This chapter describes the diagnosis, surgical intervention, and prognosis for breast cancer in pregnancy. Estrogen receptor-negative and progesterone receptor-negative tumors, which correlate with poor prognoses, are more common among pregnant women than among age-matched controls, possibly due to receptor down-regulation in pregnancy. The rate of mastectomy among pregnant women is higher than the rate of lumpectomy due to large tumor size and avoidance of adjuvant radiation, but breast-conserving surgery is becoming more frequent. Radiation therapy administered either to complete breast-conserving surgery, as postmastectomy adjuvant treatment in high-risk patients or as a palliative treatment for metastatic cancer, is contra-indicated during pregnancy because of fetal exposure. Chemotherapy should be avoided four weeks before the anticipated delivery date to reduce the risk for infection, or hemorrhage due to pancytopenia. Comparisons between pregnant and nonpregnant women of matched age, nodal status, estrogen receptor status, and tumor histopathology and size yielded no differences in prognosis.