Jonathan Levine's 50/50 claims that it is based on a true story, and, frankly, I believe it.
It should be noted, however, that no matter how real the story on which it is based, the film's trouble is that it leaves reality completely behind. I didn't hate the movie by any means, but 50/50 is uncomplicated, easy, and rather obvious. The young man at the film's center learns everything we expected him to learn after the film's first act, and the movie lacks both surprises and wisdom.
When I say that 50/50 is unrealistic, it's because everything is just so easy. The bad girlfriend is bad from the movie's second scene and all that's left is for the main character to realize what the audience and the man's best friend already know. And the film sets up a bunch of conventions at the beginning – a job that we see only in act one, a habit of nail-biting that lasts only through the first half, a friend played by Philip Baker Hall that inexplicably disappears after act two, a habit of pot-smoking – that it loses track of completely by the film's end.
Even the medical scenes are played broadly – in a kind of whimsical parody of healthcare in the United States: some doctors are really really terribly automatons who have no capacity for feelings and all of the others care so much they fall in love with you and give you rides home when you have to wait for the bus. I am being glib. And this is a film that is interested in whimsy and charm and actually doesn't ask much of the audience, so I should be less glib about it. It is a rather harmless movie, but also, when it comes down to it, rather contentless, as well.
I do think that the poster is pretty great, though. And Seth Rogen is funny. I found him very charming.
Also, I still love Joseph Gordon-Levitt and will see everything he's in no matter what.