A better test for human papillomavirus
By Sharon Gray
A new test for human papillomavirus (HPV) is just as sensitive as the old one, but more specific for detecting cervical cancer, meaning that it has fewer false positive results, according to a study led by researchers at Memorial University.
The results of the study were published in the February 2011 Journal of Clinical Microbiology.
“This is important because reducing false positive results avoids unnecessary additional tests and follow-up, the associated health care costs, and distress to women,” said first author Dr. Sam Ratnam, clinical professor of epidemiology in the Faculty of Medicine at Memorial University and director of the Newfoundland Public Health Laboratory.
HPV infection, he explained, is highly prevalent, but only a small fraction of the infected are at risk of developing HPV-associated cancers.
The study was carried out on 1,418 women in six Canadian centres, including St. John’s, Halifax, Montreal, Thunder Bay, Saskatoon and Calgary.
The investigators report that the new test, called the Aptima HPV test, detected 96.3 per cent of women with high-grade cervical intraepithelial neoplasia or worse (CIN 2+) compared to 94.3 per cent for the old test, the Hybrid Capture 2 DNA test (HC2). Aptima has far fewer false positives than HC2.
“This difference could be attributed to the fact that the Aptima test detects the expression of two oncogenes, E6 and E7, via their messenger RNAs,” said Dr. Ratnam."These proteins are involved in initiation and mediation of oncogenic process that leads to cervical cancer, and to other HPV-associated cancers. The HC2 test, on the other hand, detects the viral DNA which is not as discriminating. The Pap smear, the traditional common screening method for cervical cancer, has few false positives, but fails to detect nearly half of all CIN 2+ cases.”
While HPV is the single most common sexually transmitted virus, its spread is increasing due to rising oral sex among young people, according the Oral Cancer Foundation.
“We're seeing more and more cases of tonsilar cancers in Newfoundland,” a cancer which is frequently caused by HPV, said co-author Dr. Adrian Lear of the Dr. H. Bliss Murphy Cancer Centre, St. John's, Newfoundland.
In people under the age of 50, HPV-associated oral cancers may even be replacing tobacco as the primary causative agent according to the Oral Cancer Foundation.
While the role of HPV is most recognized in cervical cancer, it is also associated with anal and penile cancers, and cancers of the vagina and vulva. The test could detect HPV infections that have begun to progress towards these other HPV-associated cancers, said Dr. Ratnam.
Currently, two vaccines are available against HPV: Gardasil, which is active against four types, 16, 18, 6 and 11, and Cerverix, which is active against two types, 16 and 18. Types 16 and 18 account for about 70 per cent cervical cancer worldwide, and types 6 and 11 account for over 90 per cent of genital warts. These vaccines are now approved in many countries around the world but offered only to females.
“I'm convinced the day is coming when the vaccine will be offered for both males and females through publicly funded programs,” said Dr. Lear.
“Meantime, the use of a more accurate test such as the Aptima test should improve the efficiency and cost-effectiveness of cervical cancer screening around the world, and should help prevent cervical cancer,” said Dr. Ratnam.
The new test is used in Europe but has not yet been approved for use in Canada and the U.S.
“It’s just a matter of time before it is approved,” said Dr. Ratnam.
In addition to Drs. Ratnam and Lear, the other authors on the paper were Francois Coutlee, Dan Fontaine, James Bentley, Nicholas Escott, Prafull Ghatage, Veeresh Gadag, Glen Holloway, Elias Bartellas, Nick Kum and Christopher Giede.