A biologic subset of breast carcinoma defined by high expression of genes characteristic of basal epithelial cells, including KRT5 and KRT17, annexin 8, CX3CL1, and TRIM29, and usually by lack of expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). It is the most common subtype of breast cancer associated with BRCA1 mutations, and is associated with a poor prognosis.