Does Aspartame Cause Cancer?

I was trying to think of how I (all of a sudden) had brain cancer.  The doctors said they didn't know how or when I got it (it was determined July 29, 2011).  When I looked it up online, the only reason I found was the use of aspartame because most answers everywhere also said they didn't know the cause.

I read everything about cancer+aspartame, mostly because I used aspartame for at least 30 years as sweeteners in my coffee so that I would have it with fewer calories than sugar.  When I was younger and actually drank pop, I also had diet pop only, and over the recent years where I became addicted to 'breath-freshening' Excel gum, found it was made with aspartame.  By the way, I went looking for non-aspartame gum recently and there was none - all gum was made with aspartame.

If you search online for details on aspartame, most of what you find (especially from aspartame creators) will say that cancer 'may' have been found in researching rats - but not people.  If you find other websites, you'll find that they think it's the cause of brain cancer.

Reality is that I've been told by the doctors that I will live for 15 months.  15 months from when, I don't know.  Maybe it means after chemo and radiation have finished?  I have the malignant glioma, Level IV type in my temporal lobe.  In the current time, I figured I'd quit aspartame so, hopefully, it wouldn't make me any more cancerous.

Since I couldn't like my coffee black, I switched from aspartame to Xylitol, which, as I've read, is supposed to be healthy, not like aspartame.  I like the idea because it's fewer calories than sugar (which I've always avoided because I didn't want to gain weight).  The good thing about xylitol seems to be that you can also order gum made with it.  I am going to do this to see if it provides a gum I'll be happy enough to chew on (meaning not overly rough chewing and flavours that last a bit long).  It would be good if something worked for me at preventing the growth I think they'll be finding a month after my current radiation has finished.