Six months after a road traffic accident in which she sustained blunt chest trauma, a 45-year-old woman has a 3 cm firm breast lump with overlying skin retraction. Biopsy shows an ill-defined area of necrotic fat, lipid-laden macrophages, foreign body giant cells and haemosiderin deposits, surrounded by fibrosis. No epithelial cells are seen. The most likely diagnosis is:

• A Fat necrosis ✓
• B Invasive ductal carcinoma with desmoplasia
• C Diabetic mastopathy
• D Granular cell tumour

Explanation

Fat necrosis follows trauma, surgery or radiation and produces a firm lump with skin tethering that clinically mimics carcinoma. The biopsy shows necrotic adipocytes, foamy histiocytes, multinucleate giant cells and haemosiderin with eventual fibrosis and dystrophic calcification. The absence of any epithelial atypia excludes invasive ductal carcinoma, the main mimic. Diabetic mastopathy features dense keloid-like stromal fibrosis and lobular lymphocytic infiltrates in long-standing diabetics, and granular cell tumour shows S100 positive polygonal cells.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.