Risk Factors

The average woman in the U.S. today has a 12.6 percent chance (or about one chance in 8) of developing breast cancer sometime during her life. Her risk at any one age, however, is far lower.

Gender

Breast cancer is much more common in women than in men. If you are a woman, you are at risk for breast cancer. About 1 percent of breast cancer cases occur in men.

Age

The chance of developing breast cancer increases with age. Eighty percent of all breast cancers are found in women over the age of 50. A woman in her 20s has a much lower risk of being diagnosed with breast cancer than does an older woman. Your risk of developing breast cancer by age is listed below:

Personal History

A woman who has had cancer in one breast is more likely to develop it in the other.

Menstrual History

A woman who began having menstrual periods early (before age 12) or went through menopause late (after age 50) has a higher than average risk of breast cancer. Doctors believe this may be related to the overall amount of estrogen the breast is exposed to over a lifetime.

Reproductive History

Women who had their first child after the age of 30 or who had no children are at increased risk for disease. This may be due to protective maturational changes in the breast tissue that occur with full-term pregnancy.

Family History

A woman is two to three times more likely than the general population to develop breast cancer if a first-degree relative (mother, sister) has had the disease. If both her mother and sister had breast cancer, the risk is even higher. This increased risk is highest when the relatives developed cancer at a young age (before the onset of menopause) or developed it in both breasts.

In most cases, this increased familial risk is not due to the much-discussed breast cancer genes known as BRCA1 and BRCA2. Those genes are responsible for only about 5 to 10 percent of all breast cancers. The increase in risk seen among family members is more commonly due to a more generalized tendency to develop the cancer, such as having a heightened sensitivity to radiation or to a particular carcinogen.

Benign Breast Disease

Some types of non-cancerous breast diseases can raise a woman's risk for breast cancer. These include atypical hyperplasia, in which abnormal (but not cancerous) cells are overproduced; and lobular carcinoma in situ, in which atypical cells are overproduced in the lobules. A history of breast cysts or fibrocystic changes does not increase the risk for breast cancer.

Estrogen Replacement Therapy

Taking replacement hormones after menopause begins seems to raise the risk of disease very slightly, but the added risk disappears about five years after stopping the hormones.

Oral Contraceptives

Taking the birth control pill also raises the risk of breast cancer very slightly, but the increased risk disappears about ten years after a woman stops taking the pill.

Alcohol

Having more than one alcoholic drink a day may increase the risk of breast cancer, particularly when a woman begins drinking under the age of 30.

Weight/Diet

Obesity leads to a higher risk of breast cancer in postmenopausal women, perhaps because fat cells produce excess estrogen. One study found that the risk of breast cancer was 40 percent higher in women who gained 44 to 55 pounds after the age of 18. Studies of fat content in the diet have led to contradictory results. Studies that compared women around the world found that those who lived in countries with typically high fat diets had higher rates of breast cancer. But studies that looked at women's diets in the U.S. have been mixed and did not find any consistent relationship between fat in the diet and breast cancer risk.

Exercise

There is some evidence that exercise might lower a woman's risk for breast cancer.

Radiation Exposure

Exposure to radiation, particularly during the first two or three decades of life, has been associated with an increased risk of breast cancer. (Exposure to low-dose mammography radiation in women over 40, however, is known to pose little risk.)

Pesticides & Pollutants

To date, there are no known links between pollutants and breast cancer risk, but studies are ongoing.