Abstract

Hemosiderotic fibrolipomatous tumor (HFLT) is a rare, locally aggressive soft tissue tumor composed of adipocytes, hemosiderin-laden fibroblastic spindle cells, and hemosiderin-laden macrophages with 85% of cases demonstrating a t(1;10)(p22;q24) involving TGFBR3 and/or OGA. HFLT typically presents as a slow-growing subcutaneous mass on the dorsum of the distal extremities, usually the ankle or foot. We describe a case of HFLT with a prominent myxoid stroma. A 62-year-old man presented with a 4-year history of a painless slow-growing mass on his right foot. Examination revealed a 7 cm soft, fixed mass on the dorsomedial aspect of the right foot. MRI showed a multilobulated ill-defined subcutaneous mass with varying degrees of enhancement. An incisional biopsy demonstrated mature adipose tissue admixed with hemosiderin-laden spindle cells arranged in fascicles, myxoid stroma, and patchy chronic inflammation with foamy histiocytes. The spindle cells showed bland nuclei with few intranuclear pseudoinclusions. Cytologic atypia, necrosis, and mitotic activity were absent. The spindle cells were positive for CD34 and negative for calponin, desmin, SMA, S100, HMB45, and SOX10. Iron stain confirmed the hemosiderin. A diagnosis of HFLT was favored on the biopsy and the lesion was excised. Grossly the excision was an 8 cm yellow-orange mass with focally gelatinous cut surfaces. Histologically, the tumor was unencapsulated with no vascular or neural invasion and with features similar to the biopsy, confirming the diagnosis of HFLT. HFLT can pose as a diagnostic pitfall as it can be confused with more common entities including reactive changes, adipocytic tumors including spindle cell lipoma and atypical lipomatous tumor, and fibroblastic tumors such as myxoinflammatory fibroblastic sarcoma, low-grade myxofibrosarcoma, myxoid dermatofibrosarcoma protuberans and superficial acral fibromyxoma.

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