Breast Cancer

The American Cancer Society estimates that about 254,650 new cases of breast cancer were diagnosed in the United States in 2009, and that about 40,170 women died from the disease in the same time period. Breast cancer is the second most common cancer in women, after skin cancers, and second only to lung cancer as the cause of cancer death in women.  More than 2.5 million women in the United States have completed or continue treatment for breast cancer.

Early stage breast cancer, in which the cancer cells have not grown deeper into breast tissue or spread to other organs, is known as carcinoma in situ (CIS).  About 20% of new breast cancers are localized to the duct, and are known as ductal carcinoma in situ (DCIS). Invasive breast cancer, which comprises most cases, occurs when the cancer spreads beyond the layer of cells that first became malignant. Invasive ductal carcinoma, in which the cancer starts in the duct and grows into fatty breast tissue, is the most common type of breast cancer, and accounts for about 80% of invasive breast cancers. About 10% of invasive breast cancers originate in the milk-producing cells within the breast and then spread to other parts of the body. Another 1% to 3% of all breast cancers are inflammatory breast cancer, a cancer in which there is usually no single tumor.

Age and gender are both risk factors for developing breast cancer, with about 66% of cases diagnosed over the age of 55 years. About 5% to 10% of breast cancer cases result from inherited mutations in specific genes. A family or personal history of breast cancer also increases the risk of developing the disease. Women who don't’ have children, have children later in life, or use oral contraceptives have an increased risk for developing breast cancer. Hormone therapy using both estrogen and progesterone increases the risk of developing and dying from breast cancer. Other risk factors include drinking alcohol, being overweight, or obesity.

Surgery is used to treat most breast cancers, either removing all or part of the affected breast.  Radiation may be used after surgery to kill any remaining cancer cells. Chemotherapy may be used prior to surgery to shrink the tumor, after surgery to kill any remaining cancer cells, or as the main therapy for women whose cancer has spread beyond the breast and nearby lymph nodes. Targeted therapies may be used in women whose breast cancers express or overexpress specific proteins. Hormone therapy may be used to treat or reduce the risk of recurrence for breast cancers that express receptors for estrogen and/or progesterone.

Adapted from the American Cancer Society’s “Detailed Guide: Breast Cancer”

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