PRAME immunohistochemistry distinguishes nodal nevi from metastatic melanoma

Background Preferentially expressed antigen in melanoma (PRAME) is a promising immunohistochemical marker for distinguishing benign from malignant melanocytic lesions in lymph node deposits. Objective To evaluate PRAME expression in metastatic melanomas and nevi found in the sentinel lymph nodes of patients with primary melanoma. Methods Thirty patients, comprising 15 nodal nevi and 15 metastatic melanomas, were immunohistochemically analyzed for PRAME expression. Nuclear expression was scored as 0-25%, > 25-50%, > 50-75% or > 75% in tumor cells. The sensitivity, specificity, and positive and negative predictive values were calculated considering nuclear expression of PRAME > 75% as positive cases. Results Cases previously diagnosed as nodal nevi were uniformly negative for PRAME. Conversely, all cases diagnosed as melanoma showed PRAME expression in more than 50% of the cells. Twelve cases showed expression above 75% of cells and were considered positive for calculations, resulting in sensitivity and specificity rates of 80% and 100%, respectively, with corresponding positive and negative predictive values of 100% and 83%. Conclusions A high level of PRAME immunoreactivity was identified in metastatic melanoma, suggesting that PRAME is a useful analytical tool for confirming the diagnosis of melanoma in a melanocytic nodal deposit. Keywords: PRAME, Immunohistochemistry, Metastatic melanoma, Melanocytic nevi, Sentinel lymph nodes