Breast Cancer

Breast cancer is the most commonly diagnosed cancer (other than skin cancer) in U.S. women, with more than 190,000 new diagnoses each year.

The suspicion of breast cancer may arise when a lump is detected in the breast or screening mammography reveals an abnormal area of the breast. In order to diagnose the cause of the suspicious area or lump, a physician may perform a biopsy. During a biopsy, a physician removes cells for examination in the laboratory to determine whether cancer is present. Other information obtained from the biopsy sample will play an important role in treatment decisions. If the biopsy indicates that cancer is present, additional surgery may be performed after the patient and doctor select a course of treatment.

Prevention and Screening

The chance of an individual developing cancer depends on both genetic and non-genetic factors. A genetic factor is an inherited, unchangeable trait, whereas a non-genetic factor is a variable in a person’s environment, which can often be changed. Non-genetic factors may include diet, exercise, or exposure to other substances present in our surroundings.

Heredity or Genetic Factors

Being Female: Ninety-nine percent of breast cancer diagnoses in the United States occur in women. Among both women and men, risk of breast cancer increases with age.

Family History: Women with a family history of breast cancer have a greater risk of developing breast cancer themselves. In addition, some families are at particularly high risk of cancer due to hereditary cancer syndromes. These families often have multiple family members with cancer, and are more likely to develop cancer at a young age. In the case of breast and ovarian cancers, inherited mutations in two genes—BRCA1 and BRCA2—have been found to greatly increase the lifetime risk of developing breast and ovarian cancer. Mutations in these genes can be passed down through either the mother’s or the father’s side of the family.

Breast Density: Breast density refers to the extent of glandular and connective tissue in the breast. Breasts with more glandular and connective tissue—and less fat—have greater density. Women with higher breast density are at increased risk of developing breast cancer. In addition, dense breasts make it more difficult to detect breast cancer by mammography.

Personal History of Breast Cancer or Benign Breast Disease: It is important to realize the women who have already had breast cancer are at increased risk for breast cancer in the opposite breast and that this increased risk persists for 20 years or more. Women with certain types of benign breast disease (such as atypical hyperplasia) also have an increased risk of developing breast cancer.

Environmental or Non-Genetic Factors

Reproductive Factors: Several reproductive factors have been associated with an increased incidence of breast cancer. These include an young age at first menstrual period, a late age at menopause, and a late age at the birth of the first child.

Postmenopausal Hormones: Results from the Women’s Health Initiative suggest that postmenopausal hormone therapy with a combination of estrogen and progestin increases the risk of breast cancer. Furthermore, as use of postmenopausal hormones has decreased, breast cancer incidence has also decreased; this provides additional support for a link between postmenopausal hormone use and risk of breast cancer.

Alcohol: Moderate alcohol consumption (often defined as two or more drinks per day) has consistently been linked with an increased risk of breast cancer.

Obesity: In premenopausal women, obesity has been linked with a decreased risk of breast cancer, possibly as a result of disrupted menstrual cycles and altered hormone levels. In postmenopausal women, however, obesity has consistently been linked with an increased risk of breast cancer. The link between obesity and postmenopausal breast cancer appears to be strongest among women who have never used postmenopausal hormone therapy, and may be explained by the higher estrogen levels in obese postmenopausal women. Studies have shown that weight gain in women during adult life increases the risk of postmenopausal breast cancer.

Radiation: Women who have received radiation to the chest for the treatment of Hodgkin’s lymphoma or other cancers appear to have an increased risk of breast cancer. A study has also shown that women who have received low or high dose radiation to the chest have an increased risk of developing breast cancer. Therapeutic doses of radiation have long been known to increase the risk of developing breast cancer. However, this study suggests that diagnostic procedures, such as periodic chest X-rays, can also increase the risk of developing breast cancer.

DES: Diethylstilbestrol (DES) is a synthetic estrogen that was used frequently in pregnant women between the 1940s and 1960s. The drug was used to reduce the risk of miscarriages, though later studies indicated that it probably had no effect on miscarriage risk. In 1971 a study reported that girls born to women who had used DES (DES daughters) had a greatly increased risk of developing a certain type of vaginal cancer. More recent research suggests that DES daughters may also have an increased risk of breast cancer.

Lack of Exercise: Several studies have shown that women who exercise regularly have a lower risk of developing breast cancer than women with less physical activity. One study involving over 100,000 women reported that long-term physical activity reduced the risk breast cancer by one third.


Although many questions remain about the causes and prevention of breast cancer, research suggests that certain behaviors are likely to reduce risk.

Limit Alcohol Consumption: Regular alcohol consumption has consistently been linked with a modest increase in risk of breast cancer; by limiting alcohol intake women are likely to reduce their risk of breast cancer as well as several other types of cancer.

Achieve or Maintain a Healthy Body Weight: Excess body weight has been linked with an increased risk of breast cancer in postmenopausal women.24 By achieving or maintaining a healthy weight, women may reduce their risk of breast cancer and other common, chronic health problems.
Engage in Regular Physical Activity: Life-long physical activity is an important component of cancer prevention, and several studies suggest that regular physical activity may decrease the risk of developing breast cancer.

Breastfeed: Long-term breastfeeding has been linked with a modest reduction in breast cancer risk.