Attacking From the Rear

Each year, approximately 5.5 million Americans are infected with human papillomavirus, which is responsible for most genital warts and accounts for about one third of all STD diagnoses. Approximately 75% of sexually active adults in this country eventually become infected with genital HPV. For most of them, an antibody-mediated immune response will clear the virus. But in others, the virus evades the immune system. It can remain latent in skin cells about five layers under the surface or become active--producing warts or precancerous cells. This is especially common in the anal canal, where HPV can be present for decades. Since HPV causes cancer in the anal canal just as it does in the cervix, physicians are now seeing a parallel rise in the incidence of anal cancer. It's estimated that there will be about 4,650 cases of anal cancer this year (compared to 10,000 cases of cervical cancer). This works out to about 1.6 cases per 100,000 men and 1.8 cases per 100,000 women--twice the rate of 10 years ago. If you look at men who have sex with men, the incidence of anal cancer is 35 cases per 100,000, which is equal to the incidence of cervical cancer before the age of regular Pap smear screening. In HIV-positive men who have sex with men, the incidence rate jumps to 80 per 100,000. These numbers indicate that we need to renew our efforts to regularly screen for HPV with anal Pap smears. The test is administered by inserting a small, soft brush or swab into the anal canal to collect cells that are then studied by a pathologist--exactly the same way cervical Paps are done. The pathologist grades the cells from normal to atypical to low-grade changes to high-grade changes. When severe changes occur, patients are referred for a high-resolution anoscopy--a procedure that examines the rectum under magnification to identify areas that need to be biopsied. If early cancer cells are found and treated, we can prevent the need for aggressive treatments with radiation or chemotherapy and avoid their painful side effects. Ultimately, lives can be saved. Almost 90% of gay and bisexual HIVers have HPV in their anal Pap results, versus 60% of HIV-negative men. Among HIV-positive women, 70% have anal HPV, versus 42% of HIV-negative women--a higher rate than that found in cervical Paps. This even holds true for women who say they have never engaged in anal intercourse--the thought being that HPV can migrate from the vagina to the rectum via fingers or toys. Fortunately, most people with anal HPV will not progress from low- to high-risk, and only a small percentage will progress to cancer. As expected, progression is more likely in people with high viral loads and low CD4 counts. Unfortunately, the use of combination antiretroviral therapy does not cause any regression in the severity of precancerous changes. Counterintuitively, there is concern that the prolongation of life by antiretroviral therapy might provide an opportunity for more anal cancers to occur--with prevalence as high as 5% among HIV-positive men who have sex with men with high-grade lesions. Experts in the field are now recommending anal Paps yearly, although the Centers for Disease Control and Prevention has not established formal guidelines. Technology also exists to serotype HPV strains found on Pap smears. There are about 200 strains of HPV, with 20 found in the genital tract. While there is less agreement among HIV treatment providers about the usefulness of serotyping, some argue that patients with high-risk strains should be followed more closely. Condoms can prevent some transmission of HPV, but because the virus can be found farther down the shaft of the penis than a condom can cover and on vulvar and perirectal skin, prevention is difficult. Also, Gardasil, the HPV vaccination that can prevent transmission, is indicated only for girls and women between 9 and 26. A study on men between 16 and 26 is under way. So for the moment, we have lots of questions but not enough answers. Bowers is board-certified in family practice and is a senior partner with Pacific Oaks Medical Group, one of the largest U.S. practices devoted to HIV care.