The drawl, the shock of unruly white hair and scraggly beard can lead to the wrong first impression of Jim Allison.

Learning that this Texan, a lifelong blues harp player and committed Willie Nelson fan, has been known to close down his share of honky tonks cements it.

This “sumbitch,” as they say down yonder, is “Just another Texas s—kicker.”

But this salty Texan has fought his share of battles over Creationism intruding into the state’s science curriculum. This UT alumnus has run experiments in labs from Austin to Berkeley to the Scripps Institite.

This s–tkicker has a Nobel Prize in Physiology or Medicine. That’s because this sumbitch has come up with a cure for cancer.

“Jim Allison: Breakthrough” tracks Allison’s long career and his solitary path from research to immunotherapy drugs that in many patients, cure cancer.

The film is a portait in dogeddness and going against the current thinking in cancer treatment and research.

Allison lost his mother to cancer, and a family predisposition to the disease helped drive him.

“You ought to at least do something that helps people.”

As he immersed himself in the world of the newly-discovered (while he was in college) “T-cell” antibodies the human body uses to fight disease, and turned that research towards getting T-cells to fight tumors, he was swimming against a flood and the tide of cancer treatment history.

“Breakthrough” reminds us of another big “cure for cancer” using the immune system. Interferon wasn’t a complete bust, but the 1980s “cure” was a significant letdown, in terms of what was promised and what actually resulted.

Still, Allison pushed on, challenging other research, sticking with immunotherapy at the T-cell receptor (molecular) level. He is an iconoclast, colleagues — some of them competitors — say. “Stubborn” is a word they avoid. Not that his brother Murphy does.

“Diamond Head” he was nicknamed, Murphy Allison jokes. Jim’s skull is “the hardest substance known to man.”

He had to be hard-headed. One of Allison’s scientific peers from the world of “peer reviewed science” marvels that “the skepticism was widespread, and Jim experienced it every day.”

That didn’t stop when he and his colleagues had their breakthrough. He had to then turn over his life to finding a company to polish the discovery of something that worked in cancerous mice into a drug fit for human trial. He had to convince Big Pharma to get behind a corner of the field that they had been leery of since Interferon.

Documentarian Bill Haney (“The Price of Sugar”) also tells the story of Sharon Belvin, diagnosed with melanoma at 22, and one of the first people to benefit from the unusually long clinical trial it took for Allison’s “breakthrough” to show results. Her story adds flesh and blood to the cold chalkboard science.

And as a sidebar, Haney — through narrator Woody Harrelson and others — recalls Allison’s early efforts to fend off the intrusion of non-scientific “Creation Science” from being introduced into the Texas curriculum.

The flinty Allison’s blunt, dispassionate take-down could be a model for a two sentence end to that debate.

The film’s third act tracks patient-Blevin’s experiences and the history of Ipilimumab, the antibody Allison’s work developed and got to market — a near-run thing that took years and years.

Some cancer patients survived long enough to have it there for them in their darkest hour. Others did not. The film isn’t great at building suspense, and like the FDA approval process it summarizes, hits a point where it drags a bit.

And whatever the thrills of a call from Sweden might bring, the fact that Woody Harrelson narrates this and Willie Nelson has been mentioned should tip you to a Big Moment that surpasses the Nobel in the finale.

Did I mention Allison’s from Texas?

MPAA Rating: PG-13 for thematic material and brief strong language.

Cast: Jim Allison, Sharon Belvin, Dr. Jedd Wolchock, Malinda Allison, Dr. Max Krummel, Eric Benson, Andrew Pollack, narrated by Woody Harrelson

Credits: Directed by Bill Haney. A Dada Films release.

Running time: 1:29