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A vaccine routinely used to shield against cervical cancer caused by the human papillomavirus also reduces women's risk of anal cancer, a study published by the journal The Lancet Oncology says.
The trial involved 4,210 healthy women aged 18-25 in Costa Rica, who were randomly assigned the human papillomavirus (HPV) vaccine Cervarix or an ordinary hepatitis A vaccine as a comparison.
Four years later, the women were tested for cervical and anal infections by the 16 and 18 types of HPV, which are notoriously associated with cancer.
Women who received Cervarix had a 76% lower risk of cervical infection and a 62% lower risk of anal infection compared with un-inoculated counterparts.
Anal sex could be anal cancer cause
The protection was even higher in a sub-group of women who most probably had no previous exposure to HPV. In this category, the vaccine was nearly 89% protective against cervical infection by the two viral strains and nearly 84% against anal infections.
Even though anal cancer is rare – just two cases per 100,000 people per year in the overall population, according to some estimates – women generally have twice the incidence of this disease than men.
Why this is so is unclear, although receptive anal intercourse may be a factor.
A condition called cervical neoplasia may also predispose women to the risk of anal HPV infection, regardless of anal intercourse.
Gays a higher risk
Within the general population, higher-risk groups for anal cancer are men who have sex with men. HIV-negative gays have 40 cases per 100,000 individuals per year, and HIV-infected gays 80 per 100,000.
HPV causes most anal cancers, previous research has found. Nearly four out of every five HPV-linked anal cases are caused by types 16 or 18.
In a commentary also carried by The Lancet Oncology, US specialists Diane Harper and Stephen Vierthaler of the University of Missouri-Kansas City School of Medicine, said the cost benefits of HPV vaccination for anal cancer were hazy.
Vaccine efficiency should last for years
The big question was how long the vaccine remained effective, they said.
"Without duration of efficacy of at least 15 years, cancers will not be prevented for women or men who have sex with men, only postponed," the pair noted.
Efficacy trials are lacking and anal cancer incidence is rare. Let's use our resources wisely.
(Sapa, August 2011)
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