In general, what factors increase or decrease the chance of developing breast cancer and/or ovarian cancer?

The following factors have been associated with increased or decreased risk of developing breast and/or ovarian cancer in the general population. It is not yet known exactly how these factors influence risk in people with BRCA1 or BRCA2 mutations. In addition, a significant portion of hereditary breast cancers are not associated with BRCA1 or BRCA2 mutations.

  • Age—The risks of breast and ovarian cancer increase with age. Most breast and ovarian cancers occur in women over the age of 50. Women with harmful BRCA1 or BRCA2 mutations often develop breast or ovarian cancer before age 50.
  • Family History—Women who have a first-degree relative (mother, sister, or daughter) or other close relative with breast and/or ovarian cancer may be at increased risk of developing these cancers. In addition, women with relatives who have had colon cancer may be at increased risk of developing ovarian cancer.
  • Medical History—Women who have already had breast cancer are at increased risk of developing breast cancer again, or of developing ovarian cancer.
  • Hormonal Influences—Estrogen is a hormone that is naturally produced by the body and stimulates the normal growth of breast tissue. It is thought that excess estrogen may contribute to breast cancer risk because of its natural role in stimulating breast cell growth. Women who had their first menstrual period before the age of 12 or experienced menopause after age 55 have a slightly increased risk of breast cancer, as do women who had their first child after age 30. Each of these factors increases the amount of time a woman’s body is exposed to estrogen. Removal of a woman’s ovaries, which are the main source of estrogen production, reduces the risk of breast cancer. Breast-feeding also reduces breast cancer risk and is thought to exert its effects through hormonal mechanisms.
  • Birth Control Pills (Oral Contraceptives)—Most studies have shown a slight increase or no change in risk of breast cancer among women taking birth control pills. In contrast, numerous studies have shown that taking birth control pills decreases a woman’s risk of developing ovarian cancer. This protective benefit appears to increase with the duration of oral contraceptive use and persists up to 25 years after discontinuing use. It also appears that the use of birth control pills lowers the risk of ovarian cancer in women who carry harmful BRCA1 or BRCA2 mutations.
  • Hormone Replacement Therapy—Doctors may prescribe hormone replacement therapy (HRT) to reduce the discomfort of certain symptoms of menopause, such as hot flashes. However, the results of the Women’s Health Initiative (WHI), a large clinical study conducted by the National Heart, Lung, and Blood Institute, part of the National Institutes of Health (NIH), showed that HRT with the hormones estrogen and progestin is associated with harmful side effects, including an increased risk of breast cancer and increased risks of heart attack, blood clots, and stroke. The WHI also showed that HRT with estrogen alone was associated with increased risks of blood clots and stroke, but the effect on breast cancer risk was uncertain (27). In addition, the WHI showed an increase in ovarian cancer risk among women who received estrogen and progestin HRT, but this finding was not statistically significant. Because of these potential harmful side effects, the FDA has recommended that HRT be used only at the lowest doses for the shortest period of time needed to achieve treatment goals.

No data have been reported to date regarding the effects of HRT on breast cancer risk among women carrying harmful BRCA1 or BRCA2 mutations, and only limited data are available regarding HRT use and ovarian cancer risk among such women. In one study, HRT use did not appear to affect ovarian cancer risk among women with BRCA1 or BRCA2 mutations.

When considering HRT use, both the potential harms and benefits of this type of treatment should be discussed carefully by a woman and her health care provider.

  • Obesity—Substantial evidence indicates that obesity is associated with an increased risk of breast cancer, especially among postmenopausal women who have not used HRT. Evidence also suggests that obesity is associated with increased mortality (death) from ovarian cancer.
  • Physical Activity—Numerous studies have examined the relationship between physical activity and breast cancer risk, and most of these studies have shown that physical activity, especially strenuous physical activity, is associated with reduced risk. This decrease in risk appears to be more pronounced in premenopausal women and women with lower-than-normal body weight.
  • Alcohol—There is substantial evidence that alcohol consumption is associated with increased breast cancer risk. However, it is uncertain whether reducing alcohol consumption would decrease breast cancer risk.
  • Dietary Fat—Although early studies suggested a possible association between a high-fat diet and increased breast cancer risk, more recent studies have been inconclusive. In the WHI, a low-fat diet did not help reduce breast cancer risk.

Related Articles