No information is available on the clinical use of osimertinib during breastfeeding. Because osimertinib is 95% bound to plasma proteins, the amount in milk is likely to be low. However, its half-life is about 48 hours and it might accumulate in the infant. The drug also has 2 active metabolites that have not been studied in breastmilk. The manufacturer recommends that breastfeeding be discontinued during osimertinib therapy and for 2 weeks after the final dose.