ERBB2 and breast cancer: While approximately 3% of all breast cancers in the US are associated with a gBRCAm, pathogenic variants of these genes are prevalent in more than 10% of patients with triple-negative breast cancer (TNBC)—tumors that lack estrogen and progesterone receptors and do not overexpress ERBB2 protein.4,5,6 Triple-negative breast cancer generally has more limited therapeutic options and poorer prognosis than other types of breast cancer.7,8 In the OlympiA trial, more than 80% of patients in both arms had TNBC.