One third of people with cancers in the back of the throat (oropharyngeal cancers) are infected with a certain strain of human papillomavirus (HPV), according to new research published in the Journal of Clinical Oncology at the weekend.
The research team, which included Cancer Research UK scientists at the University of Oxford, compared pre-diagnostic blood samples from 938 patients with cancers of the head and neck, oesophageal (gullet) and oropharyngeal cancers with samples from 1,599 people without the disease (the controls).
The HPV family contains nearly 200 strains, but fewer than 10 are linked to cancer, and only one, HPV16, is strongly linked to oropharyngeal cancer.
The researchers tested the blood samples for antibodies against E6, a known HPV16 cancer-causing protein, and found it in over a third of those with oropharyngeal cancers, compared with fewer than 1% of the cancer-free controls.
They found no link with other cancers.
If a person has antibodies to E6, then they are infected with HPV16, and there is a high chance that the cancer-causing process that E6 triggers has been activated.
E6 switches off another protein called p53 that protects cells from DNA damage. Damage to DNA raises the risk of cancer development, which is why p53 is often called the "guardian of the genome".
The researchers say the link between presence of E6 antibodies in the blood and oropharyngeal cancer was independent of time from blood sample to cancer diagnosis.
They could even detect the antibodies to the HPV16 protein in blood samples taken more than 10 years before cancer was diagnosed.
In the UK every year, around 1,500 people find out they have oropharyngeal cancer, and another 470 people die from it.
The researchers estimate about 7% of non-smoking women and 23% of non-smoking men who have E6 in their bloodstream will develop oropharyngeal cancer over 10 years.
Risk of dying within 5 years of cancer diagnosis
But oropharyngeal cancer patients who were infected with HPV16 were more likely to survive than patients whose cancer probably did not arise from HPV infection: the researchers found 84% of infected patients were still alive 5 years after their diagnosis compared with only 58% of uninfected cancer patients.
Study author Dr Ruth Travis, a Cancer Research UK scientist at Oxford, says in a statement:
"These striking results provide some evidence that HPV16 infection may be a significant cause of oropharyngeal cancer."
HPV16 is a major cause of cervical cancer (with HPV18), and is known to spread through genital or oral contact. It also increases the risk for vulval, anal and penile cancers.
While there is a vaccine against infection by HPV16 and HPV18, which is offered to girls aged 12-13 in the UK, we don't know if this also protects against oral HPV infections or oral cancers.
Actor Michael Douglas referred to the link with HPV when interviewed about his own diagnosis with throat cancer.
Sara Hiom, director of health information at Cancer Research UK, says:
"... more research is needed to understand more about HPV infections in the mouth - how they are spread, how easy it is for the body to get rid of them, and what happens when cancer develops - so that we can learn how to reduce the burden of HPV infection in future."Written by Catharine Paddock PhD