Angiosarcoma is a type of cancer that starts from the endothelial cells on the inside of blood vessels. It is a relatively rare form of breast cancer with an incidence of 0.05% of all primary malignancies of the breast. Many cases of angiosarcoma in the breast are associated with prior radiation treatment. Microscopically it is characterized by abnormal anastomosing and dissecting vascular channels that can be highlighted with the markers CD31, CD34, and ERG.