"What now?" asks a character near the end of "50/50," a beautifully written, achingly truthful slice-of-life directed by Jonathan Levine (2008's "The Wackness"). Isn't that always the question? Whether we're changing jobs, walking away from or starting a relationship, moving to a new town, or simply figuring out what to do in any given minute, our lives are forever evolving in big ways and small as we make decisions about what our immediate future holds. We assume there is always going to be another moment to experience, after all, because the alternative is frightening and nearly inconceivable. It is this unimaginable flipside that 27-year-old Adam (Joseph Gordon-Levitt) has no choice but to face head-on when he goes to the doctor about an aching back and walks out with the grave news that he has neurofibrosarcoma, a form of cancer affecting the nerve tissue around his spine. His doctor uses long, daunting words that might as well be another language, so Adam researches the disease himself and learns there's a 50/50 chance of survival. If this sounds like the set-up for a maudlin, manipulative mess of a melodrama, think again. Levine is far too savvy to let the film waver into soapy, TV-movie territory, and he's got an exceptionally strong screenplay by Will Reiser to work from. Reiser, who fought his own battle with cancer in his twenties and fortunately won, knows his way around this subject. He and producing partner/friend Seth Rogen weren't about to create a dishonest story out of their true-life happenings, and it is this firsthand familiarity that ensures the picture's drive, vitality, natural humor and ultimate poignance.

Seattle Public Radio writer Adam exercises regularly, doesn't smoke or use drugs, and generally lives his life on the straight and narrow. He's not even thirty yet and should be a beacon of health, which makes it all the more unexpected when he discovers he has a malignant tumor and will require chemotherapy to try and beat it. Adam is shocked at first, then increasingly numb. His artist girlfriend Rachael (Bryce Dallas Howard) agrees to stand by him, but it's obvious how ill-equipped she is to handle it. Mother Diane (Anjelica Huston), who is already coping with a husband suffering from Alzheimer's, wants to be supportive but tends to smother and overreact, which is why Adam was hesitant to tell her in the first place ("Have you ever seen 'Terms of Endearment'?" is how he initially broaches the topic to her). As for best friend Kyle (Seth Rogen), he masks his own fears and confusion by trying to make light of a tough situation. He certainly doesn't mind the medicinal marijuana his pal procures, either. Feeling alone—no one he knows can fully understand what he's going through—Adam gradually finds some solace in his emerging friendship with Katie (Anna Kendrick), a young therapist whose inexperience is matched by her heart. He doesn't exactly make her job any easier, but she listens to him and sees through his stoic façade in a way that no one else seems to. That may be just what he needs as his intense treatments start to take a toll on him and he confronts the very sobering possibility that this might be one fight he doesn't win.

With no stereotypes to speak of and very few contrivances, "50/50" is an uncompromising gem, the kind of film that hits all the right notes as it navigates from gentle, unforced humor to knowing pathos. Usually in movies with tearjerker leanings, one can sense the wheels of superficial calculation squeaking along, but director Jonathan Levine trusts in the reality and urgency of the situation and the sympathetic clarity of his characters to more effortlessly bring emotion to the proceedings. It is so refreshing when a studio picture doesn't feel the need to pander to its viewers with lots of sudsy string-laden music and falsely fabricated conflicts. What Adam is facing himself, and how, by extension, his friends, family and close acquaintances deal with it in their own way is all the conflict needed. Mistakes are made along the way—Adam shuts his mother out and doesn't stop to think about how lonely her life must be taking care of his ailing father, a fact that Katie astutely calls him out on; Rachael is caught cheating on Adam even as she comes home to him every night; Kyle deflects in order to avoid really tackling the gravity of Adam's circumstance—but in those flaws are believable, accurately felt three-dimensional people.

Over the last twenty years or so, Joseph Gordon-Levitt (2011's "Hesher") has been racking up a résumé impressive enough to make the vast majority of his acting peers jealous. He's a chameleon no matter the role, and his enormously moving work here as Adam should finally earn him the awards acknowledgment he so wholly deserves. The viewer is by Adam's side from moment one, as he jogs through Seattle and pauses to wait for the "walking" signal on a deserted city street. Even when he frustrates, shutting off what he's going through or failing to call his mom back, it is acknowledged and understood, a part of his necessary personal growth. Most of all, Gordon-Levitt makes certain that Adam becomes real rather than a writing construct so that what he goes through means more than it otherwise would on screen. In scenes ranging from a much-needed conversation he has with his mom where he asks her how she is, to an explosion of pent-up emotion in Kyle's car that suddenly turns the movie's one over-the-top instance into one of its most harrowingly candid, to an intimate phone call he makes to Katie the night before his surgery, Gordon-Levitt—and the film—remarkably keep resetting the bar.

In her first role to live up to the one she was Oscar-nominated for, Anna Kendrick (2009's "Up in the Air") is nothing short of lovely as Katie, a 24-year-old therapist still studying for her doctorate who takes on Adam as her third patient. Katie has been taught all the tricks of her trade and follows them to the letter without having fully grown comfortable in her role (her attempts to comfort Adam by awkwardly patting his arm is a recurring source of amusement, and a telling detail about where she stands in her professional experience). Beyond that, though, Katie just wants to help people in any way she can, and it is this raw passion and endearing personality—she keeps catching herself saying more than she should about her own myriad troubles—that Adam notices and likes about her. Kendrick is attentive to the details and quirks of her character, and just plain wonderful besides. She's a treat to watch.

As Adam's protective mother Diane, Anjelica Huston (2010's "When in Rome") gets a more down-to-earth part than she's accustomed to, and it suits her well; her relationship with her son is one of the film's most touching aspects. Bryce Dallas Howard (2011's "The Help") has a tough assignment as Rachael, Adam's girlfriend, particularly once it comes to light that she hasn't been forthcoming about her extracurricular activities while shuttling him off to his doctor's appointments. It would be easy to treat Rachael as an irredeemable bad guy—and she is two-faced—but she at least cares enough about Adam that she doesn't want to abandon him. "You have no idea how stressful it's been for me," Rachael tries to explain to him, not stopping to think how many times over it must be stressful for the person who actually has cancer. Howard nicely turns a role that could have been thankless into one that makes an impact. Finally, Seth Rogen (2011's "The Green Hornet") fulfills the requirements of best friend Kyle perhaps too convincingly. Kyle, a pot-smoking, skirt-chasing jokester, is archetypically Rogen—and since the role was based on him, no wonder—though it doesn't give him much chance to stretch. Even when he nears annoyance, the actor is faithful to who he's playing, and the goodness inside him. At least in the annals of Rogen's cancer-based comedies, this one is superior in every way to 2009's overlong, unfocused "Funny People."

"50/50" is deep and universal, not about cancer per se (though it is insightful on this topic as well), but about the unexplainable forces in life that are so much bigger than ourselves. After Adam has shaved all his hair off, Kyle becomes convinced his sickness will attract women and get him more sex. Adam is curious to put this theory to the test, but even the most well-meaning of ideas sometimes don't meet expectations. Leave it to one's own mortality to put what's—and who's—really important into perspective. With a make-or-break, potentially even life-or-death surgery staring back at him, Adam gazes out at a world that he soon may no longer be in. He's scared, of course, and angry about it, but there's also a nagging feeling that he hasn't had the time to do what he wanted to do and see what he wanted to see. Time, as the old adage goes, waits for no man, and "50/50" braves and explores this notion with a thoughtful, heartbreaking levity.