A novel MAP3K7CL ‐ ERG fusion in a molecularly confirmed case of dermatofibrosarcoma protuberans with fibrosarcomatous transformation

Dermatofibrosarcoma protuberans (DFSP) is a translocation‐associated, low‐grade sarcoma with fibroblastic differentiation. It is the most common superficial sarcoma, almost exclusively arising within the dermis. In a minority of cases, there is a transition from the conventional morphology to a fibrosarcomatous pattern, known as a fibrosarcomatous DFSP (FS‐DFSP). Although a number of different molecular alterations have been described to account for this transformation, it remains poorly understood. Herein we report the first case of a FS‐DFSP with a fusion between ERG, an ETS family transcription factor, and MAP3K7CL , a kinase gene rarely observed in fusion gene events.