Melanocytic proliferations associated with lichen sclerosus.

OBJECTIVES To describe the clinicopathologic features of melanocytic proliferations associated with lichen sclerosus (LS) and to compare these findings with those in controls. DESIGN Cohort study. SETTING Academic and private practice dermatology and dermatopathology services. PATIENTS Cases of melanocytic proliferations associated with LS and consecutive controls with persistent (recurrent) melanocytic nevi, persistent malignant melanomas, and compound melanocytic nevi. MAIN OUTCOME MEASURES Diagnostic criteria and disease recurrence. RESULTS Eleven patients, all female, with a mean age of 40 years (range, 8-83 years), presented with pigmented lesions clinically suspected to be malignant melanoma or atypical melanocytic nevi affecting the vulva (7 patients), perineum (3 patients), or chest (1 patient). Lichen sclerosus was first identified in the biopsy specimen and subsequently confirmed clinically. In 10 cases, a melanocytic nevus was superimposed on LS (overlying or entrapped by sclerosis), whereas LS was found at the periphery of vulvar malignant melanoma. After complete excision, no recurrences have been reported for the melanocytic nevi in LS (mean follow-up, 29 months; range, 4-60 months). Compared with control lesions, the LS melanocytic nevi most closely resembled persistent melanocytic nevi and could be distinguished from persistent malignant melanoma histologically. Melanocytes, nevoid or malignant, proliferating contiguously with fibrotic or sclerotic collagen, contained abundant melanin, diffusely expressed HMB-45, and had a higher Ki-67 labeling index than ordinary melanocytic nevi. However, persistent malignant melanoma exhibited mitotic figures, significantly higher Ki-67 labeling index, and deep dermal HMB-45 expression compared with LS melanocytic nevi and persistent melanocytic nevi. CONCLUSIONS Melanocytic nevi occurring in LS have features in common with persistent melanocytic nevi and can mimic malignant melanoma. An "activated" melanocytic phenotype is seen in LS melanocytic nevi, implicating a stromal-induced change.