Clinicopathological classification of breast cancers using immunohistochemistry distinguishes the ER+ and HER2+ subtypes and places those tumors that cannot be defined further into a group that has become known as triple-negative breast cancer (TNBC), based on a low level of immunohistochemical signal for ER, PR, and HER2. The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.