Many advances have been made in epidemiological and laboratory studies on the etiology of breast cancer at home and abroad, but so far, the etiology has not been fully understood and the role of various risk factors in the development of breast cancer is still being explored. The purpose of studying breast cancer and its related factors is to find the causes of its development, suggest high-risk factors, and monitor the high-risk group, so as to achieve the three early detection, early diagnosis, and early treatment and intervention control, and open up new ways for the prevention and treatment of breast cancer. Most scholars believe that early onset of menstruation, late age at first birth, late age at menopause, family history of breast cancer, history of benign breast disease, and the contralateral breast of breast cancer patients are high risk factors for the development of breast cancer. Other factors associated with breast cancer are marriage, feeding, diet, lifestyle habits, obesity, certain medications, psychological factors and viral factors. Therefore, breast cancer is the result of the combined effect of many factors under certain conditions. The age of menarche is closely related to the nutrition and diet of children, and when nutrition is improved, the risk of breast cancer will gradually decrease. The age of menarche is closely related to children’s nutrition and diet, and with improved nutrition, the age of menarche will gradually advance, which may be related to the increasing incidence of breast cancer. In addition, the length of the menstrual cycle reflects the number of changes in hormone levels that a person experiences during his or her lifetime, and the shorter the menstrual cycle, the greater the number of changes and the greater the number of times the breast gland is stimulated by estrogen. The risk of breast cancer is increased by late menopause age. Some people have calculated that the risk of breast cancer is reduced by 50 for those who have menopause at the age of 45 compared to those who have menopause at the age of 55. Before menopause, the risk of breast cancer is large, while the risk of breast cancer after menopause is smaller, and the risk of breast cancer after menopause is only 1/6 of that of breast cancer before menopause. The incidence of breast cancer in the breast after artificial menopause is reduced. Women with long menopause and long irregular menstrual periods have an increased risk of breast cancer. Being unmarried is a risk factor for breast cancer and it has been proven that the incidence of breast cancer is higher in unmarried women, women who marry late and those who are married for a short duration. It is known that young age at menarche, late age at menopause and long duration of menstruation are independent risk factors for breast cancer. (b) Birth frequency and breastfeeding The results are not entirely consistent as to whether birth frequency is a factor affecting breast cancer. It has been suggested that a high number of breastfeeding months has a protective effect on the occurrence of breast cancer, which is considered to be caused by the confounding of the number of births, and in recent years, some studies have concluded that breastfeeding is an independent protective factor, especially for premenopausal women. However, more births require more opportunities for breastfeeding, and more breastfeeding cannot be considered as an important protective factor for breast cancer. (c) Benign breast diseases Whether cystic hyperplasia of the breast is a pre-cancerous lesion is still controversial, some people believe that this disease can disappear on its own after marriage or pregnancy after marriage, and even if it recurs, it can heal on its own after menopause. Breast fibroids have been considered not to increase the risk of breast cancer, but recent studies suggest that they tend to be a risk factor for breast cancer. （Breast cancer is an estrogen-dependent tumor and its development is closely related to endocrine dysfunction. The main source of estrogen is the ovaries, which secrete estrone, estradiol and estriol, which mainly act on the ducts of the breast. When ovaries secrete too much hormone and act on sensitive breast tissue for a long time, it can lead to proliferation of breast cells and cancer. Checking testosterone and dihydroandrosterone in the blood and urine of breast cancer patients, the mean values of androgens are higher than those of the control group. The prognosis of breast cancer patients with hypothyroidism or thyroid disease is poor, and thyroid surgery on stable breast cancer patients may cause sudden spread of cancer. (E) Exogenous factors In 1982-1988, WHO conducted a collaborative study and found that there is a relationship between contraceptive drugs and breast cancer, and the relative risk of breast cancer is higher in the fertile period than in the infertile period, and the relative risk of breast cancer is higher in the low social class than in the high social class. The WHO also analyzed the relationship between different types of contraceptives and different breast cancer by tissue type. The risk of breast cancer was increased for those without ovaries taking estrogen, not for those with ovaries taking estrogen for a short period of time, and increased for those who took it for more than 5 years for a long period of time. The relationship between daily doses and cumulative monthly doses and breast cancer in those with ovaries is not uniformly understood. Selenium levels have been examined and are lower in smokers than non-smokers, and lower in those with first menstruation less than 13 years old than those older than 13 years old. Another analysis showed that manganese and chromium levels in the hair of breast cancer patients were higher than in normal subjects. Breast cancer tissue contains several times more potassium than normal tissue. Whether these elements are the cause or the result of lesions in breast cancer needs to be further explored. (vi) Lifestyle habits High-fat diets can increase the incidence of breast cancer. The reason for the effect of high-fat diet on the risk of breast cancer may be that 1. long-term high-fat diet can change the status of intestinal bacteria, which can transform steroids from bile into carcinogenic estrogens through metabolism. 2. high-fat diet can increase the secretion of prolactin, which in turn increases the secretion of estrogen in the body. 3. fat can increase weight or even obesity, and the greater the weight, the higher the risk of breast cancer. 4. 4 Excessive nutrition can lead to early menarche and delayed menopause, and estrogen is derived from adipose tissue after menopause. In short, a high-fat diet can lead to early menarche and obesity, which can increase the risk of breast cancer. It has been studied that alcohol consumption increases the risk of breast cancer by 1.5 to 2.0 times. Biological studies suggest that ethanol affects the permeability of cell membranes and its metabolites have an irritating effect on the breast, but the risk of breast cancer caused by ethanol has not yet been determined. (vii) Virus In 1936, Bittner discovered a factor, mammary factor, in the milk of mice with breast cancer that could be passed on to their offspring. 1958, someone discovered this substance in murine breast cancer sections and classified it into two types, A and B, which is murine mammary tumor virus (MuMTV). 10 years later, Bermbaro proved that MuMTV is the type B virus particle, i.e., type B RNA virus.Schlom et al. (1971) also found a type B RNA virus particle in the milk of breast cancer patients with a morphology similar to that of the murine mammary factor MuMTV.Axel et al. (1972) reported the discovery of an RNA-dependent reverse transcriptase in the milk of breast cancer patients, which could only be found in the B particle of Hageman (1978) isolated four antigenic substances from patients’ breast cancer tissues that were related to MuMTV antigen, which strongly suggests the presence of MuMTV-related viruses in human breast cancer tissues. (viii) Heredity The prevalence of breast cancer in families has long been statistically proven, and the incidence of breast cancer in those with a family history of breast cancer is 3-5 times higher than that of the general population. The risk of breast cancer in daughters of mothers with breast cancer is 40 to 50 times higher than that in daughters with no family history. It is obvious that breast cancer has a tendency to run in families. The heritability of breast cancer induced by mother’s milk transmission in mice has been demonstrated in experiments with mice. Genetic evidence for human breast cancer is gradually increasing, and gene linkage analysis has identified chromosomal long and short arm exchange loci that may be associated with breast cancer sensitivity genes. Gene segregation analysis has revealed that breast cancer genotypes are transmitted in the same manner as chromosomal dominant inheritance. However, most breast cancer patients do not have a family history and most twins do not have the disease at the same time, suggesting that genes are not the sole cause of the disease. (ix) Body type Deward et al. reported that the incidence of breast cancer does not increase with age in menopausal women with thin body type, but some countries reported that the age at which obesity begins is related to breast cancer, and obesity is mostly unrelated to breast cancer at age below 50, while the risk of breast cancer increases by 80 for every 10 Kg increase in weight above 60 years of age. long-term physical exercise. Preventing weight gain and obesity can prevent the occurrence of breast cancer. (X) Radiation The data of the survivors of the atomic bombings in Japan and those exposed to medical X-rays show that high doses of radiation can increase the risk of breast cancer. The magnitude of breast cancer risk depends on the age and dose of radiation received. Generally, the age of 10-30 years is the most sensitive to the effects of radiation exposure during the active mitotic phase, and the risk is less after 30 years of age. The risk of breast cancer from radiation exposure in the first pregnancy is higher than either before or after this period, and in women who have not had children, the risk of breast cancer from radiation exposure is higher than in women who have had children. In conclusion, women are sensitive to radiation during menstruation and pregnancy. Regarding the latency period of breast exposure to radiation, it is estimated to be as short as 5 years and generally 10 to 15 years, with a longer latency period in young people than in older people. Low-dose radiation is used for breast screening, and the risk of breast cancer is very small. (xi) Years of education The longer the years of education, the higher the risk of breast cancer. It is generally believed that the high risk of breast cancer in people with long years of education is a combination of factors, and these people tend to marry late, give birth late, have fewer births, take oral contraceptives, have a high economic level, and have a good nutritional status, which all contribute to the occurrence of breast cancer. (xii) Mental effects When the nerves are strongly stimulated by anxiety and tension or depression, acting on the central nerves of the cerebral cortex, causing autonomic dysfunction and suppression of immune function, the immune mechanism to resist cancerous tumors can be suppressed. If the cerebral cortex is repeatedly stimulated by strong stimulation, the body is always in a state of tension, resulting in imbalance of the internal environment of the body, which will eventually affect the function of the body’s anti-cancer mechanism, and it has been shown that the increased risk of breast cancer is related to emotional disorders.