Primary Breast Angiosarcoma
Grade I (low) angiosarcomas of the breast have well-defined, irregularly-shaped, anastomosing vascular channels lined by minimally atypical flattened endothelium. The vascular channels are variably dilated or have compressed slit-like lumina. They diffusely infiltrate within the breast parenchyma and fat and surround the terminal duct lobular units (as seen here). The diagnosis of malignancy is rendered on the basis of infiltrative growth pattern. Nuclear atypia is minimal, mitotic activity is low, and papillary endothelial growth is not a prominent feature.