ERBB2 and breast carcinoma: In studies summarizing results of patients exposed to tamoxifen during pregnancy, the rate of major malformations after tamoxifen exposure was 17.6% compared to 3% in the general non-exposed population.46 HER2-targeted agents are contraindicated during pregnancy due to obstetric risk, as trastuzumab has been associated with oligohydramnios and anhydramnios.47 There is a paucity of data regarding other HER2-targeted agents, such as pertuzumab, trastuzumab emtansine (T-DM1), and neratinib, which are increasingly used in the early breast cancer setting.