Postoperative radiotherapy and chemotherapy are absolutely contraindicated during pregnancy, even though in the general population mastectomy combined with postoperative radiotherapy has the same prognosis as mastectomy, and for pregnant breast cancer patients, mastectomy is preferred because of the adverse effects of radiotherapy on fetal development. Current studies confirm that the dose of drugs injected during the surgical procedure for biopsy of the anterior lymph nodes has no effect on fetal development. Adjuvant chemotherapy after surgery is contraindicated in the first 3 months of pregnancy because of its teratogenic effects during the fetal organogenesis period. However, there is no evidence for chemotherapy after 3 months.