Age. The risk of developing breast cancer increases as a woman ages, with the majority of breast cancers developing in women over the age 50. At age 30, a woman's risk of developing breast cancer is one in 2,525. By age 50, her chances are one in 50, rising to one in 14 by age 70.
Race. Although white women are more likely to develop breast cancer, black women are more likely to die from the disease. The reasons for this are unclear and probably involve both socioeconomic and biologic factors.
Previous history of breast cancer. Women who have had breast cancer in one breast have three to four times the risk of breast cancer in their opposite breast.
A history of endometrial or ovarian cancer. The development of these cancers is also associated with exposure to hormones and, therefore, a woman's risk of breast cancer may also be increased. Some BRCA1 or BRCA2 gene mutations may also increase the risk of both ovarian and breast cancers.
A family history of breast cancer. Women who have a first-degree relative (mother, sister, daughter) diagnosed with breast cancer are at increased risk of the disease. More than one first-degree relative with breast cancer elevates that risk.
A genetic predisposition. Mutations to the BRCA1 or BRCA2 genes are associated with increased breast cancer risk. Screening tests are available to test for known mutations to these genes, but are not recommended for everyone and only following appropriate genetic counseling. Researchers estimate that breast cancers caused by these genes make up only 2% to 3% of all breast cancers.
Estrogen exposure. Estrogen is a hormone in women that controls the development of secondary sex characteristics (such as breast development). A woman's production of estrogen decreases at menopause. Doctors think that exposure to estrogen for a long time may increase breast cancer risk:
-
- A long menstrual history: Women who began menstruating before age 12 or went through menopause after age 55 have a higher risk of breast cancer because their breast cells have been exposed to estrogen for longer periods of time.
- Late or no pregnancies: Women who have their first pregnancy after age 30 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.
- Estrogen in medication: Recent use of oral contraceptives or hormone replacement therapy (HRT), or long-term use of HRT, may increase a woman's risk of breast cancer.
Atypical hyperplasia. This is a condition characterized by abnormal, but not cancerous, cells. Atypical hyperplasia is a risk factor of breast cancer.
Lobular carcinoma in-situ. This is associated with an increased risk of developing a cancer in either breast when found within an otherwise benign breast biopsy.
Lifestyle factors. As with other types of cancer, studies continue to show that various habits may contribute to the development of breast cancer. These include:
-
- Obesity: According to a new study, being obese or even overweight increases a woman's risk of breast cancer.
- Lack of exercise: Exercise lowers hormone levels and boosts the immune system; lack of exercise contributes to obesity.
- Alcohol use: Drinking more than one alcoholic drink per day may raise 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, patients with lymphoma treated with radiation therapy to the chest, patients undergoing large numbers of x-rays for tuberculosis or non-malignant conditions of the spine, and children treated with radiation for tinea capitis (ringworm).
