The density and distribution of melanocytes adjacent to melanoma and nonmelanoma skin cancers

Background: The determination of clear margins during Mohs surgery for melanoma in situ arising on sun-damaged skin is often made difficult by the presence of background atypical melanocytic hyperplasia. Objective: To determine the density and distribution patterns of melanocytes adjacent to melanoma and nonmelanoma skin cancers. Methods: 180 skin specimens obtained during the routine repair of defects resulting from the removal of melanoma and nonmelanoma skin cancers were analyzed using H&E-stained permanent sections to determine the quantity and distribution of epidermal melanocytes. Results: The mean melanocyte density was 7.97 melanocytes per 1 mm of epidermis (SD,+/- 6.7). Contiguous melanocytes were found in 30 (16.7%), atypical melanocytes were observed in 8 (4.4%), and follicular extension of melanocytes was observed in 11 (6.1%) of the specimens. These features were significantly associated with higher melanocyte densities (p < .001) and were more commonly observed in specimens from patients with melanoma. Conclusions: There is a high degree of variability in melanocyte densities seen adjacent to melanoma and nonmelanoma skin cancers. Contiguous melanocytes, atypical melanocytes, and follicular melanocytes can be seen in the sun-damaged skin surrounding both melanoma and nonmelanoma skin cancers, but especially with melanoma. Because some of the features of melanoma in situ can be seen in chronically sun-damaged skin, the Mohs surgeon should be cautious when assessing the margins for melanoma in this setting.