Breast cancer during pregnancy and lactation refers to breast cancer that occurs during pregnancy and one year after delivery. Being a beautiful mother is the beautiful wish of every woman, but the incidence of breast cancer is getting younger and younger. Therefore, breast health during pregnancy and lactation should not be ignored. Breast cancer during pregnancy and lactation usually presents with painless lumps in the breast, bloody nipple overflow, or even enlarged axillary lymph nodes. On the one hand, during pregnancy and lactation, the hormone secretion in women’s body is high, and the level of sex hormone is much higher than usual, which prompts the cancer cells to proliferate and develop more rapidly; on the other hand, the physiological enlargement of breast under the effect of progesterone and prolactin during pregnancy and lactation often makes the cancer lump not easy to be detected or misdiagnosed as breast cancer. On the other hand, the physiological hyperplasia and enlargement of breast during pregnancy and lactation under the effect of progesterone and prolactin often make the cancerous masses not easy to be detected or misdiagnosed as inflammatory breast masses or benign tumors and delay treatment. Because breast cancer cells proliferate rapidly during pregnancy and lactation, the cancer is not easy to be detected, and women are often in good condition because of the increase of hormone level in their body. Breast cancer is a systemic and systemic disease, and all treatments for breast cancer may affect the fertility of patients. Does breast cancer treatment during pregnancy affect the mother and fetus? Should breast cancer patients terminate their pregnancy or not? Fertility or survival is a difficult question. The treatment of breast cancer during pregnancy and lactation is the same as the general principles of breast cancer management, the special thing is how to deal with the relationship between anti-cancer treatment and pregnancy and lactation. The general principles are: (1) For breast cancer patients in the first trimester of pregnancy, NCCN guidelines recommend that patients need to consider stopping pregnancy. If the patient insists on continuing the pregnancy, mastectomy and axillary lymph node dissection will be required. Then, adjuvant chemotherapy is administered as the pregnancy enters the middle trimester. After delivery, radiation therapy and endocrine therapy are then administered. (2) If breast cancer is detected in the middle 3 months of pregnancy or in the last 3 months of pregnancy, mastectomy or breast-conserving surgery with lymph node dissection should be performed, and chemotherapy can be administered immediately after surgery. If breast-conserving surgery is chosen, radiotherapy and endocrine therapy will need to be considered after delivery. In order to avoid the problem of anticancer drugs causing malformation to the fetus, it is better to wait for more than 2 years after the complete cessation of anticancer treatment if you want to have another baby after breast cancer treatment. Breast cancer during breastfeeding: Once the diagnosis of breast cancer is established, breastfeeding should be stopped immediately. It is contraindicated to use female hormone or mannitol hot compress when breastfeeding back in order to prevent cancer cells from metastasis and spreading. Chinese herbal medicine: 60g of raw malt and 60g of fried malt can be used to make tea and drink it frequently, which can generally achieve the effect of returning breast milk within 1 week. After breast regression, you can receive breast cancer treatment. Individual patients can receive pre-surgical chemotherapy during the breast recovery period. The joy of being a first time mother is indescribable, but if this beautiful dream has to be aborted due to an unexpected breast tumor, what a shock to life! We remind young mothers-to-be who are planning to have a pregnancy to have a breast health check-up 6 months before pregnancy, and to go to a specialized hospital as soon as possible if you find any abnormalities in the breast during pregnancy and breastfeeding.