HPV Vaccine May Stem Incidence of Throat Cancer

HOUSTON, Aug. 23 -- Human papillomavirus (HPV) infections are likely buoying up oropharyngeal cancer rates while other head and neck cancers decline, researchers said.

Cancer-causing HPV strains have been implicated in half of oropharyngeal cancers, and 90% of HPV-related cases have been pinpointed to HPV-16 in studies, said Erich M. Sturgis, M.D., M.P.H., and Paul M. Cinciripini, M.D., both of the M. D. Anderson Cancer Center here, in a review published online in the journal Cancer.

One of the reasons, the researchers suggested is the "changing sexual practices, such as more frequent oral sex in adolescents and young adults."

To hasten throat cancer's decline, vaccination of boys and and men against oncogenic strains HPV-16 and HPV-18 should be considered, they suggested.

"The current vaccination strategy [suggested for girls and young women ages nine to 26] will only benefit men secondarily as the cohort of vaccinated women age and the incidence of chronic oncogenic HPV infection in the sexually active female population declines," the investigators wrote.

This effect may take a generation to achieve, they said.

To speed up the potential benefit in the prevention of HPV-related oropharyngeal cancers, Drs. Sturgis and Cinciripini recommended "the rapid study of the efficacy and safety of these vaccines in males and, if successful, the recommendation of vaccination in young adult and adolescent males."

Tobacco smoking has been the major cause of head and neck cancers overall. But when smoking prevalence started to slide in the 1970s, the incidence of head and neck cancers took a down turn as well--albeit with a 10 to 15 year delay.

Population age-adjusted incidence of head and neck cancers has been in decline since the mid-1980s while the absolute incidence stopped climbing in 1998 and started up again only in 2006, the researchers said.

HPV type 16 may be responsible for many of the inconsistencies in trends in incidence across age groups and sites within the head and neck region, they noted.

Age-adjusted incidence rates of larynx, oral cavity, and hypopharynx cancer have significantly declined over the last 30 years.

However, oropharyngeal cancer rates have not. This cancer accounts for an increasing percentage of head and neck cancers, now almost as many as occur in the oral cavity and the larynx, Drs. Sturgis and Cinciripini noted.

In one study of oropharyngeal cancer specimens from the Swedish Cancer Registry, HPV-16 prevalence in the cancers increased from 23% in the

1970s to 57% in the 1990s and 68% in this decade, whereas the national smoking prevalence dropped dramatically over the same period.

A case-control study reported in the May 10 New England Journal of Medicine also linked HPV-16 to a 15-fold increase in oropharyngeal cancer risk.

(See: Human Papilloma Virus Linked to Throat Cancer)

"The link between oncogenic HPV and oropharyngeal cancer is quite strong and the majority of the classic criteria of disease causality have been documented by numerous independent investigators," they wrote.

As would be expected for HPV-associated cancer, oropharyngeal cancer sites and younger adults with less tobacco exposure than traditionally seen have been the subgroups with increasing incidence within squamous cell head and neck cancers overall.

The reasons may be limited screening and treatment for precancerous oropharyngeal lesions and an increase in oral sex in adolescents and young adults, the researchers said.

A potential solution is the FDA-approved quadrivalent HPV vaccine Gardasil, which protects against HPV types 6, 11, 16 and 18.

The vaccine was designed primarily to prevent cervical cancer, but it has already proven effective against other cancers related to HPV, including vulval and vaginal cancers.

(See: HPV Vaccine Also Guards Against Vulval and Vaginal Cancer)

Currently, Gardasil is approved only for girls and young women ages nine to 26, and the carryover effect for males is unclear.

"Although we might assume that the current vaccination strategy could prevent HPV-16/18-associated oropharyngeal cancers in women, some data suggest that the overwhelming majority of oropharyngeal cancers in nonsmokers (which are overwhelmingly associated with oncogenic HPV) occur in men," the researchers wrote.

"To hasten the reduction of HPV-16 prevalence in the population, widespread vaccination of adolescent and young adult males should also be considered," they concluded.