The development of breast cancer is the result of multiple factors, and no single factor can explain the development of breast cancer. Breast cancer may be the result of a combination of factors under certain conditions.
1. Menstruation and marriage
Early menarche is an important risk factor for breast cancer. It is believed that the risk of breast cancer is more than 4 times higher for those who have menarche before the age of 12 than for those who have menarche after the age of 13, but it is usually believed that the risk of breast cancer can be reduced by about 20% if menarche is one year later. The age of menarche is closely related to children’s nutrition and diet, and improved nutrition will gradually lead to an earlier age of menarche, which may be associated with an increased 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 risk of breast cancer. Being unmarried is a risk factor for breast cancer. It has been shown that the incidence of breast cancer is high among unmarried women, women who marry late and those who have a short duration of marriage. Li Funian, Breast Disease Treatment Center, Affiliated Hospital of Qingdao University
2.Birth and breastfeeding
Whether the number of births is a factor directly affecting breast cancer or not, the results are not entirely consistent. Foreign scholars believe that the incidence of breast cancer is extremely low if the number of births is more than 4. The high number of births has a protective effect on breast cancer, probably because the placenta has a large amount of estriol (E3) production, which has a protective effect on women. It has been suggested that a high number of months of breastfeeding has a protective effect on the occurrence of breast cancer, which is considered to be caused by the confounding of the number of births. In recent years, some studies have suggested that breastfeeding is an independent protective factor, especially for premenopausal women. However, more births require more opportunities for breastfeeding, and not breastfeeding cannot be considered as an important protective factor for breast cancer.
3. Benign breast disease
It is still controversial whether cystic hyperplasia of the breast is a pre-cancerous lesion. In the 1980s, it was thought that the risk of breast cancer could be increased by 3-6 times due to benign breast diseases, with cystic hyperplasia and breast fibroids being the most important ones. The incidence of breast cancer in patients with cystic hyperplasia is 3 to 4 times higher than in those without cystic hyperplasia, and pathological examination confirms that about 20% to 30% of breast cancer patients have cystic hyperplasia.
In the literature, the cancer rate of cystic hyperplasia is reported to be 2% to 4%, and the incidence of breast cancer is reported to be 2 to 3 times higher in patients with cystic hyperplasia, and this risk may persist up to 30 years after the diagnosis of cystic hyperplasia. 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.
4. Endogenous factors
Breast cancer is an estrogen-dependent tumor and its development is closely related to endocrine dysfunction. Estrogen mainly comes from the ovary, which secretes three components: estrone (E1), estradiol (E2) and estriol (E3), mainly acting on the breast ducts. When the ovaries secrete too much hormone and act on sensitive breast tissue for a long time, it can lead to proliferation and cancer of breast cells. The total plasma hormone level of breast cancer patients increases by 15% compared with normal women, and the E2 level of postmenopausal women can be 30% higher. Overseas (1985) reported that the free E2 level in premenopausal breast cancer patients was significantly higher than that of normal people.
5.Exogenous factors
(1) Research data from foreign scholars indicate that women under 45 years of age who take birth control pills after their first birth have an increased risk of breast cancer as the duration of taking birth control pills increases, and that taking birth control pills under 25 years of age increases the risk of breast cancer. However, other studies have found no significant increase in breast cancer in women taking oral contraceptives. Because of the inconsistent results of various studies, further research is needed to show the relationship between the age at which women start taking contraceptives and the subsequent occurrence of breast cancer.
(2) The risk of breast cancer was increased by estrogen in those without ovaries, and was not associated with breast cancer in those with ovaries who took estrogen for a short period of time, and increased in those who took it for more than 5 years. The relationship between the monthly dose and cumulative monthly dose of estrogen and breast cancer in those with ovaries is not yet consistent.
6. Lifestyle habits
High fat diet may increase the incidence of breast cancer.
7. Genetic factors
It has been statistically proven that the incidence rate of breast cancer is 3-5 times higher in people with family history of breast cancer than in the general population. In clinical practice, we often see mothers and daughters or sisters suffering from breast cancer at the same time or successively, and the age of onset is 10 to 20 years earlier in the second generation. The risk of breast cancer in daughters of mothers with breast cancer is 40 to 50 times higher than that of those without family history. It is obvious that breast cancer has a tendency to run in families.
8. Body shape
The incidence of breast cancer does not increase with age in menopausal women with thin body shape, but in some countries, the age of obesity is related to breast cancer, and it is not related to breast cancer when the age of obesity is below 50, while the risk of breast cancer increases by 80% for every 10 kg increase in weight above 60. Long-term physical exercise, to prevent weight gain and obesity, can prevent the occurrence of breast cancer.
9.Radiological effects
The survivors of the atomic bombings in Japan and the people exposed to medical X-ray show that high doses of radiation can increase the risk of breast cancer. U.S. watchmakers because of the dial of the luminous irradiation of the radium issued by the radiation, resulting in an increased risk of breast cancer. The risk of breast cancer depends on the age and dose of radiation received.
Generally, the age of 10 to 30 is the active mitotic stage, which is the most sensitive to the effect of radiation exposure, and the risk is less after 30; the risk of breast cancer from radiation exposure in the first pregnancy is higher than before or after this period; the risk of breast cancer from radiation exposure in women who have not given birth is higher than that of women who have given birth. In conclusion, women are sensitive to radiation during menstruation and pregnancy.
10.Years of education
The longer the years of education, the higher the risk of breast cancer. The survey of Tianjin Cancer Institute showed that the risk of breast cancer is 3.6 times higher for those with university education than those without university education. The higher risk of breast cancer in people with long years of education is a combination of factors. These people tend to marry late, give birth late, have fewer births, take oral contraceptives, have high economic level and good nutritional status, which all contribute to the occurrence of breast cancer.
11.Spiritual effect
When the nerves are strongly stimulated by anxiety, tension or depression, which act on the central nerves of cerebral cortex, causing autonomic nerve function disorder and immune function suppression, the immunity against cancer tumor can be inhibited. If the cerebral cortex is repeatedly stimulated by strong stimulation, the body is always in a state of tension, resulting in an imbalance of the body’s internal environment, which will eventually affect the function of the body’s anti-cancer mechanism. Studies have shown that the increased risk of breast cancer is associated with emotional disorders.