August 8, 2013
Dr. David Palma, stands with an X-ray machine at the London Regional Cancer centre in London, Ontario, Aug. 7, 2013. “You don’t have to be promiscuous to get this cancer,” he says.
Researchers say they have found the first direct evidence that the rate of throat cancers linked to the human papillomavirus (HPV) is on a “dramatic” rise in Canada, and will likely pose a major burden to health care for years to come.
The trend seems linked to increased oral sex, especially by men, and is another reason why more effort must be made to improve the lacklustre uptake of the HPV vaccine, say doctors at a London, Ont., hospital.
“The HPV [throat-cancer] epidemic will have tremendous implications for health-care resources,” said their paper, just published in the journal Current Oncology . “These typically younger, healthier patients have a high chance of surviving their disease, and they will have to live with the toxicity of treatment for many decades.”
The sensitive issue came under surprising focus this spring, when actor Michael Douglas suggested in an interview that his throat cancer might have been caused by HPV contracted through oral sex.
Canadian studies released last year concluded that the type of “oro-pharyngeal” cancers — those at the base of the tongue and tonsils — usually associated with the virus have been on the rise, but scientists couldn’t prove a link to HPV. Researchers at London’s Lawson Health Research Institute went a step further, genetically analyzing tumour samples over time to detect changes in the actual presence of the infection.
They found that the number of patients with tonsil cancer, closely linked to human papillomavirus, more than doubled between the mid-1990s and late 2000s, with HPV present in almost three times as many of the most recent cancers.
The risk of contracting a virus-related throat cancer rises with the number of sexual partners, but anyone who has oral sex is at risk, noted Dr. David Palma, a radiation oncologist and co-author of the research.
“Many of the patients we are seeing have only had a few partners,” he said. “You don’t have to be promiscuous to get this cancer.”
The numbers are not huge in relative terms. The rate of oro-pharyngeal cancers rose to 2.6 per 100,000 in 2009, according to a study published last year by the Canadian Partnership Against Cancer.
That would mean about 860 new cases, compared with more than 22,000 new cases each of lung and breast cancer the same year. The throat numbers are expected to keep rising, though, and surpass those of cervical cancer by 2020, said Dr. Palma.
Patients with HPV-related throat tumours stand a good chance of being cured, but can suffer severe treatment side effects, from hearing loss to trouble swallowing and prolonged use of a feeding tube, he noted.
Cancers of the head and neck have in the past usually occurred in elderly people because of heavy smoking and drinking. As the smoking rate has dropped, so too has the overall prevalence of such tumours.
A few years ago, however, physicians started noticing that younger people were contracting cancers at the back of the throat, and suspected HPV was the culprit, said Dr. Palma. Studies have confirmed such a link in the United States and Europe.
To verify that the same was happening here, Dr. Palma, Dr. Anothony Nichols and other colleagues did genetic tests on biopsy samples at the London Health Sciences Centre from 160 tonsil tumors over 18 years, looking for evidence that HPV had been drawn into the cancer’s DNA.
The number of tonsil cancers rose from 32 in 1993-99 to 68 between 2006-11, and the proportion of the tumours positive for HPV jumped to 62% from just 25%.
About three-quarters of the cancer patients were men.
It is likely that the increases are occurring in other Canadian centres, too, the scientists say.
The ballooning caseload would appear to coincide with changes in sexual behaviour that began in the 1970s, as more couples practised oral sex, said Dr. Palma.
Two Canadian epidemiological studies published last year recorded a sharp rise in such throat cancers, but lacked any direct proof of what caused the boom.
The new research, coupled with data from Europe and elsewhere, now provides “quite compelling” evidence that the virus is to blame, said researcher Tonia Forte, co-author of the Canadian Partnership study.
But not everyone is convinced that an HPV-fuelled “epidemic” is emerging.
“The numbers are quite small, and they do vary from year to year, so establishing a trend is not clear,” said Robert Nuttall, head of cancer-control policy at the Canadian Cancer Society.
He did echo calls from the London scientists for wider use of the two HPV vaccines, effective against strains of the virus that cause cervical, oro-pharyngeal, anal, penile, vulva and vagina malignancies.
Canada’s National Advisory Committee on Immunization recommends that both young males and females get vaccinated. Even among school-age girls whose shots are government-funded, however, uptake has been as low as 50%.