The average woman in the US today has a 12.6 percent (about one in eight) chance of developing breast cancer by the time she reaches her 80s. Her risk is lower when she is younger and increases as she ages. For example, women in their 30s have a 1 in 233 chance of developing breast cancer, while the risk for women in their 60s is 1 in 27.
In addition to heredity, several other factors have been associated with a slightly increased risk of developing breast cancer:
Breast cancer is much more common in women than in men. Only about 1 percent of breast cancer cases occur in men.
The chance of developing breast cancer increases with age. Eighty percent of all breast cancers are found in women over the age of 50.
Personal Medical History
A woman who has had cancer in one breast is more likely to develop it in the other.
A woman who began having menstrual periods early (before age 12) or went through menopause late (after age 50) has a slightly higher than average risk of breast cancer. This may be related to the overall amount of estrogen the breast is exposed to over a lifetime.
Women who had a first child after the age of 30 or who never had children have a slightly higher risk for the disease. This may be due to protective changes in breast tissue that occur with full-term pregnancy.
Benign Breast Disease
Some types of noncancerous breast conditions may be an indication of an increased risk for breast cancer — including atypical hyperplasia, in which abnormal 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 of breast cancer.
Estrogen Replacement Therapy
Taking replacement hormones after the beginning of menopause slightly raises the risk of disease, but the added risk disappears about three to five years after stopping the hormones. Moreover, the risk has been shown to be specific to combination hormone replacement therapy with both estrogen and progestin, compared to estrogen alone.(1),(2)
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.
Increasing evidence suggests that regular alcohol intake (the equivalent of one drink daily, over time) may slightly increase the risk of breast cancer. Having two or more drinks per day further increases risk.(3)
Research shows that being overweight or obese, particularly after menopause, increases the risk of breast cancer and recurrence. Having excess fat tissue may increase breast cancer risk by increasing estrogen levels. Overweight is defined as having a body mass index (BMI) of 25 or greater. Obesity is defined as having a body mass index (BMI) of 30 or greater. Speak with your doctor or a registered dietitian to learn more.
For now, doctors recommend following a healthful diet: a variety of vegetables and fruits, whole grains, and lean proteins; limited alcoholic beverages; and appropriate total calories to achieve and maintain a healthy weight. If you have questions or would like individual guidance, including whether or not you should be taking dietary supplements, speak with a registered dietitian.
Engaging in regular exercise is also a key component of good health. It helps to achieve and maintain an ideal body weight and may reduce breast cancer risk and improve survival among women diagnosed with the disease.(4),(5)
Exposure of breast tissue to radiation, particularly during the first two or three decades of life, has been associated with an increased risk of breast cancer. The amount of radiation from a mammogram, however, is very small and does not increase risk.