The pathogenesis of cancer is not fully understood, and in 2015 there are two theories: 1. the risk of cancer in various tissues is related to its stem cell division number, and two-thirds of people develop cancer due to “bad luck”, that is, random mutations in DNA repair that occur in normal non-cancerous cells, and only one-third can be attributed to environmental factors or genetic predisposition. 2, while another proposes that “cancer is a product of evolution” and that in addition to mutational activation, cancer may require age-related tissue changes to obtain more favorable conditions for survival and thus win in competition with healthy cells. A healthy tissue ecosystem drives healthy cells to outcompete cancerous cells, and when the tissue ecosystem changes, such as through aging, smoking, or other stresses, cancerous cells can quickly adapt to the changed environment and be passed on from generation to generation through natural selection. Either theory points out that cancer is related to environmental factors and lifestyle, only in different proportions. Among the factors associated with breast cancer that we can change are: age at first birth, breastfeeding, exogenous estrogen, lifestyle factors, medications, etc. It is not easy to increase the absolute survival rate by 1%, but it is even more valuable to reduce the incidence rate by 1% (even if the treatment is perfect, the treatment is “traumatic”). The relationship between lifestyle and breast cancer is obvious: 1. Obesity and breast cancer: In 2014, the European Prospective Investigation Group on Cancer and Nutrition (EPIC) studied the relationship between weight change in middle-aged women (40-50 years old) and their risk of breast cancer around the age of 50. FINDINGS: Weight gain in middle-aged women increases the risk of breast cancer, and this relationship appears to be more significant for breast cancers diagnosed before the age of 50. The results of this study suggest that middle-aged women should control their weight in order to prevent breast cancer. 2014 British researchers Fourkala et al. found that the risk of breast cancer after menopause increased by 33% for women who increased their waist size every 10 years from age 25 to menopause. 2. Smoking and breast cancer: In 2014, the European Prospective Investigation Group on Cancer and Nutrition conducted a study to evaluate the relationship between passive and active smoking and invasive breast cancer, corrected for known risk factors for breast cancer. A total of 322988 women were enrolled, with 9822 women eventually developing breast cancer (of these, 183608 women who were passive smokers, with 6264 cases eventually developing breast cancer). The results showed that compared to women who never smoked and did not smoke passively, those who currently smoked (risk ratio HR=1,16 , 95% CI=1,05C1,28), formerly smoked (HR=1,14, 95% CI=1,04-1,25) and currently smoked (HR=1,10,95% CI=1,01-1,20) had an increased breast cancer risk. Breast cancer risk was higher for smoking between the first menstrual period and the first full-term pregnancy. A prospective cohort study from Canada in 2014 showed that smoking can be a high risk factor for breast cancer and that the risk of breast cancer is associated with the duration of smoking. The study included 89,835 women, aged 40-59 years, with a mean follow-up time of 22.1 months, and a total of 6,549 subjects developed breast cancer during the follow-up period. The results of the study found that the risk of developing breast cancer was related to the duration of smoking, the intensity of exposure, and cumulative exposure. Compared to women who smoked after pregnancy, women who smoked before their first pregnancy had a higher risk of breast cancer for the same number of years of smoking. This experiment affirmed that active smoking increases the risk of breast cancer in female patients, which also suggests that tobacco control should be an important element in the primary prevention of breast cancer. Alcohol and breast cancer: An increase in alcohol intake by one unit per day is associated with a 7-10% increase in breast cancer risk. In the Nurses’ Health Study, the risk of breast cancer increased by more than 15% for those who consumed 4-9 units of alcohol per week compared to those who did not drink alcohol. Higher intakers (27 units or more per week) had a 51% higher risk of breast cancer than non-drinkers. (1 unit is half a pint of 4% beer or fruit wine) 4. Mental stress: A study in Taiwan, China collected structured questionnaires from 157 breast cancer patients and 314 controls from June 2009 to June 2011 to investigate the relationship between psychological stress and lifestyle and breast cancer risk. The analysis showed that high mental stress (adjusted ratio ratio AOR= 1, 65; 95% confidence interval CI, 1, 10C2, 47), physical activity below 1000lcal per week (AOR=2, 17; 95% CI=1, 39C3, 39), and high intake of fried foods (AOR=1, 86; 95% CI=1, 24C2, 77) increased breast cancer risk. 5. Exogenous estrogens: The use of exogenous hormones increases the risk of breast cancer. A study conducted by Professor Prithwish De et al. of the Canadian Cancer Society showed a decreasing trend in hormone replacement therapy since 2002. The largest decrease in the use of combined hormone replacement therapy in women aged 50 to 69 years occurred between January 1, 2002 and December 31, 2004, from 12.7% to 4.9%. This decline coincided with a 9.6% reduction in breast cancer incidence. That is, the use of hormone replacement therapy may increase the risk of breast cancer in the Canadian group of women aged 50-69 years. There are opposite results: Professor Cerne and his team from Slovene conducted a study to evaluate the effect of the use of hormone replacement therapy (HRT) and some recognized risk factors for breast cancer on breast cancer incidence in postmenopausal women in Slovene. A total of 784 cases aged 50-69 years and 709 controls were enrolled in the study. The use of hormone replacement therapy reduced the risk of breast cancer. Moderate exercise may reduce the risk of breast cancer in postmenopausal women: A prospective French cohort study that included 59,000 postmenopausal women found that women who exercised moderately (simply walking at a comfortable pace for more than 30 minutes a day, or getting off the bus one stop earlier, or not driving to the store, and walking 4 hours a week) had a 10% lower risk of invasive breast cancer compared to less active women (HR=0,9). HR=0,9), especially among women who were active in the first 4 years after menopause. Some women who exercised moderately for 5-10 years before menopause, but slacked off during that time, did not have a reduced risk of breast cancer, suggesting that only consistent exercise can reduce breast cancer risk. Professor Phillips of Toronto Women’s University Hospital reviewed the literature on the association of body size and physical activity with breast cancer in BRCA mutations. Several studies have shown that healthy body size and physical activity (especially during adolescence) can reduce the risk of breast cancer in BRCA carriers. 7. Diet: Vegetables and fruits may reduce the incidence of cancer. Dietary antioxidant components: A prospective cohort study from the United States showed that people with higher dietary antioxidant components had a lower risk of breast cancer and that the effects of dietary antioxidants such as dietary carotenoids and flavonoids may be limited to certain subgroups, such as smokers and older adults.