innocence).
Personally I'm against the idea of changing between first and third person. There doesn't seem to be any subtle, consistent way to do it. Or any good way, for that matter, as far as I know (which isn't very far, admittedly). You might try introducing a very personal style of third person. I'm not a fan of actually writing what a character is thinking -- you know, 'show don't tell' and all that -- but sometimes this can be a good way to introduce a tiny bit of first-person and if you've violated your own word limit maybe a bit of telling and not showing will help.
Additionally, miss lambeychops, did you do a lot of research on cancer? I was of the idea that once treatment for it began it was kinda obvious through a few symptoms that the person in question, well... had cancer.
