PRAME expression in 137 primary cutaneous melanomas and comparison with 38 related metastases

Melanocytic lesions have always represented a diagnostic challenge for surgical pathologists. According to the literature, PRAME showed great promise as an immunohistochemical tool in the distinction between benign and malignant melanocytic lesions. In the present study, we retrospectively analyzed 137 thicker (Breslow > 1 mm) primary cutaneous melanomas with the aim to better understand the utility of PRAME immunohistochemistry in daily practice and also to investigate if PRAME could represent a prognostic biomarker for cutaneous melanomas. PRAME immunohistochemistry was performed in all melanomas and in the metastases with antibodies to PRAME (dilution 1:1000, clone Ab219650) on an automated immunostainer (Ventana Benchmark Ultra) using a brown chromogen (DAB). We found that melanomas (59.1%) show diffuse PRAME expression (score 4 +). 99 (72.3%) primary cutaneous melanoma had no relapse during the follow-up. Of this group of melanomas, 61/99 (61.6%) were diffusely positive for PRAME. 38 (27.7%) primary cutaneous melanoma had relapses. Of this group, 28/36 (77.7%) were diffusely positive. We did not find any statistical correlation between diffuse PRAME expression and the presence of driver mutation in BRAF gene (p = 0.927), NRAS gene (p = 0.496) or either of the two (p = 0.138). We did not find a prognostic significance of diffuse PRAME expression for relapse (p = 0.462) or survival rate (p = 0.245). The prognostic value of PRAME has been only reported in mucosal, uveal and cutaneous thin melanomas. Here, we show statistical analyses on PRAME expression for melanoma with Breslow > 1 mm based on survival rate and long-term follow-up. According to our results, PRAME is a useful immunohistochemical ancillary tool in daily practice diagnosis of melanocytic lesions.