No information is available on the clinical use of avelumab during breastfeeding. Because avelumab is a large protein molecule with a molecular weight of about 147,000 Da, the amount in milk is likely to be very low and absorption is unlikely because it is probably destroyed in the infant's gastrointestinal tract. Until more data become available, avelumab should be used with caution during breastfeeding, especially while nursing a newborn or preterm infant. The manufacturer recommends that mothers not breastfeed during treatment and for at least one month after the last dose of avelumab.