Breast Cancer: Risk Factors

One in eight women in the U.S. will be diagnosed with breast cancer in their lifetime and over 220,000 women are diagnosed each year.

In recent years, there has been a gradual reduction in breast cancer incidence rates among women aged 50 or older. Death rates from breast cancer have also been declining since about 1990, in part to better due to screening and early detection, and the development of better treatment options. There are over 2 million breast cancer survivors today.

Risk factors for developing breast cancer include:

Gender Breast cancer is the most commonly diagnosed cancer in women. It is rare in men, with approximately 2,150 cases diagnosed each year. The reason is probably that men have less of the “female” hormones estrogen and progesterone, which can promote the growth of breast cancer cells.

Age About 20% of invasive breast cancers are discovered in women younger than age 50. Therefore, the majority of breast cancers occur in older postmenopausal women.

Genetic factors Between 5 percent and 10 percent of breast cancers are thought to be hereditary, meaning that they result directly from defects or mutations in the genes. This defect is hereditary, meaning that it can be passed on by a parent.

The BRCA1 and BRCA2 genes are the most common cause of hereditary breast cancer. Under normal circumstances, these genes help prevent cancer. Their job is to make proteins that keep the cells from growing abnormally, but when these genes are damaged, they do not function properly.

Women carrying inherited mutations in the BRCA1 and BRCA2 genes have an extremely high lifetime risk for developing breast and/or ovarian cancer. Moreover, breast cancer occurs at an earlier age in these patients. More pathological features have also been reported in breast cancers occurring in BRCA1 mutation carriers. Read more here about our genetic counseling program.

Family history A first-degree relative (mother, sister, or daughter) with breast cancer roughly doubles a woman's risk. Two first-degree relatives with breast cancer increase a woman’s risk about three times. Women with a father or brother diagnosed with breast cancer, also have an increased risk. However, it is important to note that 80% of all women diagnosed with breast cancer do not have a family history of this disease.

Personal history A woman with cancer in one breast has almost a 7-fold greater chance of developing a new cancer in the other breast or in another part of the same breast. This is considered an independent growth—not a recurrence (a return) of the first cancer.

Race White women have a slightly higher chance of developing breast cancer than African-Americans. Yet African-American women tend to develop more aggressive breast cancers at a younger age.

Asian, Hispanic, and Native-American women have a lower risk of developing breast cancer compared to non-Hispanic whites.

Dense breast tissue Women with dense breasts have a higher risk of breast cancer. Unfortunately, dense breast tissue can also make mammograms less accurate.

A number of factors affect breast density, such as age, menopausal status, the use of hormone replacement therapy during menopause, pregnancy, and genetics. A “dense” breast (as seen on a mammogram) has more glandular and fibrous tissue and less fatty tissue.

Benign breast conditions

  • Non-proliferative lesions generally don’t affect breast cancer risk, or may only increase it very little. These include simple cysts, what used to be called “fibrocystic changes”, certain benign tumors and calcifications, mild hyperplasia, a single papilloma, adenosis (non-sclerosing), ductal ectasia, periductal fibrosis, simple fibroadenoma, phyllodes tumor, squamous and apocrine metaplasia and fat necrosis.
  • Proliferative lesions without atypia are related to excessive growth of cells in the ducts or lobules of the breast tissue and appear to raise a woman's risk of breast cancer slightly (one and a half to two times normal). These conditions include complex fibroadenoma, sclerosing adenosis, several papillomas, and radial scars.
  • Proliferative lesions with atypia involve an overgrowth of cells in the ducts or lobules of the breast tissue, with some of the cells no longer appearing normal. These conditions, called atypical ductal hyperplasia (ADH), atypical lobular hyperplasia (ALH), or lobular neoplasia, elevate breast cancer risk to four to five times higher than normal.

Lobular carcinoma in situ (LCIS) In this condition, abnormal cells appear in the lobules of the milk-producing glands of the breast, but do not grow through the wall of the lobules. This diagnosis is linked to a seven to eleven-fold increased risk for developing invasive cancer (in either breast).

More years menstruating Women who started menstruating before age 12 and/or started menopause after age 55, have a slightly higher risk of breast cancer. This may be due to the body’s longer production of the hormones, estrogen and progesterone.

Not having children Women who haven’t had children or who gave birth after age 30 have a slightly higher risk for developing breast cancer, while those who’ve had several pregnancies and started their families as a younger age, have a reduced risk.

Oral contraceptives Women using oral contraceptives (birth control pills) have a slightly higher risk of breast cancer. This risk begins to drop once the pills are stopped, and to go back to normal 10 years after a woman has stopped taking these pills.

Post-menopausal Hormone Replacement Therapy (HRT) increases breast cancer risk.

Combined HT (the use of estrogen and progesterone) can elevate risk in as little as two years. It also increases the likelihood that the cancer may be found at a more advanced stage. However, a woman's breast cancer risk seems to return to that of the general population within five years of stopping combined treatment.

Alcohol Use One alcoholic drink a day carries a very small increase in breast cancer risk. Yet women who have two or more drinks daily have about a 20% higher risk of developing breast cancer than those who don’t drink at all.

Obesity/Overweight Breast cancer risk is greater for women who gained a significant amount of weight as adults but the risk may not be increased at all for women who have been overweight since childhood. Also, excess fat around the waist may have more of an impact on risk than fact around the thighs or hips.

Previous chest radiation Women who, in their childhood or adolescence, received radiation therapy to the chest to treat another cancer have a significantly increased risk for breast cancer. The chance of developing breast cancer from chest radiation is greater if the radiation was given when the patient’s breasts were still developing. Radiation treatment after age 40 does not seem to increase breast cancer risk. If the patient was treated with chemotherapy as well, this may have stopped ovarian hormone production long enough to lower risk.

Diethylstilbestrol (DES) exposure Until the 1960s the drug diethylstilbestrol (DES) was prescribed to pregnant women to lessen the chance of miscarriage (losing the baby). These women have a slightly increased risk of developing breast cancer. Women whose mothers took DES during pregnancy may have a slightly higher risk of breast cancer.