6 February 2012
Massive North American study strengthens case for HPV screening
HPV (human papilloma virus) is a common sexually transmitted virus. Some strains of HPV can cause ano-genital warts. Other strains of HPV can cause cells to develop abnormally and, in some cases, transform into pre-cancer and cancer affecting the following parts of the body:
- cervix and vulva
- mouth, nose and throat
- possibly some cases of skin cancer
HIV infection weakens the immune system and makes people more susceptible to certain cancers. Although treatment for HIV, commonly called ART or HAART, can improve quality of life, lengthen survival and greatly decrease the risk for AIDS-related infections, a heightened risk for some cancers remains among HIV-positive people. In part, this risk persists because despite ART the immune system is unable to completely repair itself. As many HIV-positive people are likely to be co-infected with HPV, their risk for HPV-related cancer, particularly anal cancer, remains elevated.
Research teams across Canada (in Alberta, Ontario and Quebec) and in the U.S. have been collaborating by pooling the health-related data they have collected on HIV-positive and -negative people. This pooled dataset is a powerful tool that allows scientists to explore and understand many health issues that are important when caring for HIV-positive people. This collaboration is called the NA-ACCORD.
The most recent analysis from the NA-ACCORD focused on 34,000 HIV-positive people, comparing their rates of anal cancer with those of 114,000 HIV-negative people. Researchers confirmed the elevated risk for anal cancer among a variety of HIV-positive people, including men who have sex with men (MSM), men who have sex with women (MSW), and women. Rates of anal cancer were increasing over time but then stabilized about a decade ago. Most importantly, the NA-ACCORD team notes that its findings underscore the need to prevent and screen all HIV-positive people for anal cancer. In this CATIE News bulletin we also present some findings from HPV vaccine research.
The NA-ACCORD analysed health-related information from the following populations:
- 34,189 HIV-positive people (55% MSM, 19% MSW and 26% women)
- 114,260 HIV-negative people (90% men, 10% women)
Participants enrolled in the study between 1996 and 2003 and were monitored until they developed anal cancer, withdrew from the study or died, or until December 31, 2007—whichever occurred first. On average, participants were monitored for four years.
The HIV-positive people ranged in age between 30 and 46 years and had about 300 CD4+ cells at the time they entered the study.
Cases of anal cancer occurred during the study period among the following groups:
- HIV-positive MSM – 122 cases of anal cancer among 18,855 men
- HIV-positive MSW – 14 cases of anal cancer among 6,492 men
- HIV-positive women – 15 cases of anal cancer among 8,842 women
- HIV-negative men – 13 cases of anal cancer among 102,607 men
- HIV-negative women – 0 cases of anal cancer among 11,653 women
Among HIV-positive people, this difference between MSM and MSW or women was statistically significant.
In HIV-positive MSM, rates of anal cancer increased from 1996 to 2003. After 2003, the risk of anal cancer remained elevated but stable for this group. A similar pattern was seen for HIV-positive MSW and HIV-positive women.
The importance of prevention
Based on the findings in the present analysis, the NA-ACCORD team called for “enhanced primary and secondary prevention efforts [against anal cancer] among all HIV-infected persons.”
Vaccines for HPV prevention
In high-income countries such as Canada, Australia and the U.S. and in Western Europe, there are two vaccines—Cervarix and Gardasil—that can help prevent infection with strains of HPV (HPV-16, HPV-18). These strains of HPV can cause cervical, vulvar and anal cancer. One of the vaccines, Gardasil, also protects against strains of HPV (HPV-6, HPV-11) that can cause ano-genital warts.
However, it is important to note that both vaccines have mostly been tested in young HIV-negative people who have had few or no sexual partners, and therefore little or no exposure to HPV, and who have not had ano-genital warts or anal or cervical pre-cancer or cancer prior to vaccination.
Would these vaccines provide equal effectiveness among HIV-positive adults who have had considerable exposure to HPV? Researchers are not certain about this and clinical trials are needed to conclusively answer this question. Here is some information on preliminary studies with HPV vaccines among sexually active adults, some of whom have HIV.
Among HIV-positive people
The American National Institutes of Health (NIH) funded an exploratory study of Gardasil among 100 HIV-positive men who did not have a history of pre-cancerous anal lesions or anal cancer. The men in this study were in their mid-40s; their CD4+ counts were around 500 cells and their HIV viral load was less than 10,000 copies. The study team found that Gardasil was safe and did not significantly affect CD4+ counts or HIV viral load. Skin reactions at places where the vaccine was injected were generally mild or moderate.
About 95% of the men developed antibodies against the strains of HPV covered by the vaccine. These antibodies are necessary for attacking HPV. The concentrations of antibodies produced in these men were lower than reported in some studies of HIV-negative people. For instance, their concentration of antibodies against HPV-16 was about 50% less than seen in HIV-negative women between the ages of 34 and 45 years, and 40% less than found in HIV-negative women between the ages of 16 and 26. However, the concentration of antibodies was similar to that seen in HIV-negative MSM between the ages of 16 and 26 who had been vaccinated with Gardasil.
HIV-positive men who were taking ART in this study had greater concentrations of antibodies to HPV as a result of the vaccine than men who were not using ART.
The U.S. researchers encourage further studies of HPV vaccines in HIV-positive men who are regularly screened for abnormal anal growths and anal cancer.
In Canada, researchers are exploring the effect of HPV vaccination among HIV-positive girls and women in a trial called CTN 236. For further information about this study, visit the Canadian HIV Trials Network site.
Among sexually active HIV-negative men
Doctors at New York City’s Mt. Sinai School of Medicine conducted an observational study of 202 HIV-negative MSM, all of whom had biopsy-proven pre-cancerous anal lesions caused by HPV infection. The men were between 20 and 79 years of age. After diagnosis and treatment of anal lesions, all the men were offered vaccination with Gardasil, but only some chose to receive it. After about two years of monitoring, researchers found that 14% of vaccinated men and 31% of unvaccinated men had a recurrence of precancerous anal lesions.
Note that observational studies cannot by their nature produce definitive results. In this particular case, the study cannot prove that vaccination with Gardasil reduced the risk of pre-cancerous growths recurring in some men. Such a conclusion may be reached from a randomized, controlled clinical trial, which the Mt. Sinai researchers encourage.
Preventing anal cancer
Ideally, young people of both genders should receive HPV vaccination. Until well-designed clinical trials are conducted, it is not clear how effective HPV vaccines will be at preventing abnormal anal growths, pre-cancer and anal cancer in HIV-positive people.
In the meantime, anal cancer screening programs may be available in some larger cities. Often such programs are funded as part of research studies and may not be the standard of care. The results of the NA-ACCORD’s recent analysis show that all HIV-positive people, particularly MSM, need anal cancer screening.
A final note: Among sexually active men, correct and consistent use of condoms offers some protection from (re)infection with HPV and many other sexually transmitted infections, including HIV.
We thank Marc Steben MD for his expert review and helpful comments.
—Sean R. Hosein
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