A comprehensive survey of driver mutations in mBC demonstrated that the most frequent mutations associated with endocrine therapy-failure were found not only in ESR1 but also in ERBB2 and NF1 when comparing metastases with primary tumours; they found that ESR1 and ERBB2, NF1 mutations (that activate MAPKinase signalling) were mutually exclusive. The gene discussed is ERBB2; the disease is neoplasm.