Risk Factors

A risk factor is anything that increases a person’s chance of developing cancer. Some risk factors can be controlled, such as physical activity and diet, and some cannot be controlled, such as age and family history. Although risk factors can influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. However, knowing your risk factors and communicating them to your doctor may help you make more informed lifestyle and health care choices.

Many cases of breast cancer occur in women with no obvious risk factors. This means that all women need to be aware of possible changes in their breasts and schedule a clinical breast examination (breast exam performed by a doctor or other health care professional) and mammogram (x-ray of the breast that can detect a tumor that is too small to be felt). It is likely that multiple risk factors influence the development of breast cancer.

The following factors may raise a woman’s risk of developing breast cancer:

Age. The risk of developing breast cancer increases as a woman ages, with most cases developing in women over 50.

Race and ethnicity. Although white women are more likely to develop breast cancer, black women are more likely to die from the disease. Reasons for survival differences are unclear and probably involve both socioeconomic and biologic factors.

Personal history of breast cancer. A woman who has had breast cancer in one breast has a 1% to 2% chance per year of developing a second breast cancer in her opposite breast.

Family history of breast cancer. Women who have a first-degree relative (mother, sister, daughter) diagnosed with breast cancer are at increased risk for the disease. More than one first-degree relative with breast cancer elevates that risk, especially if the cancer occurred before menopause. Women who have a second-degree relative (aunt, niece, grandmother, granddaughter) diagnosed with breast cancer also have a higher risk of breast cancer. The father’s (paternal) side of the family should also be considered equally to the mother’s (maternal) side when evaluating a family history. For example, you may be at higher risk if your father’s sister or mother had breast cancer.

Genetic predisposition. Mutations to the breast cancer genes 1 or 2 (BRCA1 or BRCA2) are associated with increased breast cancer risk. Blood tests (genetic testing) are available to test for known mutations to these genes, but are not recommended for everyone and only after a person has received appropriate genetic counseling. Men in families may also carry these gene mutations. Breast cancer in male family members significantly increases the risk of having a family breast cancer gene. Researchers estimate that breast cancers due to inherited genes with high risk for developing cancer make up only 5% to 10% of all breast cancers. If a woman learns she has these genetic mutations, there are steps she can take to lower her risk of breast and ovarian cancers. Learn more about the genetics of breast cancer.

Personal history of ovarian cancer. A history of ovarian cancer can increase a woman’s risk of breast cancer. Breast cancer gene mutations, such as BRCA1 or BRCA2, greatly increase the risk of both ovarian and breast cancers.

Estrogen and progesterone exposure. Estrogen and progesterone are hormones in women that control the development of secondary sex characteristics (such as breast development) and pregnancy. A woman’s production of estrogen and progesterone decreases at menopause. Prolonged exposure to these hormones increases breast cancer risk.

• Women who began menstruating before age 11 or went through menopause after age 55 have a higher risk of breast cancer because their breast cells have been exposed to estrogen and progesterone for a longer time.
  
  
• Women who have their first pregnancy after age 35 or who have never had a full-term pregnancy have a higher risk of breast cancer. Pregnancy may protect against breast cancer, because it pushes breast cells into their final phase of maturation.
  
  
• Recent use (within the past five years) and long-term use (several years or more) of postmenopausal hormone replacement therapy increases a woman’s risk of breast cancer.
  
  
• Removing the ovaries, a source of estrogen and progesterone, can greatly lower breast cancer risk; this procedure is called an oophorectomy. Some women with inherited BRCA1 or BRCA2 mutations undergo prophylactic oophorectomy as a preventive measure to lower their risk of breast and ovarian cancers.
  
  
• There is no clear link between the use of oral contraceptives (birth control pills) to prevent pregnancy and development of breast cancer.

Atypical hyperplasia of the breast. This condition increases the risk of breast cancer and is characterized by abnormal, but not cancerous, cells found in a breast biopsy.

LCIS. As explained in the Overview section, this condition describes abnormal cells found in the lobules or glands of the breast. LCIS increases the risk of developing invasive breast cancer (cancer that spreads into surrounding tissues). Talk with your doctor about the best way to monitor this condition.

Lifestyle factors. As with other types of cancer, studies continue to show that various lifestyle factors may contribute to the development of breast cancer.

• Recent studies have shown that postmenopausal women who are obese have an increased risk of breast cancer.
  
  
• Exercise lowers hormone levels, alters metabolism, and boosts the immune system. Increased physical activity is associated with a decreased risk of developing breast cancer.
  
  
• Regularly drinking more than one to two alcoholic drinks per day raises the risk of breast cancer.

Radiation. High doses of radiation may increase a woman’s risk of breast cancer. An increased risk of breast cancer has been observed in long-term survivors of atomic bombs, people with lymphoma treated with radiation therapy to the chest, people undergoing large numbers of x-rays (such as for tuberculosis or to treat residual thymic disease or acne), nonmalignant (noncancerous) conditions of the spine, and children treated with radiation therapy for ringworm. However, it should be noted that the amount of radiation a woman receives during a yearly mammogram does not seem to increase breast cancer risk and any slight risk is outweighed by the benefits of screening.