09/27/2011 01:40 pm ET Updated Nov 27, 2011

Anna Kendrick Injects Herself Into '50/50' Character

Though "50/50" is just loosely based on writer Will Reiser's experience navigating cancer in his mid-20s, nearly every character in the movie is based on a real person who was involved in Reiser's life during that confusing time. Most prominently, Seth Rogen, Reiser's best friend and co-writer, plays a twisted version of himself, while Joseph Gordon-Levitt plays Adam, a fictionalized big screen Reiser.

Anna Kendrick, on the other hand, takes on one of the few major roles in the film with no true backstory. But that hardly means that she didn't find a way to inject life into her character.

Kendrick plays Katherine, a 24-year-old psychotherapy graduate student who is charged with somehow comforting a terse, scared -- and three years her senior -- Adam. Hot on the role from the moment she read the script, Kendrick said she felt a certain empathy with Katherine from the start.

'[She] was such a mess. She was so vulnerable and terrified on the inside. I liked that a lot," Kendrick told The Huffington Post in an interview on Monday. "I felt like a lot of people didn't see that, and maybe that's because I projected some of that on to the character, I guess I'll never really know."

Reiser, she said, didn't quite realize the extent to which they could mine Katherine's background and dialogue for compassion, palpable fear and professional uncertainty. Instead, the initial version of the script envisioned the character as the apathetic daughter of a well-regarded therapist, thrust into the field without any sort of enthusiasm or desire to help her patients. Unable to reconcile that with what she saw on paper, Kendrick revealed that she spoke to the film's director, Jonathan Levine, about making a major change.

Since the character was untethered to reality or responsibility to someone else's truth, the filmmaker was able to tell Kendrick to rebuild Katherine in her vision, a much welcomed instruction.

"So I think it was great to be able to say, 'I think this is a girl who has great instincts, really listens, all of her friends really came to her for advice, and she will be a good therapist one day,'" Kendrick said, "'but right now she's so nervous and she's trying too hard to say what she's supposed to say and to sound like what she thinks a grownup should sound like, but she's really ineffective.'"

Kendrick's version of Katherine tries to play it by the book with Adam, if only because, working with just her third patient, the textbook's recommended treatment techniques are really all she knows. From the start, Adam undermines and belittles her, taking out his fear and frustration on the polite young therapist. She does her best to convince him to trust her -- a difficult task, given that she doesn't fully trust herself -- and in the process, develops a relationship with him based more on their mutual uncertainty than on any sort of traditional healing.

"I liked the idea of a young therapist," Reiser told The Huffington Post in a conversation earlier this month, "because I think it just shows how that at age, from all different points of view, how difficult it is to deal with something like this and you have all these young characters who are all kind of beginners, you know, no one quite knows how to deal with it."

Gordon-Levitt was able to channel Reiser's uncertainty to inform his role; Kendrick, on the other hand, had no exact insight into the life of a beginning doctor, but did have other real life experiences that helped her fill in the blanks.

"I feel like maybe part of the reason I projected so much of my anxiety on to her was because of what I was going through at the time, which was Oscar season," she remembered, referring back to the rush of press that came with her Best Supporting Actress nomination for her role in "Up In The Air," the 2009 Jason Reitman film starring George Clooney.

"When I met with Jonathan for the first time, I was so kind of discombobulated and I felt that I couldn't really form complete thoughts that I think, as we were leaving that meeting, I think I said to him something along the lines of, 'Please still hire me, I promise I'm not crazy,'" she laughed.

With "50/50" set for a Friday release, Kendrick is excited, if not a little nervous for the public's reaction. Making a bad cancer comedy, after all, could be fatal.

"I guess we always worried that, if you're not honest, the humor will feel inappropriate," she admitted. "So I guess we just tried to keep everything really honest. I feel like I'm nervous for the moment when a therapist comes up to me and says, 'That was unbelievable and no one is that bad.'"

Sounds like a familiar worry; looks like the character was pretty autobiographical, after all.