LOS ANGELES (AP) — Michael Douglas is vowing to beat cancer.

The 65-year-old Wall Street star said in an interview with People magazine that he expects to make a full recovery after a walnut-sized tumor was found on the base of his tongue in early August. Douglas is undergoing an eight-week course of radiation and chemotherapy in New York. His doctors said there is no evidence the cancer has spread.

“I’m treating this as a curable disease,” he said. “It’s a fight. I’ll beat this.”

Douglas said Tuesday during an appearance on David Letterman’s Late Show that he had just finished his first week of radiation and chemotherapy.

He said a biopsy found he had late, stage-four cancer, “which is intense, and so they gotta go at it.”

However, Douglas said, the cancer remains above the neck and that means expectations are good, with an 80 percent or better chance of recovery.

The CBS talk-show host told Douglas that his voice didn’t sound like he has throat cancer.

“Because I’m on stage,” Douglas replied.

Douglas’ wife, Catherine Zeta-Jones, told People magazine the most difficult part of the ordeal has been seeing her husband fatigued “because Michael is never tired.” Zeta-Jones, who has two children — Dylan, 10, and Carys, 7 — with Douglas, said she was furious doctors didn’t detect the tumor earlier. Douglas said he spent months seeking a cause for throat and ear pain.

“These things sometimes just don’t show up,” he said.

Besides his medical battle, Douglas is also facing a legal showdown. Lawyers representing the actor and his ex-wife Diandra Douglas are tangling over her claim that she’s entitled to half his earnings from Wall Street: Money Never Sleeps, the Wall Street sequel set to open September 24. Douglas said the lawsuit “kind of came out of left field.”