Breast cancer is the second most common form of cancer diagnosed during pregnancy. The diagnosis and treatment of breast cancer during pregnancy requires multidisciplinary efforts to treat the cancer while protecting the foetus. Pregnancy-related changes in the breast make the diagnosis particularly challenging. Surgery is possible during all three trimesters. Chemotherapy can be administered in the second and third trimesters without increased risk of foetal malformations. Radiation, endocrine and biological therapies however, must be postponed until after delivery.