Breast Cancer

Source: MedlinePlus Health Topics, U.S. National Library of Medicine

Last synced 8/9/2026Status: primary verified

What is breast cancer? Breast cancer is a cancer that starts in breast tissue. It happens when cells in the breast change and grow out of control. New cells grow even when you don't need them, and old cells don't die when they should. These extra cells can form a mass called a tumor. Sometimes the cancer does not spread any further. This is called "in situ." If the cancer spreads outside the breast, the cancer is called "invasive." It may just spread to nearby tissues and lymph nodes. Or the cancer may metastasize (spread to other parts of the body) through the lymph system or the blood. Breast cancer is the second most common type of cancer in women in the United States. Rarely, it can also affect men . What are the types of breast cancer? There are different types of breast cancer. The types are based on which breast cells turn into cancer. The types include: Ductal carcinoma , which begins in the cells of the ducts. This is the most common type. Lobular carcinoma , which begins in the lobules. It is more often found in both breasts than other types of breast cancer. Inflammatory breast cancer , in which cancer cells block lymph vessels in the skin of the breast. The breast becomes warm, red, and swollen. This is a rare type. Paget's disease of the breast , which is a cancer involving the skin of the nipple. It usually also affects the darker skin around the nipple. It is also rare. What causes breast cancer? Breast cancer happens when there are changes in the genetic material (DNA). Often, the exact cause of these genetic changes is unknown. But sometimes these genetic changes are inherited, meaning that you are born with them. Breast cancer that is caused by inherited genetic changes is called hereditary breast cancer. There are also certain genetic changes that can raise your risk of breast cancer, including changes in the BRCA1 and BRCA2 genes. These two changes also raise your risk of ovarian and other cancers. Besides genetics, your lifestyle and the environ

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This information is for general education and is not medical advice. Always talk to a licensed U.S. clinician about your situation, medications, or treatment decisions.