LAUSR

Histologic differentiation of melanoma in situ (MIS) from solar keratosis on chronically sun‐damaged skin is challenging. The first‐line immunostain is usually MART‐1/Melan‐A, which can exaggerate the epidermal melanocytes, causing a diagnostic pitfall for MIS. By comparing MART‐1 and SOX10 immunostaining, we scored the percentage of epidermal melanocytes per 2‐mm diameter fields in pigmented actinic keratosis (n = 16), lichenoid keratosis (n = 7), junctional melanocytic nevus (n = 6), keratosis with atypical melanocytic proliferation (n = 17) and MIS (n = 10). These cases represented an older population (68 years median age) and the head and neck (50%) was the most common anatomic site. MART‐1 score was significantly higher than SOX10 (P value <.05) in solar keratoses, but showed no difference in detecting melanocytic proliferations, demonstrating their equal detection rate of melanocytes. The sensitivity of both MART‐1 and SOX10 was 100%, while their specificities were 17% and 96%, respectively. These results show that SOX10 is more specific than MART‐1 in distinguishing epidermal melanocytes on sun‐damaged skin by avoiding overdiagnosis of melanoma.