High resolution anoscopy (HRA)—whereby a provider uses a plastic anoscope, a small camera, tissue staining solutions and tissue biopsy—is the most cost-effective way to screen for anal cancer, despite being one of the most expensive methods. This finding was published online December 6 in the journal AIDS.

Rates of anal cancer are as much as 160 times higher in HIV-positive men who have sex with men (MSM) than the general public. For this reason, many experts recommend annual screening. Unfortunately, no study has yet determined which of several available methods is most cost effective for this purpose.

HRA is considered the gold standard for the detection of cells that are progressing toward anal cancer. It has the highest sensitivity—meaning that it is most effective at finding precancerous lesions—and the highest specificity—meaning that it can distinguish between the most serious lesions (called anal intraepithelial neoplasia grades 2 or 3 [AIN 2/3]) and the less dangerous lesions.

Aside from HRA, the two other methods for anal cancer screening are a genetic test used to detect the presence of cancer-causing strains of human papillomavirus (HPV)—a virus known to cause anal and cervical cancer—and swabs of anal tissue (Pap smears) followed by cell analysis. Neither of these two methods is as effective at detecting precancerous lesions as HRA, but both are much cheaper than HRA and don’t require significant training of providers. For this reason, some experts have previously proposed that the most cost-effective way to screen for anal cancer would be to use one or both of these cheaper tests first.

To determine which of a variety of combinations of the three screening tools was most cost-effective, Jonathon Lam, PhD, from the University of Toronto, and his colleagues used data from a Canadian anal cancer study that had 401 HIV-positive MSM. Cost effectiveness was determined by three factors: the actual cost of the test, the sensitivity of the tests, and the specificity of the tests.

In the anal cancer study, HRA results were available for all 401 men, of whom 98 (24 percent) had AIN 2/3. Lam’s team then used data from previous studies on the sensitivity and specificity of HPV testing and Pap smears to calculate which combinations of the three methods would be able to detect the most AIN 2/3 cases effectively at the lowest annual cost.

A variety of treatment algorithms were tested. For example, one algorithm had people proceed directly to HRA. Another had people proceed to HRA if they had an HPV test result that indicated they carried the cancer-causing strains. Another had people proceed from a positive HPV test to a Pap test, and then on to an HRA only if the Pap test detected some degree of cell abnormality.

Lam and his colleagues found that HRA was by far the most cost-effective method of detecting AIN 2/3. Most other combinations missed cases of AIN 2/3, which means that the lesions could have progressed to anal cancer, leading to much more costly treatment and greater suffering, illness and possibly death. Even when a certain screening algorithm ultimately detected AIN 2/3, the combination of the tests and the frequency of their use—before proceeding to HRA—meant that it would have been far cheaper if HRA were used in the first place to screen for the lesions.

“In summary, for HIV-infected MSM and where resources permit, anal cancer screening should be initiated with the direct use of HRA since this is the most cost-effective strategy for detecting AIN 2/3,” the authors conclude.