Evaluating the Diagnostic Utility of PRAME and CD34 Dual Staining in Fibrosarcomatous Dermatofibrosarcoma Protuberans

Abstract Preferentially expressed Antigen in Melanoma (PRAME) is a melanoma-associated antigen that has shown its utility in distinguishing melanoma from benign melanocytic nevi. However, it is reported to express in various other malignancies. Fibrosarcomatous dermatofibrosarcoma protuberans (FS-DFSP) is a high-grade variant of conventional dermatofibrosarcoma protuberans (C-DFSP), characterized by increased cellularity, mitotic activity, and nuclear atypia, with a higher risk of metastasis. Distinguishing FS-DFSP from C-DFSP can be challenging, particularly in cases with ambiguous morphological features. Immunohistochemically, most cases of C-DFSP show diffuse and strong cytoplasmic expression of CD34. Nonetheless, there may be diminished or absent CD34 expressions in FS-DFSP. We present a case of a 49-year-old man with FS-DFSP confirmed by COL1A1:PDGFB fusion, demonstrating a loss of CD34 and positive PRAME expression. This case signifies the potential utility of the CD34-PRAME dual-marker approach in diagnosing FS-DFSP, particularly in morphologically challenging cases. PRAME-positive cases of FS-DFSP can also be considered as a potential therapeutic target with PRAME-specific immunotherapy.