No information is available on the clinical use of blinatumomab during breastfeeding. Because blinatumomab is a large protein molecule with a molecular weight of about 54,000 Da, the amount in milk is likely to be very low.[1] It is also likely to be partially destroyed in the infant's gastrointestinal tract and absorption by the infant is probably minimal.[2] Waiting for at least 2 weeks postpartum to resume therapy may minimize transfer to the infant.[3] Until more data become available, blinatumomab should be used with caution during breastfeeding, especially while nursing a newborn or preterm infant. The manufacturer recommends that breastfeeding be discontinued during blinatumomab therapy and for at least 48 hours after treatment.