Preferentially Expressed Antigen in Melanoma Immunostaining in a Series of Melanocytic Neoplasms

In their 2018 article, Lezcano et al [AJSP 2018(11):1456] show that diffuse tumor cell nuclear reactivity for Preferentially expressed Antigen in Melanoma (PRAME) is a feature of melanoma and that benign and atypical melanocytic tumors are PRAME negative or show only focal positivity for PRAME. We report our observations of PRAME staining in 253 melanocytic tumors. Tumors were classified by hematoxylin and eosin sections. The nuclear PRAME staining of neoplastic melanocytes in each case was categorized as absent, focally present, or diffusely present. The results were compared with those of Lezcano et al 105 of 134 (78%) melanocytic nevi were completely PRAME negative. Of the 29 PRAME-positive benign lesions, 28 exhibited focal but not diffuse positivity, including atypical (n = 11) and dysplastic nevi (n = 11). One of 11 Spitz nevi showed diffuse positivity (9%). Thirty-nine of 51 (76%) invasive melanomas, 41 of 50 (82%) melanoma in situ, and 15 of 18 (83%) metastatic melanomas were diffusely PRAME positive. Excluding desmoplastic melanomas, 39 of 49 (80%) primary melanomas were diffusely PRAME positive. Our findings of PRAME staining in melanocytic neoplasia are in general agreement with those of Lezcano et al. Diffuse PRAME reactivity in neoplastic melanocytes is a feature of malignancy and was only otherwise seen in 1 Spitz nevus. Caution is advised in interpretation of PRAME reactivity in melanocytic tumors of uncertain classification because melanoma arising in association with nevus and some atypical melanocytic tumors may show focal or incomplete PRAME staining. Routine histopathological findings, clinical information, PRAME staining, and judicious application of molecular studies are steps leading to accurate classification of melanocytic neoplasia.