Breast cancer is one of the most common malignant tumors in women. It accounts for 7% to 10% of all malignant tumors in China and is on the rise year by year. Some major cities report that breast cancer is the first malignant tumor among women. The etiology of breast cancer is still unclear. The breast is the target organ of many endocrine hormones, such as estrogen, progesterone, general surgery center of PLA 302 Hospital Chu Yanqui and lactogen, among which estrone and estradiol are directly related to the development of breast cancer. Early age of menarche, late age of menopause, infertility and age of first full-term delivery are all associated with the development of breast cancer. The risk of breast cancer in first-degree relatives is two to three times higher than that of the general population. The relationship between benign breast disease and breast cancer is still debated, but most believe that high epithelial hyperplasia or atypical hyperplasia in the lobules of the breast may be associated with the development of breast cancer. In addition, overnutrition, obesity, and fatty diet may enhance or prolong the stimulation of estrogen on breast epithelial cells, thus increasing the chance of incidence. The incidence of breast cancer in North America and Northern Europe is about four times higher than that in Asia, Africa and Latin America, and the incidence of breast cancer in the second and third generation of immigrants gradually increases after the residents of low incidence areas move to high incidence areas, suggesting that environmental factors and lifestyle have a relationship with the development of breast cancer.