Overview of Breast Cancer

Breast cancer is malignant abnormal cell growth in the breast. Breast cancer is not one disease, and the condition can be classified into four major subtypes according to two factors: hormone receptor (HR) status and tumor cell activity around a certain gene (called the HER2 gene). These factors affect how the tumor(s) respond(s) to treatment.

Breast cancer cells may spread to other areas of the body (called metastasis). Fibrocystic changes in the breast (e.g., formation of cysts, scar tissue) may cause benign (i.e., noncancerous) lumps in breast tissue. It is important for women to become familiar with their breasts and report changes (e.g., lump, nipple discharge, asymmetry) to their health care provider.

Incidence & Prevalence of Breast Cancer

In women, breast cancer is the second most common type of cancer and the second leading cause of cancer-related deaths. One in eight women in the United States (12 percent) will develop breast cancer during her lifetime. Breast cancer also occurs in men.

According to the American Cancer Society (ACS), approximately 231,840 new cases of invasive breast cancer are diagnosed each year in the United States, and the disease causes about 40,290 deaths annually.

The incidence of breast cancer rises after age 40. The highest incidence (approximately 80 percent of invasive cases) occurs in women over age 50.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 14 Aug 1999

Last Modified: 02 Sep 2015