Breast cancer is the growth of malignant tumors originating in breast tissue. A type of malignancy called invasive ductal carcinoma, which begins in the lining of the milk ducts, is the most common type of breast cancer. Less frequently, however, breast cancers may begin in the lining of the lobules (milk-producing glands).
Breast cancer can be treated most effectively if detected at an early stage when tumors are small and have not yet begun to spread to nearby lymph nodes or other parts of the body. Patients with early-stage cancer may have a very good prognosis. Once the cancer has begun to spread, breast cancer cases can become much more serious or even life-threatening.
What are the Risk Factors of Breast Cancer?
Breast cancer risk involves a mix of factors that a patient cannot control, such as gender and genetics, along with factors that are variable, including environmental conditions and lifestyle choices. Among the risk factors are:
- Age at First Menstrual Period—If a woman began menstruating before age 12, her breast cancer risk is slightly increased.
- Age at Menopause—A slight increase in breast cancer risk is associated with late menopause onset (after age 55).
- Age—As women age, their risk of developing breast cancer increases. Two out of three breast cancer cases are in women age 55 or older. Women under 45 account for 12.5 percent of female breast cancer cases.
- Dense Breast Tissue—Women who have a higher proportion of glandular tissue and less fatty tissue in their breasts are at higher risk of breast cancer. Since dense breast tissue may also make breast cancer more difficult to detect in a mammogram, other screening methods, such as breast MRI, may be advisable for women with dense breast tissue.
- Ethnic or Racial Background—White, non-Hispanic women develop breast cancer more frequently than African-American women. But when African-American women do get breast cancer, their mortality rate is higher. A woman is more likely to develop breast cancer before age 45 if she is of Hispanic, Asian, or Native American origin.
- Family History—Having one first-degree relative (mother, sister, or daughter) who has had breast cancer doubles a woman’s lifetime risk. If two first-degree relatives have a history of breast cancer, a woman’s lifetime risk triples. Most women diagnosed with breast cancer, however, do not have a family history of the disease. This makes screenings for early detection important, regardless of family history.
- Gender—Women are at 100 times greater risk of breast cancer than men.
- Genetics—An estimated 5 to 10 percent of breast cancer cases are related to genetic mutations that run in families. The most common mutations occur in the BRCA1 and BRCA2 genes, but researchers believe that there are other genes that may also affect breast cancer risk.
- History of Benign (Noncancerous) Breast Conditions—Some, but not all, benign breast conditions slightly increase breast cancer risk. This includes such conditions as ductal hyperplasia, fibroadenoma, and sclerosing adenosis.
- History of Radiation Therapy to the Chest—If a patient has had radiation therapy in the past for cancers in the chest area other than breast cancer, her breast cancer risk is slightly increased.
- Personal History—If a woman has been diagnosed with breast cancer one or more times in the past, the likelihood is three to four times higher that she will develop a new cancer, in either the other breast or a different location in the same breast.
- Lifestyle Factors—Certain lifestyle factors may affect a woman’s breast cancer risk, including:
- Alcohol use
- Being overweight or obese, especially after menopause
- Having no children, or having the first child after age 30
- Hormone therapy after menopause with both estrogen and progesterone
- Sedentary lifestyle (little exercise or physical activity)
- Use of oral contraceptives more recently than the last 10 years
This list of risk factors is not all-inclusive. To learn more about breast cancer risk, visit the Learn About Breast Cancer page on the American Cancer Society Website. It is especially important for a woman to keep her primary care provider informed about any breast cancer risk factors in her personal or family history. This will help the provider recommend the best approach to prevention and early detection, such as the appropriate age to begin annual mammograms and whether additional screening methods are advisable.
Screening for Breast Cancer
Screening guidelines for women who are at average risk for breast cancer fall into two age-based categories:
- Women ages 20–39: In this age group, women should perform monthly breast self-exams, reporting any lumps or changes to their primary-care provider immediately. For more information about self-exams, see The National Breast Cancer Foundation’s Breast Self-Exam page.
- Women age 40 and over: Continued monthly breast self-exams, and annual mammograms starting at age 40, are recommended.
Women with factors that increase breast cancer risk and/or dense breast tissue may need additional measures, such as:
- Annual mammograms before 40
- Additional screenings, such as breast MRI, in conjunction with annual mammograms
To review additional useful information, see the Mammography Saves Lives website.