A sexually-transmitted virus that actor Michael Douglas says caused his recent illness only rarely leads to cancer.
In an interview with the Guardian, the Oscar-winner said that his throat cancer was caused by oral sex.
It had been assumed by some that the cancer could have been related to his years of smoking, but the Wall Street and Basic Instinct star said it followed his contraction of HPV (human papillomavirus), a sexually-transmitted virus that is best known as a common cause of cervical cancer, but which can also cause throat cancer.
Asked if he regretted having smoked, the actor told the newspaper: "No. Because without wanting to get too specific, this particular cancer is caused by HPV which actually comes about from cunnilingus.
"I did worry if the stress caused by my son's incarceration didn't help trigger it. But yeah, it's a sexually transmitted disease that causes cancer." He jokingly added: "And if you have it, cunnilingus is also the best cure for it."
According to Cancer Research UK, HPV affects most sexually active people at some stage in their life, but is usually fought off by the immune system without causing harm. It is only on rare occasions that the virus "takes hold", eventually leading to cancer.
About 15 strains of HPV can cause cervical cancer. The most common of these, HPV-16, can also cause oral cancer, though it is not clear how often.
It is also not clear how HPV can end up in the mouth, although some case control studies have suggested it may be through oral sex.
A study released this weekend said there is no need for patients who have developed cancer from an oral HPV infection to refrain from sex with their spouses or long-term partners.
The study found that the spouses of patients with oral cancer caused by HPV did not have a significantly higher risk of developing the disease than the general population.
"Couples who have been together for several years have likely already shared whatever infections they have and no changes in their physical intimacy are needed," said lead author Dr Gypsyamber D'Souza, an epidemiology professor at Johns Hopkins University in the US state of Maryland.
Douglas, 68, who is married to actress Catherine Zeta-Jones, revealed in August 2010 that he had been diagnosed with stage four cancer after a walnut-sized tumour was discovered in his throat.
He underwent chemotherapy and the treatment saw him lose more than 18kg, and left him gaunt and weak.
In March 2011 he said he was confident of having beaten the cancer and he has been clear since then.
He is currently winning rave reviews for his role as Liberace in the film Behind the Candelabra.
Douglas has two children with Zeta-Jones. Cameron Douglas, 34, his son from a previous marriage, was jailed for drugs offences in 2010.