Case Report: Chronic expanding axillary hematoma mimicking locoregional recurrence 15 years after breast cancer surgery.

Chronic expanding hematoma (CEH) is a rare condition characterized by progressive enlargement of a hematoma long after an initial hemorrhagic event and may mimic malignancy. We report a 61-year-old woman who developed a progressively enlarging left axillary mass 15 years after modified radical mastectomy followed by adjuvant chemotherapy and radiotherapy for breast cancer. The lesion became ulcerated and spontaneously bled, raising concern for locoregional recurrence. Ultrasonography demonstrated heterogeneous mixed cystic-solid lesions, while systemic evaluation revealed no evidence of distant metastatic disease. Ultrasound-guided core needle biopsy showed hemorrhage, fibrin deposition, and fibrous tissue without malignant cells but was considered inconclusive because of potential sampling limitations. Surgical excision and extensive debridement were therefore performed. The 7 × 5 × 2 cm excised specimen was extensively sampled in 20 tissue blocks and demonstrated organized hematoma, fibrosis, hemosiderin-laden macrophages, and chronic inflammatory changes, without atypical endothelial proliferation or malignant tumor cells. CEH was definitively diagnosed. Following staged wound management with vacuum sealing drainage, the axillary defect was successfully reconstructed using a pedicled scapular artery perforator propeller flap. This case emphasizes the importance of considering CEH, recurrent carcinoma, and angiosarcoma in the differential diagnosis of delayed hemorrhagic masses after breast cancer treatment and highlights the importance of adequate histopathological sampling for definitive diagnosis.