Multimodality imaging features of primary mammary angiosarcoma: a case report with delayed osseous metastases.

Primary angiosarcoma of the breast is an uncommon and aggressive vascular malignancy that typically affects young women and poses diagnostic and therapeutic challenges. We report the case of a 26-year-old nulliparous woman who presented with progressive left breast swelling over approximately 18 months. Clinical examination revealed diffuse tender swelling without skin discoloration, nipple changes, or palpable lymphadenopathy. Ultrasonography demonstrated a complex cystic mass with thick septations and increased vascularity, while mammography showed global asymmetry of the left breast without suspicious calcifications. Breast MRI revealed a large 8.4 cm heterogeneously enhancing mass in the upper outer quadrant with possible focal skin involvement, but no chest wall invasion or nodal disease. Initial staging with 18F-FDG PET/CT showed no distant metastases. The patient underwent left nipple-sparing mastectomy, and histopathological examination confirmed intermediate-grade primary mammary angiosarcoma, FNCLCC grade 2. Subsequent re-excision achieved clear surgical margins. She received adjuvant ifosfamide-epirubicin chemotherapy and radiotherapy. Initial follow-up imaging showed no residual or recurrent disease. However, 14 months after completion of treatment, follow-up 18F-FDG PET/CT demonstrated new FDG-avid lytic lesions in the sacral and iliac bones, and Breast MRI revealed a small enhancing sternal lesion, consistent with delayed osseous metastatic disease. The patient was treated with palliative radiotherapy and systemic therapy. This case highlights the diagnostic complexity of primary breast angiosarcoma, its potential for delayed hematogenous osseous spread, and the value of multimodality imaging in diagnosis, staging, treatment planning, and surveillance.