No information is available on the clinical use of mosunetuzumab during breastfeeding. Because mosunetuzumab is a large protein molecule with a molecular weight of 146,000 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] The manufacturer recommends that breastfeeding be discontinued during mosunetuzumab therapy and for 3 months after the last dose.