Image caption There are more than 100 types of HPV

One third of people diagnosed with throat cancer are infected with a form of the HPV virus, a study suggests.

HPV (human papillomavirus) is the major cause of cervical cancer, and the virus is known to spread through genital or oral contact.

Actor Michael Douglas is reported to have spoken about the link after his own diagnosis with throat cancer.

Experts said this study in the Journal of Clinical Oncology, which quantifies the link, showed "striking" results.

There are more than 100 types of HPV. Most people will be infected with HPV at some point, but in most the immune system will offer protection.

There are two HPV strains which are most likely to cause cancer - HPV-16 and HPV-18.

HPV-16 is thought to be responsible for around 60% of cervical cancers, 80% of cancers in the anus and 60% of oral cancers.

Around 1,500 people are diagnosed with throat cancers each year in the UK, with around 470 people dying from the disease.

Survival benefit

This study looked at HPV's link with cancer of the back of the throat - oropharyngeal cancer.

It looked at blood test results collected from people who took part in a huge prospective study into lifestyle and cancer, who were all healthy at the start.

Everyone gives a blood sample when they join the study, and in this case the researchers were able to check for the presence of antibodies to one of HPV's key proteins - E6.

Condoms won't stop infections completely."

E6 knocks out part of cells' protection system, which should prevent cancer developing.

Having the antibodies means HPV has already overcome that defence and caused cancerous changes in cells.

The researchers compared blood test results - some more than 10 years old - for 135 people who went on to develop throat cancer and for 1,599 cancer-free people.

The University of Oxford team found 35% of those with throat cancer had the antibodies, compared with fewer than 1% of those who were cancer-free.

However, these patients were more likely to survive throat cancer than people whose disease had other causes, such as alcohol or tobacco use.

The study found 84% of people with the antibodies were still alive five years after diagnosis, compared with 58% of those without.

Broader effect?

Dr Ruth Travis, a Cancer Research UK scientist at Oxford who worked on the study, said: "These striking results provide some evidence that HPV-16 infection may be a significant cause of oropharyngeal cancer."

Sara Hiom, Cancer Research UK's director of health information, said: "HPV is an extremely common virus.

"Practising safer sex may reduce the risk of getting or passing on HPV, but condoms won't stop infections completely."

She added: "If the HPV vaccine can also protect against oral HPV infections and cancers, then it could have a broader potential protective effect, but we don't have enough research yet to tell us. "