More than three times as many men than women in the U.S. have oral infections with human papillomavirus (HPV), a virus responsible for causing 31,500 new cancers every year, found a new study. And the HPV strain responsible for the vast majority of HPV-related cancers in the U.S. occurred orally six times more often in men than in women, researchers learned.
“Most surprisingly, we found that oral HPV infection prevalence among men with concurrent genital HPV increases with age, while this trend reverses among women,” said the study’s senior author, Ashish Deshmukh, PhD, MPH, an assistant professor of public health at the University of Florida in Gainesville. It’s not clear why men with genital HPV infections would be more likely to develop oral HPV as they get older when women’s risk drops with age.
The research, funded by the National Cancer Institute, found that an estimated 11.5 million men and 3.2 million women have oral HPV infections at any given time. The highest risk strain, HPV-16, was found in 1.8% of men and 0.3% of women between ages 18-69, equivalent to approximately 1.7 million men and 270,000 women.
HPV is the most common virus transmitted through intimate or sexual contact. Nearly all people who have been sexually active have had an HPV infection. Most HPV infections clear on their own without any symptoms, but several strains can develop into cancer. An estimated 3% of U.S. women’s cancer cases and 2% of all U.S. men’s cancer cases are caused by high-risk HPV.
The virus causes nearly all cervical cancer as well as 95% of anal cancers, at least half of all vaginal and vulvar cancers and about a third of penile cancers. One of the fastest growing types of HPV-related cancer is oropharyngeal cancer, which occurs at the back of the throat. HPV causes about 70% of all oropharyngeal cancers in the U.S., and these are the cancers most likely to develop from oral HPV, especially strain HPV-16.
From 2008-2012, approximately 12,600 men and 3,100 women were diagnosed with oropharyngeal squamous cell cancer caused by HPV.
The researchers analyzed findings from 4,493 men and 4,641 women, ages 18-69, who participated in the 2011-2014 National Health and Nutritional Examination Survey (NHANES), run by the Centers for Disease Control and Prevention. Specimens were collected from each participant through an oral rinse and either a penile or vaginal swab.
Analyses of the specimens revealed that 11.5% of men had an oral HPV infection, more than three times as many as the 3.2% women who did. Men were also more likely to have a high-risk strain of HPV: 7.3% of men compared to 1.4% of women.
About one in five men who had at least two male oral sex partners had a high-risk HPV infection, and men with a genital HPV infection were four times more likely to have oral HPV than men without a genital infection.
Scientists don’t yet know why men’s rates of oral HPV would be so much higher than women’s, but Deshmukh offered some possibilities.
“Studies show that HPV persists longer among men, and that might be causing increased prevalence,” he said. “It is also possible that men acquire oral HPV more readily than women.”
Another possibility, Deshmukh said, is that men are less likely than women to develop an immunity against HPV after a genital HPV infection. If that is occurring, women would have “greater protection against subsequent oral HPV infection,” he said.
All of these speculations, however, are just that: speculations without enough evidence to suggest which scenarios may be actually occurring.
The two main ways to protect against HPV infection are getting both doses of the HPV vaccine and using condoms, though condoms cannot fully prevent transmission. The HPV vaccine, currently recommended for all 11- and 12-year olds, is available for men through age 21, or through age 26 for men who are gay or bisexual, who have sex with men or who have HIV or otherwise weakened immune systems. Studies have found the vaccine responsible for big drops in HPV infections among females.
“Our study shows that oral HPV infection prevalence was lower among eligible boys who reported receiving the 4-valent vaccine,” Deshmukh said. The 4-valent vaccine is Gardasil, which protects against four high-risk strains of HPV. Today, a 9-valent version of Gardasil is available that protects against nine high-risk strains of HPV and thereby can prevent 90% of HPV-caused cancers.
“Thus, although, no evidence exists on cause-effect relationship on efficacy of HPV vaccine,” Deshmukh said, “early evidence from our study show that vaccine might potentially prevent oropharyngeal squamous cell cancer.”
Researcher disclosures: Three of the study's authors, Dr. Timothy Wilkin, Dr. Andrew Sikora and Dr. Jagpreet Chhatwal, have consulted for and/or received research funding from an industry source.