Cytology in Anal Cancer Screening: Practical Review for Clinicians

The incidence and mortality of anal squamous cell carcinoma (SCC) are expected to continue to increase in the next 20 years. High-risk groups for anal SCC, i.e., human immunodeficiency virus (HIV)-positive patients, men who have sex with men (MSM), women with previous genital neoplasia, and solid-organ transplant recipients, have been identified. HIV-positive MSM have the highest risk, and some societies have advocated for anal cancer screening to be done in this population. Screening for anal SCC follows the same principles as that for cervical cancer since there are similarities between the two types of cancers. Anal cytology has been recommended as an initial screening method for high-risk groups, e.g., HIV-positive MSM. Normally, the cytology is liquid based and collected blindly by a clinician using a Dacron swab and it is especially used for internal lesions detection. The sensitivity to predict anal high-grade squamous intraepithelial lesions is higher in immunosuppressed patients with a high burden of the disease. The report should include the classification, normally according to the Bethesda terminology and the sample adequacy, in a manner similar to that for cervical cytology. In cases involving unsatisfactory samples, it is important to repeat the procedure given the prevalence of anal squamous cytological abnormalities in follow-up cytology procedures. The absence of transformation zone cells in anal cytology seems to increase the risk of false-negative results.