The risk factors of breast cancer are unknown, although studies suggest that estrogen, the female hormone produced by the ovaries, is involved. One reason for suspecting estrogen is the association of breast cancer to certain reproductive system changes in a woman's life.
About 5% -10 % (per ACS literature) of all breast cancers are thought to be related to genetic predisposition. Molecular tests are available to identify BRCA1 and BRCA2 genetic susceptibility, which is present in a small percentage of the population. BRCA1 and BRCA2 mutations are seen more often in women of Jewish ancestry.
It has already been established that women with first-degree relatives who had breast cancer are at greater risk of getting it themselves. These women are encouraged to have screening tests earlier and sometimes more often than women without such a family history.
The risk of breast cancer increases with age. The lifetime risk is approximately 1 in 8. The risk increases significantly after age 50 with the risk for 50-year-olds at 1 in 37; 60-year-olds 1 in 26 and for 70-year-olds 1 in 24. Risk is higher in women who have a personal or family history of breast cancer, biopsy-confirmed atypical hyperplasia, increased breast density, a long menstrual history (menstrual periods that started early and ended late in life), obesity after menopause, recent use of oral contraceptives or postmenopausal estrogens and progestin, who have never had children or had their first child after age 30, or who consume alcoholic beverages.
Worldwide, breast cancer incidence rates appear to correlate with variations in diet, especially fat intake, although the specific dietary factors that affect breast cancer have not been firmly established. Vigorous physical activity and maintenance of a healthy body weight are associated with lower risk. Most data indicate tamoxifen decreases breast cancer risk and preliminary data suggest another selective estrogen-receptor modulator, raloxifene, does also.