The following information is taken from the booklet What You Need to Know About Breast Cancer , published by the National Cancer Institute. The NCI is the U.S. Government's main agency for cancer research and information about cancer. What You Need to Know About Breast Cancer Breast cancer is the most common type of cancer among women in the United States.
Cancer is a group of diseases.
It occurs when cells become abnormal and divide without control or order. Every organ in the body is made up of various kinds of cells. Cells normally divide in an orderly way to produce more cells only when they are needed. This process helps keep the body healthy. If cells divide when new cells are not needed, they form too much tissue.