The presence of numerous melanocytic nevi is a significant melanoma risk factor, but there are scant data related to prevalence and morphologic features of melanocytic nevi in the perianal area. The prognosis of perianal melanoma is often dismal because of hidden location and diagnosis delay.

To determine prevalence and morphologic features of perianal melanocytic nevi.

This study was conducted for 11 months during 2013 and 2014 at an outpatient dermatology clinic in Chicago, Illinois, with a convenience sample of 236 adults (men and women of all races, ≥18 years) presenting to 1 dermatologist for melanoma and/or skin cancer screening or surveillance. The analysis was conducted during April through July 2015.

Prevalence and morphologic features of perianal nevi according to race/ethnicity, sex, and age.

Of 236 participating patients, 219 were non-Hispanic white; 4, Hispanic white; and 13, nonwhite. Patients included 138 men and 98 women, ages 23 to 84 years (median age, 55 years; mean [SD], 53 [15] years). Perianal nevi of any size, at least 2 mm in diameter, and at least 5 mm in diameter were evident in 48.9% (107 of 219), 39.7% (87 of 219), and 5.5% (12 of 219) of non-Hispanic whites, respectively; 50.0% (2 of 4), 0 (0 of 4), and 0 (0 of 4) of Hispanic whites, respectively; and 38.5% (5 of 13), 38.5% (5 of 13), and 0 (0 of 13) of nonwhites, respectively. In non-Hispanic whites, the presence of at least 1 perianal nevus was significantly associated with history of atypical nevus excision (odds ratio [OR], 2.9; 95% CI, 1.5-5.7); and extant findings of at least 1 atypical nevus (OR, 2.2; 95% CI, 1.3-3.9); atypical nevus pattern (≥20 nevi that were ≥2 mm in diameter), plus at least 5 nevi that were 5 mm or greater in diameter (OR, 1.8; 95% CI, 1.1-3.1); and at least 4 atypical nevi 5 mm or greater in diameter (OR, 1.9; 95% CI, 1.1-3.3).

In this study, perianal melanocytic nevi were common and were associated with prominent and atypical nevi elsewhere. The perianal area is worthy of attention during melanoma screening and surveillance.