No information is available on the clinical use of calaspargase pegol during breastfeeding. Because calaspargase is a large protein molecule with a molecular weight of about 140,000 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] Polyethylene glycol is not excreted into breastmilk.[3] However, the manufacturer recommends that the drug not be used during breastfeeding and for 3 months after the last dose.