Question

My grandmother has advanced cancer, and has her 90th birthday coming up in two months. The doctors say she's very unlikely to live so long, but she's very determined.

Is it true that people dying of cancer can temporarily postpone dying for something like this?
 

Answer

There are lots of stories and reports of people like your grandmother being able to survive until after a special event - a birthday, a family wedding, or the birth of a grandchild or great-grandchild. However, it seems likely that these are just the "positive" reports - the "negative" ones don't get published or passed on.
 

Some scientists in Ohio have studied this supposition (see the publication listed below). They analyzed death certificates from a 1,250,000 people, which included over 300,000 dying with cancer. They counted the number of cancer deaths in the one week before and the one week after Christmas, Thanksgiving and the person's birthday. There were no differences between the before and after numbers for any of these special events, except for an increase in cancer deaths for women in the week before their birthday, and for African-American men in the week before Thanksgiving. It's likely that these differences occurred by chance, however.
 

Sorry to bring apparently bad news. It seems unlikely that your grandmother's determination will alter the course of events, based on this study, but you never know - doctors are notoriously wrong in predicting how long people will live.
 

Footnotes
1. Hookey LC, Depew WT, Vanner SJ. A prospective randomized trial comparing low-dose sodium phosphate plus stimulant laxatives with large volume polyethylene glycol solution for colon cleansing. American Journal of Gastroenterology 2004;99:2217-2222