A number of key issues must be considered regarding the treatment of a malignancy in pregnancy. The optimal dosing of chemotherapy during pregnancy is an important issue that requires consideration as the blood volume is 50% higher in pregnant women. The main adverse effect from dose-dense chemotherapy is neutropenia, which in nonpregnant patients is frequently managed by the use of granulocyte colony stimulating factor (G-CSF). Antimetabolites are small, weakly acidic molecules used to treat leukaemia, lymphoma and breast cancer. The concentrations in milk are variable and related to the dose and timing of chemotherapy and all standard advice is that breastfeeding is contraindicated while undergoing chemotherapy. The maternal benefits of receiving chemotherapy before delivery must outweigh the fetal risks of exposure and the maternal risk of delaying treatment until after delivery at a gestational age optimal for both fetal survival and wellbeing.