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

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.