Cellular Dermatofibroma Harboring a Novel MYADM::PRKCG Gene Fusion: A Case Report

Abstract: The application of molecular techniques has significantly refined the classification of cutaneous mesenchymal tumors, uncovering recurrent genetic alterations that aid in diagnostically challenging cases. Dermatofibroma, or cutaneous fibrous histiocytoma, is a common benign neoplasm with broad morphologic variability and limited immunohistochemical specificity, for which recurrent protein kinase C gene fusions have recently been described. We report a novel case of a cellular, pseudoangiomatous DF arising on the dorsum of a 56-year-old man and harboring an in-frame MYADM::PRKCG fusion transcript. Histologically, the lesion displayed high cellularity and prominent vascularity, and focal smooth muscle actin and desmin positivity, initially suggesting angiomatoid fibrous histiocytoma. Targeted RNA sequencing identified a previously unreported MYADM::PRKCG fusion, enabling definitive classification. This is the first description of a MYADM::PRKCG rearrangement in DF, further expanding our knowledge about the molecular landscape of this neoplasm.