“There was a knot on the left side of my neck. I noticed it about a year before I was diagnosed," Paulsen tells Heat Vision in his first wide-ranging interview about his diagnosis. "When I went in for my yearly physical, my doctor felt it and said, ‘That’s not good.’ I thought he was screwing with me because I’d known him forever. But within two weeks, I was diagnosed with Stage 3 metastatic squamous cell carcinoma with occult primary. What that means is, the lump on my neck was cancer that had migrated from another area and the doctors didn’t know where that was.”

The doctors took several throat biopsies that still haunt Paulsen.

“I grew up playing hockey, I’ve had my nose busted and teeth knocked out, but those biopsies…they really got my attention," he says.

Paulsen was nervous about the treatment’s impact on his voice, as he is the sole breadwinner for his family.

"My livelihood depends on me speaking. They told me the treatment would kick my ass, and they weren’t sure what effect the radiation would have on my vocal cords," Paulsen says.

There was a moment when he considered delaying treatment because the cancer was slow-moving, but the doctors advised against it.

"If we don’t do this now and start treatment, you’re going to end up like Roger Ebert," his doctors told him, referencing the late film critic who died of cancer in 2013.

So, Paulsen moved forward, full steam ahead.

To understand Paulsen's tenacity in fighting cancer, one must look back to his roots and the drive that brought him to Hollywood.

Rob Paulsen got his showbiz start as the vocalist for a classic rock cover band. They toured the Michigan circuit in the late 1970s.

“We were really good for a bunch of local musicians. Our original music was awful but we were great at covers. It was a sweet gig, we made $250 bucks a week. I still lived with my parents but I owned a brand-new Honda Civic," he recalls.

Paulsen knew that he wanted more, but it took an inebriated fan to put things in perspective.

“I remember this guy, Mickey, he would scream the songs with a Heineken in each hand. After the show, he said, ‘You guys are unbelievable. You’re the best band in Flint!’ At that moment, something inside me said, ‘He’s right, this is it. You’re 21 and if you stay here, this is it for you,' " recalls Paulsen.

Within 30 days, Paulsen said his goodbyes and left for Hollywood. His drive for success was bigger than his desire for a comfort zone.

Paulsen’s first lead role was as Hadji, the Indian character on the Jonny Quest reboot, but what really launched his career was Teenage Mutant Ninja Turtles, which cast him as Raphael in June 1987. The show would become a phenomenon, accounting for untold millions in merchandising sales. Its success led to a string of starring roles in Mighty Max, The Mask, The Tick, and Animaniacs

“If Turtles changed my career, Animaniacs changed my life," he says of the groundbreaking show, which ran from 1993-98.

Paulsen lent his voice to Yakko Warner, Dr. Otto Scratchensniff, and the lovable but dimwitted mouse Pinky (Narf!). Originally, Paulsen wasn’t a shoo-in for the parts. As he recalls, it was a bold move that got him the roles.

“When I first auditioned for the show, I went up to the show’s producers, who I knew from Tiny Toons. I said, ‘If you don’t hire me for this, you’re making a mistake.’ I wasn’t trying to be arrogant, I just knew this was something I could do really well. I can kill this," he says.

Animaniacs allowed Paulsen to showcase his singing abilities, from the opening theme song to “Yakko’s World.” The show’s musical numbers were so popular that Paulsen decided to license the music from Speilberg and Warner Bros. and take his co-stars on the road to perform the songs with either piano backing or a full orchestra for the Animaniacs live tour.

All of that could have gone away with his cancer diagnosis, but he fought it hard.

Paulsen received daily radiation and chemotherapy for seven weeks. He lost 50 pounds, the function of his salivary glands and the ability to taste food.

“I could be eating cardboard or a ball of yarn, I couldn’t tell the difference. That’s a quality of life thing that’s a drag, but I’m hopeful that some of it will come back," says Paulsen. "They said I won’t be 100 percent for two years, so I’ve still got a year to go. It could’ve been a lot worse.… I spend a lot of time with sick kids and terminally ill fans. I’ve seen what they go through. I’m very lucky and blessed.”

Paulsen was relieved when his post-treatment voice proved indistinguishable from his earlier work. His latest scans show no cancer and he’s been back to work as Donatello on the newest incarnation of Nickelodeon's Teenage Mutant Ninja Turtles.

As for the future, the voice actor is excited about the possibility of an Animaniacs reboot, which he has had early discussions on. He's also teamed with the Nerdist to stream his Talkin’ Toons podcast on Project Alpha.

And he's also thankful his role wasn't recast during the months his cancer kept him from the recording booth.

“Dreamworks, Nickelodeon, and Disney could have easily replaced me, but they saved my jobs until I was able to go back to work. I can’t say enough about how kind they’ve been to me," he says.