The utility of PRAME immunohistochemistry in the diagnosis of melanocytic lesions

Abstract

Preferentially expressed antigen in melanoma (PRAME) is a novel immunohistochemistry (IHC) marker whose principal utility lies in assisting differentiation between melanomas and benign melanocytic proliferations. In most cases, histopathologists can distinguish between naevi and melanoma with ease by using well-established morphologic features however, a definitive diagnosis may be difficult in a subset of cases. PRAME is a cancer testis antigen (CTA) which is normally expressed in the testis, ovaries, adrenal glands and endometrial glands. One hundred and one formalin-fixed, paraffin-embedded (FFPE) sections were tested for PRAME immunohistochemistry (IHC) using primary antibody clone EPR20330. Both the Haematoxylin and Eosin-stained slides and the IHC slides were evaluated with a histopathologist to confirm the diagnosis and determine the PRAME staining score. Most melanomas (83.9%) stained for PRAME while benign melanocytic lesions were generally negative. When a 4+ cut-off was used, PRAME sensitivity was 58.07% while the specificity was 100% with sensitivity increasing to 70.97% and specificity only marginally dropping to 96% with a 3+ cut off. Statistics showed that PRAME can serve as a diagnostic aid to categorise between borderline melanocytic proliferations. It was noted that PRAME does not stain all melanoma subtypes to the same degree. For instance, in this study all ocular melanomas and one metastatic melanoma were negative for PRAME. Nevertheless, PRAME can serve as an additional supportive test for melanoma diagnosis, but should not replace histomorphological evaluation.