Melanocytes in long-standing sun-exposed skin: quantitative analysis using the MART-1 immunostain

To help distinguish early melanoma from normal sun-damaged skin by quantifying the density, confluence, and depth of follicular penetration of melanocytes in long-standing sun-exposed skin of the face and neck.

Case series.

Referral center.

Random selection of 149 patients undergoing Mohs surgery for basal cell and squamous cell carcinomas of the face and neck.

Frozen-section slides were made from long-standing sun-exposed normal skin and stained with MART-1 (melanoma antigen recognized by T cells 1 staining) immunostain.

The number, confluence, and depth of penetration of melanocytes along the follicular epithelium were quantified per high-power field (original magnification x 400, equivalent to 0.5 mm of skin). Confluence was categorized by the number of adjacent melanocytes (none, 0-1; mild, 2; moderate, 3-6; and severe, >6).

The mean number of melanocytes per high-power field was 15.6 (range, 6-29). Confluence was severe in 1.0% of the specimens, moderate in 34.0%, mild in 54.0%, and absent in 11.0%. Focal areas of increased melanocyte density occurred in 24.2% of the specimens; in these areas, the mean number of melanocytes per high-power field was 20.3 (range, 7-36) and the confluence of melanocytes was severe in 13.0%, moderate in 50.0%, and mild in 37.0%. The mean depth of follicular epithelium penetration by melanocytes was 0.38 mm. Pagetoid spread and nesting of melanocytes were not seen. Nonspecific scattered MART-1-staining dermal cells were in half of the slides.

Melanocytes in long-standing sun-exposed skin have an increased density and a confluence that is often moderate (3-6 adjacent melanocytes), but they do not exhibit pagetoid spread or nesting. Nonspecific MART-1-staining dermal cells should not be interpreted as invasive melanoma.