Abstract

Dedifferentiated and undifferentiated melanomas (DM/UM) pose challenges in terms of tumor diagnosis due to their underrecognized histology and lack of typical immunohistochemical features seen in melanomas. These tumors exhibit a lack of expression of commonly used melanoma markers, but little is known about the expression of the PRAME protein. Herein, we aim to explore the potential utility of PRAME expression in diagnosing these melanomas, which were identified based on previous medical history and clinical information. We examined 11 DM/UM cases from our institutional archives, consisting of 2 UM and 9 DM. PRAME immunohistochemical expression was assessed using a semi-quantitative method, evaluating both intensity and percentage positivity. Our cohort comprised 4 men and 7 women, ranging in age from 44 to 89 (median 76). Among the 11 cases, 6 exhibited focal or patchy positivity for at least one melanocytic marker (SOX10, S100, Melan-A, HMB-45). Following PRAME staining, diffuse nuclear expression was observed in 7 cases (64%). Strong nuclear staining was present in 3 cases (27%), while 1 case (9%) showed no expression. We found no correlation between melanocytic marker positivity and survival outcome. Our findings suggest that PRAME expression could serve as a useful diagnostic tool for suspected dedifferentiated/undifferentiated melanoma, independent of other known melanocytic markers. Further comparative analysis is underway to investigate the specificity of this marker using AFX and PDS as comparators in this context.