A new study by researchers in the US suggests that the human papillomavirus (HPV) causes as many cases of oral cancer in men as tobacco and alcohol and will overtake the latter within the next ten years. They suggest the main reasons are changes in men’s sexual behaviour and the decline in oral cancers not caused by HPV.
The study is published in the February 1st issue of the Journal of Clinical Oncology and is the work of researchers at the Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, and the Johns Hopkins Medical Institutions, Baltimore, also in Maryland.
HPV is known to cause cervical cancer in women, and there are vaccination programmes in many countries, including the US, to immunize girls and young women against the strains of HPV that are thought to cause over 70 per cent of cervical cancers, for which there are 12,000 new cases and nearly 4,000 deaths in the US alone every year.
Previous research has already shown there is a risk of a range of genital and oral cancers in men also resulting from HPV infection, but as yet there are no immunization programmes for men against HPV.
The only vaccine against HPV is the drug Gardasil, made by Merck & Co. According to an Associated Press (AP) report at the weekend, the drug company will be asking for the US Food and Drug Administration (FDA) to approve the vaccine for boys later this year.
So far, the primary argument for vaccinating men has been to stop the virus spreading to women and cutting down cervical cancer cases. But research on men is catching up, and there is mounting evidence that vaccinating boys will also benefit men directly. Apart from oral cancer, HPV also causes genital warts, penile and anal cancer.
Study co-author, Dr Maura Gillison of Johns Hopkins University, told the AP news agency that:
“We need to start having a discussion about those cancers other than cervical cancer that may be affected in a positive way by the vaccine.”
Gillinson led a study published in May 2007 that suggested people who had oral sex wit 5 or more partners during their lifetime had a much greater chance of having throat cancer and that the cause was most likely to be a well known strain of HPV.
In this new study, Gillinson and colleagues examined nearly 46,000 cases of oral cancer occurring between 1973 and 2004 whose data is held by the National Cancer Institute in nine Surveillance, Epidemiology, and End Results program registries. They split the cases into two groups: those linked to HPV (over 17,500) and those that were not (over 28,000).
The results showed that:
- HPV-related oral cancers were diagnosed at younger ages than HPV-unrelated ones (mean ages at diagnosis were 61.0 and 63.8 years respectively).
- Incidence of HPV-related oral cancers rose significantly from 1973 to 2004, particularly among white, younger men.
- This compared to a stable, unchanging incidence of HPV-unrelated oral cancers from 1973 to 1982, and a declining rate after that.
- Improvements in 2-year survival rates from radiation treatment were more pronounced for HPV-related cancers than HPV-unrelated ones.
The researchers concluded that:
“The proportion of OSCCs that are potentially HPV-related increased in the United States from 1973 to 2004, perhaps as a result of changing sexual behaviors. Recent improvements in survival with radiotherapy may be due in part to a shift in the etiology of OSCCs.”
OSCC stands for oral squamous cell carcinoma, by far the most common form of oral cancer.
According to the AP report, a cause-effect relationship between oral sex and HPV-related cancers is not proven, and some experts have even suggested unwashed hands could also be a risk factor.
Gillinson and colleagues suggested sex was an explanation for the rise in male upper throat cancers. However, HPV-related upper throat cancers has gone down significantly in women in the last 30 years.
There is no evidence to suggest that Gardasil will work in men. Merck are doing a study on the effectiveness of Gardasil for protecting against genital warts, anal and penile cancer in men, but not oral cancers, a Merck spokesperson told the AP, although they will be considering other studies in the future.
It would appear that more studies are needed on the effect of HPV in men, to bring the mountain of evidence up to that already available for its effect on women, and perhaps make the case for male vaccine development equally compelling.
There are about 40 sexually transmitted HPV strains, of which 13 or so are known to cause cancer in men and women. Gardasil does not “cure” infection once it occurs, but it can block 4 of the strains known to cause the vast majority of cervical cancer cases from infecting the body. That is why HPV vaccination programmes are aimed at girls before they become sexually active.
“Incidence Trends for Human Papillomavirus-Related and -Unrelated Oral Squamous Cell Carcinomas in the United States.”
Chaturvedi, Anil K., Engels, Eric A., Anderson, William F., Gillison, Maura L.
Journal of Clinical Oncology, Vol 26, No 4 (February 1), 2008: pp. 612-619.
Sources: journal abstract, Associated Press news report.
Written by: Catharine Paddock, PhD