B. Hemosiderotic fibrolipomatous tumor
Diagnosis of hemosiderotic fibrolipomatous tumor (HFLT) was confirmed, with pathology results demonstrating mixed fibrous and mature adipose tissue with extensive pigment deposition (Figure 2A). Lesional cells were spindled, ovoid, and epithelioid, with open chromatin, prominent nucleoli, and without mitoses (Figure 2B). A mixed inflammatory infiltrate that included neutrophils, histiocytes, and foamy macrophages was present. Immunohistochemistry results were strongly positive for CD34 (Figure 2C) in the lesional cells but negative for S100, SRY-box transcription factor 10 (SOX10), human melanoma black 45 (HMB45), and Melan-A (not shown).
The HFLT tumor is a rare, slow-growing painful subcutaneous mass characterized by varying proportions of mature adipocytes, spindle cells, and hemosiderin pigment.1 These tumors typically stain positive for CD34 and negative for desmin, smooth muscle actin, keratin, and S100.2 While HFLTs predominantly occur on the foot and ankle, these tumors can also occur elsewhere on the body, including the hand and/or wrist in up to 10% of reported cases.1- 7