For writer-director James L. Brooks, that comic tone was always essential when he first began working to adapt Larry McMurtry’s novel of the same name.

His devotion led to a unique challenge: turn a character mentioning “cancer” into a laugh line. In the finished film, he even follows the word’s utterance with a punctuative spit take for good measure.

“It was so important that it be a comedy,” Brooks says. “The word ‘cancer’ then was just — you couldn’t imagine. It was just a word that nobody wanted to say or deal with at that time. It was a bizarre goal. But it was because the picture had to be a comedy to work.”

The instant success was not something that Brooks was expecting. One thread of his third film, the 1994 showbiz satire “I’ll Do Anything,” focuses on the neuroses and pressures of test screenings. It comes from an authentic place through his time working in Hollywood, including on “Terms.”

“We had had a successful test screening that I felt very relieved by. But then we had another one, and they weren’t laughing,” Brooks recalls.

“We were waiting for the scores and I was standing with the head of the studio at the time. There was a very ominous, ‘Let’s go to my office. Let’s discuss this. Let’s see where we are.’ My nerve endings were giving up life. And then the scores came out and they were higher than the previous screening. And suddenly, instead of being on my way to the principal’s office, I was free.”

Brooks shares that the uncertainty of a joke landing haunts him on set “all the time.” Listening to his commentaries, a certain phrase arises a few times: that take after take had to be shot to make the scene “make sense.” Brooks’ heavily stylized dialogue pays off with big laughs and unexpected emotional revelations, but he credits his actors with making what’s on the page sing on screen.

However, the director does push back on a common narrative that has become attached to “Terms of Endearment” — that many scenes, particularly those between MacLaine and Nicholson, diverged from the script.

“There was just a little improv, but there was a lot of being loose,” Brooks says.

Nicholson’s ex-astronaut has-been Garrett Breedlove, who becomes involved (but not quite romantically) with MacLaine’s pent-up grandmother, was not a character in McMurtry’s original novel, instead invented whole-cloth by Brooks.

“James Baldwin, when he had to write a redneck, the thing he was telling himself is, ‘No man is a devil in his own mind.’ Every man is a hero in his own mind. It’s a good thing to think about,” Brooks says.

Brooks employed that mindset in conceiving of Garrett’s climactic cross-country flight to visit Aurora, as she spends her days in a hospital caring for her dying daughter. Is it his astronaut hero complex roaring to the surface? Or is it simply the decent thing to do?

“Shirley has a line where she says, ‘Who would’ve guessed that you were a good guy?’” Brooks says. “I think that’s why he shows up. He wouldn’t have guessed it either.”

Brooks’ following features have fallen all across the spectrum of critical praise — the mean but moving Oscar heavyweight “As Good as It Gets,” the ever-prescient media morality drama “Broadcast News,” the privilege-anxiety doomed romance “Spanglish.” But each invents a tone that’s all its own — a unique achievement that must have some basis in their long gestation periods, written over years as Brooks shepherds other features, like this year’s “Are You There God? It’s Me, Margaret,” or his regular work on “The Simpsons,” which he launched as a producer.

Brooks, who’s 83, is making preparations to direct a new film, his first since the 2010 romantic comedy How Do You Know.

Partnered with 20th Century Studios, the feature, Ella McCay, has courted the similarly named Emma Mackey to star, along with Ayo Edebiri, Jamie Lee Curtis, Woody Harrelson and “Broadcast News” reunion in Albert Brooks.

“We’re going to shoot it. It’s all set to go. We’re going to do it in late January,” Brooks says. “I don’t want to tell you how many years the script took.”