What Causes Breast Cancer Everyday Health MenuNewslettersSearch Breast Cancer What Causes Breast Cancer By Cathy CassataMedically Reviewed by Thomas Urban Marron, MD, PhDReviewed: February 9, 2022Medically Reviewed While the exact cause of breast cancer isn't known, we do know that the disease occurs when some breast cells begin growing abnormally. These cells divide more rapidly than healthy cells and then start to accumulate, forming a lump or mass. These cancer cells can spread (metastasize) throughout the breast and into lymph nodes or to other parts of your body. Most of the time, breast cancer begins with cells in the milk-producing ducts. But it can also begin in the glandular tissue called lobules, or in other cells within the breast. Breast Cancer Risk Factors While several lifestyle-related, environmental, and hormonal factors may increase your risk of developing breast cancer, none of these factors guarantee you'll develop the disease. Moreover, many women who develop the disease have no known risk factors. Certain traits, however, are known to increase the risk of breast cancer, such as obesity, personal or family history of breast cancer, and genetic mutations. While some people who get breast cancer don't have any of the following risk factors, these traits increase your risk of developing breast cancer:Being a womanObesityOlder agePersonal history of breast cancer in one breast (increases your risk of getting it in the other breast)Family history of breast cancer in close relatives such as your mother, sister, or daughter - especially if they developed the disease at a young ageInherited genetic mutations, such as BRCA1 and BRCA2Radiation exposure to your chest as a child or young adultStarting your menstrual cycle before the age of 12Beginning menopause at an older ageGiving birth for the first time after the age of 35Never being pregnantTaking hormone therapy that combines estrogen and progesteroneDrinking alcohol Inherited Breast Cancer The majority of breast cancers are not inherited. In fact, only 5 to 10 percent of breast cancers are linked to genetic mutations passed down through generations. The most common gene mutations linked to breast cancer are BRCA1 and BRCA2. Both of these mutations also increase the risk of other cancers throughout a woman's lifetime, particularly ovarian cancer. In normal cells, the BRCA1 and BRCA2 genes help prevent cancer by making proteins that keep the cells from growing abnormally. If these genes are mutated, the cancer-prevention response will not work properly. For some women with the BRCA1 mutation, the lifetime risk of breast cancer is as high as 80 percent. On average, however, this risk is more like 55 to 65 percent. For women with the BRCA2 mutation, the lifetime risk of breast cancer is around 45 percent. Breast cancers linked to these mutations occur more often in younger women. Cancer affecting both breasts is also more common than in cases not linked to these mutations. While the BRCA1 and BRCA2 mutations may affect anyone, they are more common in Jewish people of Eastern European origin than in other racial and ethnic groups in the United States. Men can also carry these mutations, and if they do they are at increased risk for breast and other cancers, such as prostate cancer. Genetic Testing Genetic testing may be an option if you have a family history of breast cancer or other cancers. Through a blood or saliva test, scientists can identify specific inherited mutations in BRCA or other genes. Talk with your doctor about whether genetic testing is a good option for you. Your doctor can also recommend a genetic counselor who can discuss your testing options with you in detail. Check with your insurance company to see if BRCA1 and BRCA2 mutation testing is covered under your plan. Genetic counseling and testing for people at high risk is a covered preventive service under the Affordable Care Act (ACA). 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Editorial Sources and Fact-Checking BRCA1 and BRCA2: Cancer Risk and Genetic Testing; National Cancer InstituteBreast Cancer; Mayo ClinicBreast Cancer; American Cancer SocietyShow Less The Latest in Breast Cancer How to Avoid Pink Ribbon Pitfalls During Breast Cancer Awareness MonthBefore you donate to a breast cancer organization this month, make sure you know where your money’s going. By Leona VaughnSeptember 30, 2022 Cancer Me and My Solo RaftBy Denise SchipaniSeptember 13, 2022 Targeted Therapies for Metastatic Breast Cancer— Here' s What You Should KnowThe latest treatments and therapy approaches for metastatic breast cancer are helping patients live longer and offering new hope.By Cheryl Platzman WeinstockSeptember 7, 2022 Struggling With Insomnia During Breast Cancer Treatment Here s How to DealBreast cancer treatment can bring about many sleepless nights. 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