Deeply affecting and admirably even-keeled, the cancer drama 50/50 avoids both bitter disconsolation and false inspiration to come up with something that’s honest, clear-eyed and, well, a lot like being there. This authenticity probably comes from the fact that screenwriter Will Reiser based the story on his own life-threatening bout with cancer – though it’s worth noting that “based on a true story” is rarely a guarantee of anything but hyperbole. Joseph Gordon-Levitt plays the Reiser figure, and it’s a richly nuanced performance, one of his best. (The intensity he brings to an operation prep scene is unbearable.) Seth Rogen, a close friend of Reiser’s in real life, is on hand in the best-friend role and has some of his most genuine moments onscreen yet. Somehow all of those involved have managed to avoid the temptation to inflate their experience. Instead, they’ve revisited it in a therapeutic endeavor that actually makes for moving art.