Rare Lower Extremity Fibrosarcomatous Variant of Dermatofibrosarcoma With Myxoid Features Treated With Transtibial Amputation.

Dermatofibrosarcoma protuberans (DFSP) is an uncommon soft tissue tumor originating from the dermis, with high rates of local recurrence and invasive growth but low likelihood of distant metastasis. Fibrosarcomatous transformation (FS-DFSP) of DFSP accounts for approximately 5-15% of DFSP tumors, is a higher-grade tumor, with higher chances of metastasis and poorer prognosis. We present a case of a 66-year-old female presented with a large fungating mass on the left dorsal foot. Ultrasound-guided core needle biopsy with immunohistochemistry suggested a spindle cell neoplasm, favoring myxofibrosarcoma with intermediate grade. The patient elected for below-knee amputation over limb salvage with wide resection and free flap reconstruction. Based on clinical presentation, radiologic, histologic features and fluorescence in situ hybridization (FISH) studies confirmed the diagnosis of fibrosarcomatous variant of dermatofibrosarcoma protuberans with myxoid change. FS-DFSP with myxoid change is a rare soft tissue tumor that requires aggressive treatment due to its high rates of recurrence. This case presents a rare tumor in a unique location that was successfully treated with limb amputation, which is not documented in current literature.