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.

The PD-1/PD-L1 pathway plays a critical role in the physiologic inhibition and modulation of the immune response in normal tissue. Many tumors evade immune detection and response by upregulating PD-L1 expression. Humanized monoclonal PD-1 and PD-L1 antibodies have proven as both tolerable and effective treatment in many neoplasms. Extramammary Paget disease (EMPD) is a deformative and debilitating cutaneous malignancy in which definitive treatment options are limited with high recurrence rates after surgical excision. To the best of our knowledge, there is little published information regarding EMPD and PD-L1 expression. We evaluated 18 EMPD surgical pathology cases for tumor cell and tumor-associated inflammatory (TAI) cell PD-L1 expression. We identified PD-L1 tumor cell expression in 3 (17%) of the cases: 2 of 4 invasive cases (50%) and 1 of 14 (7%) noninvasive cases. One invasive case had lymph nodal metastasis with PD-L1 tumor cell expression. The host inflammatory response intensity and PD-L1 expression were variable in cases negative for tumor cell PD-L1 expression; however, a marked inflammatory response and TAI PD-L1 expression were present in all cases positive for tumor cell PD-L1 expression. In conclusion, 1 in 14 (7%) in situ EMPD cases showed tumor cell PD-L1 expression and 2 of 4 invasive cases (50%) showed tumor cell PD-L1 expression. TAI cells were more often positive (83%) than tumor cells (17%) for PD-L1 expression.

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