Breast cancer is the most commonly occurring form of cancer in pregnancy. Among women aged between 25 and 29 years, one in five cases of breast cancer will occur in pregnancy or during the first postnatal year. The prevalence is increasing, presumably because of the increase in maternal age at pregnancy. Interdisciplinary cooperation is needed to ensure a good outcome for both mother and child. The prognosis is good but depends on rapid diagnosis and optimal treatment. In this clinical review article, the most important aspects of breast cancer treatment during pregnancy are reviewed.