Digital Atlas of Breast Pathology by Meenakshi Singh, MD © - Department of Pathology, Stony Brook University Medical Center

Metaplastic carcinoma, angiomatoid type. Low power.
Has differentiation towards different non-native breast structures; a vascular form (angiomatoid) is not unexpected. While a large proportion of the malignant cells are solid, there are areas with lumen containing red blood cells, a key feature of this differentiation.