PRAME immunohistochemical expression in recurrent/traumatized melanocytic nevi and the pitfall of expression by reactive fibroblasts

Introduction: The recurrent/traumatized melanocytic nevus (RTMN) refers to melanocytic lesions that reappear following incomplete removal or trauma to a previous nevus, often presenting clinically and dermoscopically similar to melanoma, which complicates differential diagnosis. Histologically, RTMN exhibit melanocytic proliferation and scar tissue from prior trauma or excision. PRAME (pref-erentially expressed antigen in melanoma) immunohistochemistry (IHC) is emerging as a diagnostic tool for distinguishing between nevi, melanoma, and nevus-associated melanomas. However, its role in RTMN has not yet been established. Objectives: This study aimed to evaluate the expression of PRAME in RTMN, specifically in the melanocytic and fibroblastic components, to explore its potential diagnostic utility. Methods: A series of 22 RTMN cases from the Pathology Unit of the University of Campania Luigi Vanvitelli Hospital were reviewed. PRAME IHC was performed on formalin-fixed, paraffin-embedded tissue, and staining was evaluated in three compartments: junctional melanocytic, intradermal melanocytic, and fibroblastic scar tissue. Results: PRAME IHC showed no positivity in the junctional or intradermal melanocytic components of any case. However, five out of 22 cases (22.7%) demonstrated PRAME positivity in the fibroblastic component, which was statistically significant (P=0.0169). Conclusions: This study suggests that PRAME IHC is negative in the melanocytic components of RTMN, distinguishing it from melanoma. However, PRAME positivity in the fibroblastic scar component warrants careful interpretation to avoid diagnostic pitfalls. These findings emphasize the importance of considering the histological context when using PRAME as a diagnostic marker in RTMN.