Twentyseven year old Adam (Joseph Gordon-Levitt) doesn't drink or do drugs. He waits religiously at DON'T WALK signs before crossing even when the street is deserted and he's never driven a car out of fear of injury or worse. So when Adam is diagnosed with cancer of the spine and given 50/50 odds of surviving it's as if someone repealed the law of gravity.
The task of helping him over the hurdles of chemotherapy and radiation falls on his Rabelaisian best friend, Kyle (Seth Rogen) who will stoop to anything to take advantage of the opposite sex even exploiting Adam's cancer as a sympathy technique to pick up dates. Think Oscar and Felix of the Odd Couple when trying to imagine a relationship like Adam and Kyle's. Kyle gets some stability in his otherwise chaotic life and Adam gets to let loose vicariously through Kyle.
Adam's fickle girlfriend, Rachael (Bryce Dallas Howard) is a shallow and self-indulgent:artist the kind of girl Adam likes to date so he can remain comfortably detached.
His relationship with his doting mother Diane (Angelica Huston) is strained.
Katherine (Anna Kendrick) is a novice therapist helping Adam cope with his terminal illness and given what a tight rein he keeps on his emotions it's not easy. Add to that her lack of experience and his need to control situations and sometimes it seems as if he's the therapist and she's the patient.
Will Reiser's script based on his own experience with cancer has humor and pathos making 50/50 an entertaining take on an otherwise grim subject.