Belantamab mafodotin has been discontinued in the United States. No information is available on the clinical use of belantamab mafodotin during breastfeeding. Because belantamab is a large protein molecule with a molecular weight of 152,000 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] However, belantamab is conjugated with the small-molecule toxin, mafodotin, which might be excreted into milk and absorbed by the infant. Because of the potential for serious adverse reactions in the breastfed infant, the manufacturer recommends that breastfeeding be discontinued during therapy and for 3 months after the last dose.