SAN FRANCISCO — A look at the epidemiology of anal cancer demonstrates the need for thorough anal exams, particularly in individuals of both sexes with HIV disease, Joel M. Palefsky, M.D., said at a meeting on HIV management sponsored by the University of California, San Francisco.
Prior to the HIV epidemic, reported rates of anal cancer among men who have sex with men (MSM) were as high as 35/100,000, about the same as the rate of cervical cancer among women before universal screening.
Now, data suggest that MSM with HIV disease have anal cancer rates as high as 100/100,000, or about 10 times the rate of cervical cancer among screened women, which has declined to about 8/100,000, said Dr. Palefsky of the university.
Visual inspection of the anal opening is not sufficient, he said, although this step should certainly not be dispensed with. Visual inspection can, for example, turn up the diffuse, hyperpigmented, flat plaques of Bowen's disease. “Most of the action is occurring intraanally, where you need special techniques to see what's going on.”
Two centimeters inside the anal canal is a transformation zone where the rectal columnar epithelium meets the anal squamous epithelium. This transformation zone is quite similar to the cervical transformation zone, and similarly, that's where most disease occurs.
Anal and cervical disease have many other similarities as well, especially in their association with human papilloma virus (HPV) infection.
After visual inspection, the next step is an anal Pap smear, which must be done without lubricant. Moisten a Dacron (not cotton) swab with tap water or saline and insert it past the anal-rectal junction as far as it will go. As it's pulled out, it will capture a good sample of cells from the transformation zone, which can then be examined cytologically and tested for HPV. Virtually everyone with HIV disease—regardless of gender—will have HPV infection, some with as many as 10 virus types.
A Pap smear tests for dysplasia, not cancer, so the next step is a digital rectal exam, which is a good cancer-screening tool, Dr. Palefsky said. Put a lubricated finger in the anal canal and feel for subcutaneous masses that would not otherwise be visible.
Next, perform an anoscopy with a standard plastic anoscope. Cancerous and precancerous lesions in the anus appear quite similar to what one would see in the cervix.
Dr. Palefsky cautioned against dismissing standard-seeming warts, especially in individuals with HIV disease. These patients often have high-grade disease mixed in with these warts. “We recommend sampling, through biopsy, lesions of different appearance when patients have multiple lesions, which is often the case.”