Douglas, husband of British actress Catherine Zeta Jones, is said to be optimistic the treatment will succeed. He will have eight weeks of radiation, and chemotherapy. But the treatment has been known to affect the larynx, said Dr Kenneth Hu of New York's Beth Israel Medical Centre.
"You wouldn't treat a benign tumour with radiation, so most definitely this is a malignant tumour," the Sun quoted Dr Eric Genden, chief of head and neck cancer surgery at Mount Sinai Medical Centre, as saying.
Years of smoking and drinking are thought to have caused the cancer. The Oscar-winner has cancelled all engagements for two months, including promoting new film Wall Street 2: Money Never Sleeps.