VANCOUVER - The same sexually transmitted virus that causes cervical cancer is fuelling the growth of some types of oral cancers — and oral sex is believed to be the main conduit, according to experts in B.C. and around the world.
While smoking and heavy alcohol drinking were once the main risk factors for oral cancers, now the human papillomavirus (HPV) has become a more dominant cause as smoking rates wane.
At least one strain of HPV has been identified as the main cause behind the increase in oral cancers — properly called oropharyngeal cancers — in places such as the base of the tongue and around the tonsils, even when they’ve been removed.
The emergence of HPV-caused oral cancers is also attributed to changes in sexual practices over the past three or four decades.
“HPV has been around for ages, but the use of oral contraceptives starting in the 1960s and ’70s led to an increase in incidents of sexually transmitted diseases,” said Dr. John Hay, a radiation oncologist at the BC Cancer Agency, referring to the fact that the pill unleashed more sexual freedom, but that also meant that HPV and other STDs became ubiquitous.
Indeed, up to 80 per cent of sexually active people contract at least one of the 100 subtypes of HPV by the age of 50; in the vast majority, the immune system knocks the virus out. In women, HPV thrives in the cervix and vagina. In gay men, it can wreak havoc in the anal area. In heterosexual men, it becomes established anywhere in the genitalia.
More than 100 cases of oropharyngeal cancers are being diagnosed annually in B.C. In 60 per cent of those oropharyngeal cancers, an HPV infection is confirmed as the cause. As in many jurisdictions around the world, that represents a 50-per-cent increase in the proportion of oral cancers that are HPV-related over the past 10 to 20 years.
Since 2000, the number of HPV-positive oropharyngeal cancers have nearly doubled, from 30 to 60 cases a year in men. In women, the increase has been steady, but less dramatic. The growth in incidence was documented in a recent issue of the journal Cancer by a BCCA research team.
A seminal Swedish study showed that in the 1970s, 23 per cent of oral cancers were HPV-linked. By 2006, the number had climbed to 93 per cent. (A U.S. study recently showed that up to 80 per cent of oral cancer biopsies were HPV positive, a doubling of the proportion in 10 years).
發表於 2010-9-2 09:46
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