A subgroup of melanocytic nevi on the distal lower extremity (ankle) shares features of acral nevi, dysplastic nevi, and melanoma in situ: a potential misdiagnosis of melanoma in situ.

Melanocytic lesions in certain locations (eg, genital, breast, acral) may have histologic and clinical features simulating melanoma. Here we describe a group of lesions from the lower distal extremity and analyze their histologic features and possible relation to dysplastic nevi (DN) and melanomas. One hundred fifteen melanocytic lesions from the ankle were retrieved from January 1990 to August 2006 from the files of M. D. Anderson Cancer Center and were classified as benign melanocytic nevi (BN; n=17), DN (n=35), melanomas (MM; n=52), and melanocytic nevi of the ankle with atypical features (MNAAF; ie, cases that did not readily fit in any of the previous categories, n=11). Data analyzed included clinical (age and sex) and histologic features (circumscription, symmetry, cohesiveness of nests, suprabasal melanocytes, confluence, single-cell proliferation, nuclear chromasia, size, and nucleolar features). Follow-up was collected for all MNAAF. MNAAF differ from the other types of lesions in regard to sex incidence (73% in women). The median age of those patients MNAAF was 47 years (range 29 to 76 y). All MNAAF showed moderate-severe architectural disorder whereas 78% showed only mild-moderate cytologic atypia. No MNAAF cases had recurred after follow-up (4 mo to 13 y). This study highlights a group of melanocytic lesions located on the ankle that share histologic features with acral nevi, DN, and melanoma. These lesions are more predominant in females and have moderate to severe architectural atypia but only mild-moderate cytologic atypia. After complete excision, follow-up data indicate an apparently benign outcome. Pathologists should be aware of this type of lesions to avoid overdiagnosis of melanoma.