BREAST CANCER

Causes

Cancer affects your cells, the basic units of life. Normally, cells grow and divide in an orderly way. But sometimes this growth gets out of control — cells continue dividing even when new cells aren't needed. These extra cells may form a mass of tissue called a tumor.

Tumors may be either noncancerous (benign) or cancerous (malignant). Cells from malignant tumors can invade and damage nearby tissues and organs. They may also travel through your blood stream or lymph system to other parts of your body.

In most cases, it isn't clear what triggers abnormal cell growth in breast tissue. It is known that between 5 percent and 10 percent of breast cancers are inherited. Defects in one of two genes, breast cancer gene 1 (BRCA1) or breast cancer gene 2 (BRCA2), put you at greater risk of developing the disease. In fact, women who have mutations in these genes have a 56 percent to 87 percent lifetime chance of developing breast cancer and a 20 percent to 60 percent chance of developing ovarian cancer. Both men and women can inherit these genes from either parent.

Although the discovery of these genes is important, it's only the first step. Breast cancer is a complex disease that eventually may prove to have a number of causes.