Laughter: It’s The Best Medicine in Rogen and Reiser’s ’50/50′ [VIDEO]

In a back booth at Canter’s, Seth Rogen is digging into his matzah ball soup with gusto as his close friend, screenwriter Will Reiser, sips a glass of club soda. In person, Rogen — who has emerged as one of the leading comic actors, writers and producers of his generation — offers up the same rumbling laugh (think a Jewish Santa Claus) and humorous banter as the stoner-slacker characters he plays in such films as “Knocked Up” and “Pineapple Express.”

Reiser, part of Rogen’s “Jew Tang Clan” entertainment posse since the two met on “Da Ali G Show” eight years ago, is quieter and thoughtful, even as he and Rogen seamlessly finish one another’s sentences on this late afternoon.

The same dynamic appears in the best friends who make up the heart of their new movie, “50/50,” which is loosely based on how Reiser’s life and relationships — including his friendship with Rogen — evolved after he was diagnosed with a cancerous tumor of the spine in 2005.

In “50/50,” which is by turns poignant and hilarious, Adam Lerner (Joseph Gordon-Levitt) is a 20-something writer for public radio who has an artist girlfriend (Bryce Dallas Howard) and a pothead-jokester best friend, Kyle (Rogen). But early on, it’s clear all isn’t well with Adam, when he fatigues while jogging and complains of worsening back pain. When Adam finally visits a doctor, the news is shocking: A tumor is snaking alongside his spine, with the almost unpronounceable name of neurofibrosarcoma, or malignant schwannoma. And his MRI — actually based on Reiser’s own MRI — indicates he has only a 50 percent chance of survival. A life-threatening surgery is his only option.

Adam is by nature emotionally repressed and stoic, and as he struggles to come to terms with his cancer, his friends and relatives respond in disparate ways: His girlfriend is unable to deal with the illness and cannot even bring herself to drive Adam to his chemotherapy sessions. Kyle, after an initial freakout, wants to use Adam’s sympathy card to score chicks. Friends say exactly the wrong things, and Adam’s mother (Anjelica Huston) is supportive but smothering.

As Adam’s health deteriorates, help arrives in the form of a novice oncology psychotherapist (Anna Kendrick) assigned to him by the hospital. “She is young and unable to face what she is dealing with — just like Adam — which creates a strong connection between them,” said the film’s director, Jonathan Levine (whose credits include “The Wackness”).

There is levity amid the drama, much of it akin to the raunch-fests-with-heart for which Rogen, and his comedy mentor, Judd Apatow, are known. In the scene where Adam shaves his hair before it can fall out due to chemotherapy, Kyle reveals that his razor has been used on hairs other than from his head. “It’s inevitable, it’s just where my head goes,” Rogen said of the joke.

Online, some individuals have critiqued Rogen for even attempting to make a comedy about cancer, stating that their experience with dying loved ones was anything but funny — some even went so far as to write, “F—- you, Seth Rogen.”

“I’m used to people hating all my s—- before they watch it,” Rogen said. “But I think we did the movie honestly and respectfully and based it on our own experiences.”

Levine, who has helped care for relatives braving cancer, agreed: “It’s not just because I’m Jewish and I own a bong that I relate to this,” he told the producers while lobbying to direct the movie.

“What this film does with character and pushing the boundaries of comedy is incredibly resonant and important. The salient theme is: What does it mean to be young and facing this disease? What does it mean to be facing the end of your life before you’ve really lived it?”

Rogen, 29, and Reiser, 31, met when they were the two youngest staff members on the American version of Sacha Baron Cohen’s “Da Ali G Show.” “I remember feeling threatened that there was another young dude working on the show,” said Rogen, who was recently named by Forbes as “the hardest-working man in Hollywood.”

At the time, Rogen shared an office with his current writing and producing partner, Evan Goldberg (“Superbad”), a friend since being in the same bar mitzvah class at their Reform synagogue in Vancouver, British Columbia.

Reiser, who had his bar mitzvah at a Jewish community center in White Plains, N.Y., remembers being envious of Rogen and Goldberg, who were staff writers while he was an associate producer. “Our office was divided by just a window, so we could see each other all day long,” Reiser said. “In their office, they’d be joking, imitating Sacha’s accents, shouting in Kazakhi [a reference to Baron Cohen’s character of “Borat”] and running back and forth, and I would be on the phone, really stressed out, on the verge of having a nervous breakdown, trying to book guests.”

Rogen and Reiser quickly bonded, however, in part because of their similar ages; they were the only staff members who smoked (both have since quit). Since they couldn’t light up in the show’s skyscraper offices, they’d have to trek down to the parking garage, which provided a nice break from the office intensity. “You needed a reason to leave, and the only reason to leave was to smoke, so we would go smoke cigarettes all the time,” Rogen said.

Reiser, who at 24 was already a workaholic and always the first person in the office at 7:30 a.m., initially dismissed his early cancer symptoms as stress-related. “I had no energy and my knee kept swelling up with fluid,” he recalled. “[Eventually], I could not stay awake, and I was having these horrible night sweats, where I would wake up and my shirt would be drenched, like I had just gone swimming.”

“Your skin just got bad,” Rogen said of the “Ali G” days. “It was like ‘Raiders of the Lost Ark’ when those people were melting. … Will began looking worse and worse, but of course we had no idea how sick he was; we just thought he was working too hard. We’d always joke, ‘The hours are killing him.’ Sacha would say, ‘Should we tell him to go home?’ ”

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“50/50” will premiere at the Toronto International Film Festival on Sept. 12 before opening in theaters on Sept. 30.