Most sources consider breastfeeding to be contraindicated during maternal antineoplastic drug therapy, especially alkylating agents such as ifosfamide.[1] Labeling suggests that mothers should not breastfeed during therapy and for 1 week after the last dose of ifosfamide or mesna. Chemotherapy may adversely affect the normal microbiome and chemical makeup of breastmilk.[2] Women who receive chemotherapy during pregnancy are more likely to have difficulty nursing their infant.[1]