The chance of breast cancer in breastfeeding women is not very high, but people need to be fully aware of the symptoms of breast cancer during breastfeeding to avoid not being able to judge accurately when the suspected symptoms appear, thus delaying the best time for treatment. The following are some of the symptoms of breast cancer during breastfeeding, we should pay more attention to breast health in general and go to the hospital to find out the specific cause once the suspicious symptoms appear. According to foreign reports, the incidence of breast cancer accounts for about 0.2-0.3% of all pregnant women; 2-3% of all breast cancer patients; domestic reports are higher than foreign levels, accounting for about 7-12% of all breast patients. Generally speaking, primary breast cancer that occurs at the same time of pregnancy or within one year of pregnancy is called gestational breast cancer, while primary breast cancer that occurs during breastfeeding is called lactational breast cancer. This type of breast cancer is less common clinically, but should not be taken lightly. Breast cancer during breastfeeding is mostly seen in women under 35 years old. Due to the change of hormone level in the body, i.e. estrogen and adrenocorticotropic hormone increase significantly, prolactin and growth hormone level increase during lactation, and the decrease of T-cell count in blood, the immune function of the body decreases, resulting in faster growth and higher malignancy of the tumor; meanwhile, due to the increase of capillaries in the breast and expansion of congestion during pregnancy and lactation, the tumor can spread easily. In addition, due to the increase of breast parenchyma and glandular hyperplasia, the physiological enlargement and hardness of breasts make the tumor not easy to be found at an early stage, and once found, most of them are in the middle and late stage. Therefore, we must be alert to breast cancer during lactation. The symptoms of breast cancer during lactation are similar to those of breast cancer in general, mainly lumps and nipple drainage in the breast, which is usually a single duct in one breast. It is often accompanied by enlarged axillary lymph nodes. Due to the enlargement of the breast and the increased density of breast tissue, X-ray examination often does not easily reveal the tumor, which makes early diagnosis difficult. The choice of treatment for breast cancer in pregnancy should be decided according to the early and late stage of the tumor and the different stages of pregnancy. Generally, it is believed that early pregnancy of stage I breast cancer patients can be terminated without termination of pregnancy, if they are stage II or III patients who are estimated to receive chemotherapy and radiotherapy after surgery and advanced patients who cannot be treated surgically but can only undergo chemotherapy and radiotherapy, pregnancy should be terminated early because chemotherapy and radiotherapy should be terminated early. Because chemotherapy and radiotherapy affect the fetus, only termination of pregnancy can reduce the patient’s burden and meet the requirements of eugenics. Breast disease experts remind women of childbearing age to be fully aware of the symptoms of breast cancer during breastfeeding and to be more alert. Once a suspicious lump of breast appears during pregnancy or breastfeeding, they should go to hospital for examination in time.