Trastuzumab treatment for breast cancer during pregnancy

QUESTION: One of my patients has been diagnosed with breast cancer and started treatment with trastuzumab. She has recently discovered that she is pregnant and wishes to continue the pregnancy. What are the consequences of trastuzumab treatment during pregnancy and can she continue her pregnancy? ANSWER: Human data regarding the safety of trastuzumab during pregnancy are scarce. Only 3 case reports could be located in the published literature. Anhydramnios was observed in a case where the exposure to trastuzumab occurred during the second trimester, which reversed after discontinuation of the drug without any apparent consequences to the baby. Evidence is insufficient to provide any recommendations, but in light of the case reports, pregnancies exposed to trastuzumab during the second trimester should be closely followed with particular attention to amniotic fluid volume.