McBride JD, McAfee JL, Piliang M, et al. - Findings demonstrate high sensitivity and specificity of 4+ PRAME (preferentially expressed antigen in melanoma) expression in the setting of acral melanomas as well as its superior predictive ability as a diagnostic tool than p16 immunohistochemistry.

• This study included 30 acral melanocytic neoplasms (n = 11 nevi; n = 2 dysplastic nevi; n = 7 Spitz nevi; n = 10 acral melanomas) in which PRAME and p16 expression were assessed.

• PRAME was scored as % positive nuclei: negative = 0%; 1% to 25% = 1+; 25% to 50% = 2+; 50% to 75% = 3+, or positive: 75% to 100% = 4+.

• p16 expression was described as retained (homogeneous or checkerboard) or lost (complete or partial/regionally).

• In all benign, dysplastic, and Spitz nevi, PRAME expression was negative, and all acral melanomas were found to be diffusely (4+) positive for PRAME expression.

• All benign acral nevi exhibited a retained p16 expression, while completely lost and retained expression was seen in one dysplastic nevus and in all acral Spitz nevi, respectively.

• Five of 10 acral melanomas showed retained p16 (3/10 homogeneous; 2/10 checkerboard), and p16 was negative in five of 10 acral melanomas (absent in 3/10, partially lost in 2/10).