This is new stuff for Anna Kendrick - this romance business.

In Up in the Air, she was the chilly new human-resources henchwoman, brought in to ax people by Skype. In the Twilight series, she's Bella Swan's school friend. Love - with a vampire, a werewolf, or mere human - isn't in the picture.

In 50/50, which Kendrick jokingly refers to as "the cancer comedy that no one wanted," the 26-year-old actress is an inexperienced therapist, assigned to counsel a patient played by Joseph Gordon-Levitt. The title refers to his odds of surviving. His girlfriend (Bryce Dallas Howard) isn't handling his illness, or his chemo, well.

And so what begins as a strictly professional relationship turns, well, unprofessional.

"I've never done romantic scenes before," Kendrick says, dropping into Philadelphia recently to talk up the very fine, and, yes, very funny, 50/50, which opened in theaters Friday. "And I knew Joe for precisely 20 minutes before we shot one of the scenes in the car - which is pretty far into our relationship - so I was a little nervous. . . .

"I was just really impressed with the way he could make a person feel like you've known each other for years. . . . I was pretty new to that kind of territory, so I give all credit to him. It made me feel really open. Even though I'd only known him for 20 minutes, he opened his heart to such a degree that you felt really safe - and that's a really tough thing. Actors are pretty sensitive."

The reason Kendrick had just met Gordon-Levitt is that right up until shooting started in the spring of 2010, James McAvoy had the lead role of Adam, the twentysomething Seattleite diagnosed with the Big C. And then McAvoy's wife, actress Anne-Marie Duff, had the nerve to have their baby boy earlier than expected.

"Understandably, James left the production - and Joe came in a little late, so . . . when I came up, it was basically a handshake and 'Are you ready to do this?'

"It was a tough transition, because you get attached to one idea in your head. But when I got on set they had cut together a version of the scene where Joe and Seth Rogen try to go pick up girls, and I just felt like, Oh, this is Joe's movie completely. He owns it."

50/50 is based on a screenplay by Rogen and Will Reiser, the comedy writer who was diagnosed with cancer when he was 24. Kendrick says that the movie, which was first titled I'm With Cancer, and then Live With It, was, as one might expect, a hard sell. Producers and studios weren't exactly lining up to get the thing made.

"Certainly, I wasn't a part of that struggle in any real way, but from what I understand it was not an easy road," she says. "And that completely makes sense. . . . You know, I was just as afraid of the pitch - the 'it's a comedy about cancer' line - as anybody else. It was actually pretty inconvenient that the script was so damn good that I really wanted to be a part of it.

"I just felt like there was such honesty in the characters. I mean, there should be if it's based on a true story. Yet at the same time, there was so much room to play. . . . That's a rare thing, when a character feels really three-dimensional, really honest, and yet you still have the room to make it your own. I was basically told that my character was this really confident, know-it-all young therapist. But when I read it, I thought, you know, that's what you see. I see a really terrified, vulnerable person. And that was exciting to me.

"So, I wonder sometimes when they offered me the job if they were expecting a different performance, but everybody seemed happy with what I did."

Kendrick hails from Portland, Maine. Her first professional job came when she was 12 - on Broadway, as the kid, Dinah, in the 1998 revival of High Society. She was nominated for a Tony Award for her trouble (the second youngest in Tony history). In 2010, she received a best supporting actress Oscar nomination for her work opposite fellow Up in the Air nominees George Clooney and Vera Farmiga. She acknowledges that the role, and the film, were pivotal.

"Of course, Up in the Air was huge for me. The funny thing is - I mean, every job that I've gotten, including 50/50, the director had seen me in Rocket Science. Jason Reitman, the director of Up in the Air, had seen Rocket Science. And that was a film that nobody saw, except for people that are really committed to film, and I'm so grateful for that."

Rocket Science is a charming little 2007 indie, from writer-director Jeffrey Blitz, about a New Jersey high schooler with a stutter who joins the debate team. Kendrick is his ridiculously confident and well-spoken teammate.

"But now, I guess, people think of me from Up in the Air," she adds. "So it's definitely been big. At the same time, I get a lot of offers to do the exact same kind of thing. I get every unfeeling, uptight, ponytailed sister-in-law under the sun - and it's tougher for me to get interest in other things. That's the Catch-22 of it."

Still, she seems to be managing.

Forthcoming from the actress, who now lives in Los Angeles, is Rapturepalooza, a teenage religious apocalypse comedy; The Twilight Saga: Breaking Dawn - Parts I and II, 'nuff said; the ensemble comedy What to Expect When You're Expecting; and End of Watch, a cop drama from Training Day writer David Ayer. In that one, "I am Jake Gyllenhaal's wife," she says, kind of like that's no big deal.

"That was like nothing I had ever done before," she adds. "A lot of it was just shot hand-held - tons of improv. We did this entire trip to Vegas with a crew of maybe five people, including Jake and myself, and we shot the whole way there and this entire night in Vegas and the trip home without a single page of scripted dialogue.

"We just kind of went for it."

Contact movie critic Steven Rea at 215-854-5629 or Read his blog, "On Movies Online," at