Answer: Angiosarcoma

Histology: The tumor is centered in the dermis of the breast. While in some areas it demonstrates well-formed vascular channels, other areas demonstrate solid growth and therefore qualify the tumor as high-grade. Characteristically, these tumor cells feature vesicular chromatin and prominent nucleoli. Mitoses are readily apparent.

Discussion: Metaplastic carcinoma should be centered with the parenchyma of the breast, typically demonstrates a heterogeneous pattern, and does not usually show vascular differentiation. Atypical vascular lesions are small dermal vascular proliferations without significant atypia which arise in patients who have received radiation therapy for breast carcinoma. These lesions are typically circumscribed and are associated with a benign clinical course. Malignant fibrous histiocytoma is a diagnosis reserved for tumors showing fibroblastic differentiation and pleomorphic cytology. These lesions have a storiform pattern and are typically centered in the deep soft tissues.

Angiosarcoma of the skin of the breast is distinguished from other post-radiation angiosarcomas by the fact that its latency period is short. While most radiation-induced sarcomas occur over seven years after radiation therapy, angiosarcoma of the skin of the breast may arise within three years of radiation therapy for breast cancer. In the current case, the patient had an invasive breast carcinoma treated by lumpectomy, and these patients are almost uniformly treated with adjuvant radiation therapy.