Many epidemiologic studies have shown an increased risk of breast cancer associated with alcohol consumption. Individual data from 53 case-control and cohort studies were included in a British meta-analysis. Compared with women who reported no alcohol consumption, the RR of breast cancer was 1.32 (95% CI, 1.19-1.45; P < .001) for women consuming 35 g to 44 g of alcohol per day and 1.46 (95% CI, 1.33-1.61; P < .001) for those consuming at least 45 g of alcohol per day. The RR of breast cancer increases by about 7% (95% CI, 5.5%-8.7%; P < .001) for each 10 g of alcohol (i.e., one drink) consumed per day. The same result was obtained, even after additional stratification for race, education, family history, age at menarche, height, weight, BMI, breast-feeding, oral contraceptive use, menopausal hormone use and type, and age at menopause.
Factors Associated With Decreased Risk of Breast Cancer
Active exercise may reduce breast cancer risk, particularly in young parous women.Numerous observational studies have examined the relationship between physical activity and breast cancer risk. Most of these studies have shown an inverse relationship between level of physical activity and breast cancer incidence. The average RR reduction is reportedly 30% to 40%. However, it is not known to what degree, if at all, the observed association is to the result of confounding variables, such as diet or a genetic predisposition to breast cancer. A prospective study of more than 25,000 women in Norway suggests that doing heavy manual labor or exercising 4 or more hours per week is associated with a decrease in breast cancer risk. This decrease is more pronounced in premenopausal women and in women of normal or lower-than-normal body weight. In a case-control study of African American women, strenuous recreational physical activity (>7 hours per week) was associated with decreased breast cancer incidence.
Interventions Associated With Decreased Risk of Breast Cancer: Benefits and Harms
Selective estrogen receptor modulators (SERMs)
Data from adjuvant breast cancer trials using tamoxifen have shown that tamoxifen not only suppresses the recurrence of breast cancer but also prevents new primary contralateral breast cancers. Tamoxifen also maintains bone density among postmenopausal women with breast cancer.[70,71,72,73,74] Adverse effects include hot flashes, venous thromboembolic events, and endometrial cancer.[75,76,77]
These adjuvant trial results were the basis for the Breast Cancer Prevention Trial (BCPT) that randomly assigned 13,388 patients at elevated risk of breast cancer to receive tamoxifen or placebo.[78,79] The independent Endpoint Review, Safety Monitoring, and Advisory Committee closed the study early because of a 49% reduction in the incidence of breast cancer for tamoxifen-treated versus placebo-treated participants. After about 4 years of follow-up, placebo-treated women had 154 cases of invasive breast cancer compared with 85 cases in women who received tamoxifen. Noninvasive breast cancers were also reduced, with 59 cases in the placebo group versus 31 in the tamoxifen-treated group. Another benefit of tamoxifen use was a reduction in fractures, with 47 occurring in the tamoxifen-treated women compared with 71 in the placebo group. These benefits were accompanied by an increased incidence of endometrial cancer and thrombotic events in women aged 50 years and older. There were 33 endometrial cancers and 99 vascular events (including 17 cases of pulmonary embolism and 30 cases of deep vein thrombosis) in women who received tamoxifen compared with 14 endometrial cancers and 70 vascular events (including 6 cases of pulmonary embolism and 19 cases of deep vein thrombosis) in women who received a placebo.