Michael Douglas says his tumor is gone and that he believes it is likely he has beaten throat cancer.
"The odds are, with the tumor gone and what I know about this particular type of cancer, that I've got it beat," Douglas, 66, said in interview with NBC.
The Oscar-winning actor said he has been working on trying to regain the 32 pounds he lost during treatment.
"I'm eating like a pig ... and I've put about 12 back," he said.
Throat cancer can be a devastating illness -- hard to diagnose, hard to treat and especially hard on the body, with the possibility of losing the voice and even the ability to eat, but doctors had said all along that Douglas seemed to have a positive prognosis.
On David Letterman's "Late Show" in September, the actor said his doctors told him he had an 80 percent survival rate from a stage four cancer.
"He is being treated at Manhattan's Memorial Sloan-Kettering Cancer Center," the actor's press representative Allen Burry told ABCNews.com. "The tumor is at the base of his tongue and his doctor's prognosis is for a full recovery."
Doctors say that the optimistic prognosis is rare in throat cancer. If the cancer is associated with smoking and drinking, as the actor suggested his was, survival is usually around 60 percent, but only if caught in earlier stages.
"Mr. Douglas is very curable," said Dr. Kevin Cullen, director of the University of Maryland Greenebaum Cancer Center and a medical oncologist who specializes in head and neck cancer.
The actor told Letterman he had just finished his first week of radiation and chemotherapy after doctors had diagnosed stage four cancer, which Douglas called "very intense." The actor said he had been diagnosed three weeks earlier with cancer above the neck, although the first symptoms of a sore throat appeared earlier this year.
"Typically cancers of the tongue we treat with chemotherapy and radiation. The two are given at the same time," Cullen said.
"Together, it has proven to give a good chance for a cure for the disease," Cullen said. "But it is important to know if it is HPV-related, because those are the cancers that respond well to chemotherapy and radiation and have an excellent prognosis. The ones associated with smoking and drinking respond well, but not as well."
Survival rates for smoking and drinking-related throat cancers are around 50 percent to 60 percent and "the numbers go down from there," according to Cullen.
Those for HPV-related cancers are "higher than 80 percent," he said.
Douglas has said that he had a "walnut-sized" tumor at the base of his tongue.
Treatment Causes Sore Throat and Swallowing Difficulties
Treatment is "manageable," Cullen said. "People get a sore throat and difficulty swallowing and they can also have irritation of the skin and throat from the radiation. But those things get better rapidly after treatment. Over a few months, he would hope to be eating normal food and after six months or more, we usually see someone who looks like they never had an illness."
Three months after treatment, the patient is evaluated to see if the disease is gone. There is a small risk of getting a second primary cancer "down the road," he said.
The worst survival rate is in the hypopharynx, which is a part of the throat area that is involved in the upper digestive tract. There are also three different subsites in the larynx.
Throat cancers are hard to diagnose early because the symptoms are "not specific," according to Dr. Nishant Agrawal, an otolaryngologist and assistant professor at Johns Hopkins University in Baltimore.
"We all get sore throats and take antibiotics and there is some improvement," Agrawal said. "Patients ignore the symptoms and by the time it has developed in the lymph nodes it's stage three or four. That's when most are diagnosed.
"In general, oropharyngeal cancer is usually involved at the base of the tongue and the tonsils and can be associated with HPV, and even at stage four can have an 80 percent cure rate," he said.
The human papillomavirus, or HPV, is the most common sexually transmitted infection in the United States.
Recent studies have found connections between HPV and cancers of the mouth and throat, and recently with lung cancer. Other HPV-related cancers include vulva, vaginal, penile and anal.
HPV has long been known to result in cancers of the sex organs, particularly the cervix. Doctors say men are more prone to throat cancer after kissing or oral sex with an infected partner.
According to a National Institutes of Health website, use of tobacco or alcohol are among the factors that put people at risk of developing throat cancer. Combining tobacco and drinking increases the risk.
'Percentages Are Good,' Douglas Says
Douglas, who has two children with Catherine Zeta-Jones, said he enjoyed the summer traveling with his family before returning to the doctor.
A biopsy found he had late, stage-four cancer, "which is intense, and so they've had to go at it," he told Letterman.
Stage four means that there is lymph node involvement in the cancer. Unlike a breast cancer that has metastasized, throat cancer at this stage is not as widespread.
Cullen said that doctors likely did not operate because chemotherapy and radiation "work very well" with throat cancers. Removing a tumor at the base of the tongue could lead to speech and swallowing problems.
Others who have been diagnosed with throat cancer are writer Christopher Hitchens, who was diagnosed this summer, former Texas Gov. Ann Richards and the late actor Ron Silver.
Throat Cancer Facts
Throat cancer forms in the tissues of the pharynx, the hollow tube inside the neck that starts behind the nose and ends at the top of the windpipe and esophagus. It can include cancer of the nasopharynx (the upper part of the throat behind the nose), the oropharynx (the middle part of the pharynx), and the hypopharynx (the bottom part of the pharynx). Cancer of the larynx (voice box) may also be included as a type of throat cancer.
Most throat cancers are squamous cell carcinomas.
According to the National Cancer Institute, there were 12,720 new cases of laryngeal and 12,660 of pharyngeal in 2010. The estimated annual deaths are 3,600 and 2,410, respectively.
Head and neck cancers account for approximately 3 to 5 percent of all cancers in the United States. These cancers are more common in men and in people over age 50.
Risk factors include tobacco and alcohol use: 85 percent of all head and neck cancers are related to smoking and that risk increases with alcohol use.
Some reports have found that people who smoke and drink are up to 100 times more likely to get head and neck cancer than are people with neither habit.
Other risk factors are the human papilloma virus, a group of about 100 different viruses. The 16 and 18 are associated with throat cancer.