ERBB4 and neoplasm: ERBB3 mutations were identified in 1/40 (2.5%) HER2 negative tumours and 1/29 (3.4%) of HER2-positive tumours, while mutations in ERBB4 were identified in 2/40 (5%) HER2-negative tumours and 2/29 (6.9%) HER2-positive tumours.