I’m sorry to hear about your friend’s cancer. My favorite writing about how “guestimated” survival timelines can be bullshit is by the prominant paleontologist Stephan Jay Gould, who lived about 20 years after his diagnosis said he’d live only another 8 months:

http://www.cancerguide.org/median_not_msg.html

It’s a little bit on the brainy side about why statistics can lie and bring people down, but different things appeal to differ folks and I’m more of a take-comfort-in-the-analysis-of-numbers guy myself than spiritual/religious.