What might influence my getting breast cancer?

This much is known about how women get breast cancer, according to the American Cancer Society:
•Fewer than 15 percent of women who are diagnosed have close female relatives with the disease
•Aging is a factor. About 80 percent of women are over age 50 when they're diagnosed. Women in their 30s make up only 3.5 percent of cases.
•Breast cancer is influenced by estrogen production, so women who started menstruating young (before age 12) or began menopause late (after 55) have a slightly increased chance of getting it.
•Never bearing children or having them after age 30 carries a higher risk; women who have never breastfed are also at a slightly higher risk. The most protective time to have a baby is before the age of 20.The cancer society notes that it's been observed since the 19th century that breast cancer occurs with greater frequency in nuns, perhaps because they don't get pregnant. Some researchers suspect that lesbians also may be at greater risk than heterosexual women because they are more likely to have never been pregnant. A study funded by the California Breast Cancer Research Program is examining the issue of breast cancer in lesbians.
•White women are a bit more susceptible to developing breast cancer, but African-Americans are more likely to die from it because they are often diagnosed at a late stage.
•Taking estrogen replacement after menopause may also lead to an increased risk of developing cancerous breast tumors, according to numerous studies comparing women who took hormone replacement drugs with those who did not. One study published in the journal Menopause showed that women who took hormone replacement therapy and oral contraceptives had three times the risk of breast cancer as women who took no hormone drugs. And a study published in the July 17, 2002 issue of the Journal of the American Medical Association said that after five years, the health risks of hormone replacement therapy (HRT) outweigh the benefits.
Known as the Women's Health Initiative, the study of women taking a combination of estrogen and progestin (synthetic progesterone) was halted three years early in May 2002, when researchers found that the women who took HRT had invasive breast cancer rates 26 percent higher than women who didn't take hormones. The women on HRT also experienced rates for stroke that were 41 percent higher and heart disease rates that were 29 percent higher than women on placebo, or dummy pills.
However, the group on HRT experienced a 24 percent reduction in the rate of hip fractures, further bolstering the notion that hormone replacement is protective against osteoporosis.
•One lifestyle factor that has a clear link to breast cancer in study after study is alcohol consumption. Those findings were reconfirmed in 2000 by researchers with the Canadian National Breast Screening study, which analyzed the drinking habits of 1,336 women with breast cancer and compared them to more than 5,000 women without the disease. Breast cancer was associated with very high levels of alcohol consumption: Women who had four or five drinks a day were 1.7 times more likely to develop the disease. More moderate drinking appeared not to instigate the disease, however, based on previous studies, the American Cancer Society urges women to limit alcohol to one drink a day.
•A recent report in the Journal of the National Cancer Institute suggests that smoking may increase a woman's risk of breast cancer by about 30 percent. Other factors under study are diet (especially saturated fat intake), being overweight (because estrogen is stored in fat cells), and exposure to x-rays and environmental pollutants. Asian women tend not to get breast cancer in their own countries, which some researchers link to a low-fat diet. American women tend to consume more fat than women in Asian countries, but science has been unable to prove a clear connection between dietary fat and breast cancer.
•A study reported in the Journal of the American Medical Association in February 2004 suggests there is a link between antibiotic use and breast cancer. Women in the study who had used antibiotics for a total of 1 to 500 days were about twice as likely to develop breast cancer than women who had never used antibiotics. Does this mean that antibiotics cause breast cancer? Researchers say there's no evidence that this is the case. Because there are so many variables to consider -- like the many reasons for taking antibiotics in the first place and the complicated ways that antibiotics affect various bodily processes -- more research is needed to understand what the link between antibiotics and breast cancer really means.
One theory is that women who take antibiotics also have lowered immunity systems that may predispose them to breast cancer, researchers said. Another possibility is that antibiotics kill off bacteria in the stomach that may protect women from cancer. Researchers said the data should be used to discourage doctors from overprescribing antibiotics, but should not discourage patients who need antibiotics for serious infections from taking them. They are encouraging further research on a possible link; in the meantime, women should not stop taking prescribed antibiotics and should discuss any concerns with their doctors.
Brenner notes that many risk factors are out of our control. Women can't influence when they started menstruating or reached menopause, and deciding whether and when to have children -- especially before age 20 -- is by no means a recommended or legitimate form of disease prevention.