How impressive is 50/50, a movie that could easily have wallowed in the weepiest clichés and pressed all the tear-jerking buttons, but foregoes them for something subtler and more honestly moving. Here, improbably, we have a comedy about a young man, fit and fastidiously health-conscious, floored by a cancer diagnosis and faced with even odds to survive.

He is Adam (Joseph Gordon-Levitt), a Seattle radio producer who doesn’t smoke, doesn’t drink and jogs in the mornings. (He also recycles, as he's quick to inform his doctor.) Still, he’s troubled by back pain, persistent enough to merit a checkup. The last thing he expects is a potential death sentence, one of those cancers with a name so long he can barely remember it.

“The more syllables it has, the worse it is,” a fellow patient helpfully explains, but Adam, still in shock, hasn’t begun to grasp the ramifications of his illness, physical and otherwise. Much as the chemo wears him down, so too do the pained glances from co-workers, his mother’s hysteria and the discomfort he senses in his girlfriend Rachael (Bryce Dallas Howard).

It’s easy to condemn her as callous, to make her the heavy in screenwriter Will Reiser’s loosely autobiographical tragicomedy. (Reiser, who wrote and produced 50/50, survived a bout with spinal cancer six years ago.) Yet her instinct to flee is at least understandable. Adam needs a caretaker more than a girlfriend, and she’s not up to the task.

If none of this sounds terribly funny, it isn’t – laughter is the therapy Adam needs to dull the pain, to steel himself against the nausea, the exhaustion and the alienation that manifests itself in barely suppressed rage. That’s where best friend Kyle comes in, using Adam’s sickness to pick up girls and generally behaving like a well-meaning clown.

Seth Rogen plays Kyle, and while the part isn’t a stretch from his usual on-screen persona – the casually irresponsible, cheerfully profane stoner buddy – there is a method to his silliness, and real feeling as well. His rapid-fire chatter is often painfully funny, and perfectly in keeping with the movie’s balanced mix of humor and agonizing drama.

That 50/50 resists going maudlin is a minor miracle, and a testament to Gordon-Levitt’s ability to invite sympathy without begging for it, as well as Reiser’s perceptive screenplay, which is tender in all the right places. As Adam heads for surgery, aware that the anesthesia is lulling him into a slumber from which he might never awake, it’s easy to get a little misty-eyed. The movie earns it.