Pregnancy-associated breast cancer accounts for 10–20% of all breast cancers in women under the age of 30 years. The diagnosis and treatment of this type of cancer require an assessment of the risk of different management methods for the embryo or fetus. Computed tomography and positron emission tomography are absolutely contraindicated in pregnancy. Surgical management, i.e. radical mastectomy, which may be performed at any stage of pregnancy, or breast conserving treatment, which is recommended only in the third trimester, is standard treatment. Doxorubicin/anthracycline-based chemotherapy is considered relatively safe in the second and the third trimester. Hormonal treatment, trastuzumab and bisphosphonates are contraindicated. Special restrictions have been introduced for radiation therapy. The consequences of intrauterine exposure to radiation depend on the stage of pregnancy, radiation dose and dose rate. Preimplantation radiation can cause death of the embryo or radiation-induced carcinogenesis. There is a risk of delayed fetal growth and organ malformations in the period of organogenesis. Exposure to radiation between 8 and 25 weeks gestation is associated with the risk of intellectual disability, microcephaly and carcinogenesis. Exposure after 25 weeks gestation is associated only with the risk of carcinogenesis. It was estimated that targeting the chest with therapeutic radiation doses during pregnancy causes unacceptable fetal exposure to radiation. Electron beam intraoperative irradiation of the breast tumor bed is the only acceptable radiation method in the first and the second trimester. The decision on initiation and continuation of cancer therapy in a pregnant patient should be based on a detailed analysis of potential benefits and risks as well as patient’s will.