Original ArticlesImmunohistochemistry for PRAME in the Distinction of Nodal Nevi From Metastatic MelanomaLezcano, Cecilia MD; Pulitzer, Melissa MD; Moy, Andrea P. MD; Hollmann, Travis J. MD, PhD; Jungbluth, Achim A. MD; Busam, Klaus J. MD Author Information Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, NY Conflicts of Interest and Source of Funding: Supported in part by the Cancer Center Support Grant of the National Institutes of Health/National Cancer Institute under award number P30CA008748. The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Correspondence: Cecilia Lezcano, MD, Department of Pathology, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10065 (e-mail: [email protected]). The American Journal of Surgical Pathology 44(4):p 503-508, April 2020. | DOI: 10.1097/PAS.0000000000001393 Buy Metrics Abstract The distinction of metastatic melanoma from melanocytic nevi in lymph nodes can on occasion be difficult. As diffuse immunohistochemical (IHC) PRAME (PReferentially expressed Antigen in MElanoma) expression is detected in the majority of primary and metastatic melanomas, but rarely in nevi, we reasoned that PRAME could be a useful adjunct marker for the diagnosis of melanocytes in lymph nodes. In this study, we examined 45 nodal melanocytic deposits comprising 30 nodal nevi and 15 melanoma metastases. The latter were diagnostically not straightforward because they either coexisted with nodal nevi or were present in perinodal fibrous tissue. All nodal nevi (30/30) were negative for PRAME, whereas all melanoma metastases (15/15) were diffusely positive for PRAME IHC. We additionally report the novel use of a PRAME/Melan A dual-label immunostain. Our results show that PRAME IHC may be useful in the assessment of diagnostically challenging nodal melanocytic deposits, such as intraparenchymal nodal nevi, metastases confined to the capsular fibrous tissue, or in the setting of small metastases coexisting with a nodal nevus in the same lymph node. Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.