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What is Breast Cancer?


Cancer is a general term that is used to describe a group of more than 100 diseases that cause cells in the body to divide and reproduce abnormally without control.

Normal body cells grow, divide, and die throughout a person's lifetime. After reaching adulthood, the growth of new cells is limited to replacement of worn-out or dying cells or to the repair of injured cells.

Body cells sometimes continue to grow and divide abnormally, beyond the body's need for cell growth. These cells may join together to form a mass of extra tissue known as a tumor. Tumors can be malignant or benign.

A malignant tumor is cancerous. Cells in malignant tumors can penetrate and destroy healthy body tissues. Cancer cells can also break away from tumors and travel, or metastasize, to other parts of the body through the bloodstream or lymph system. In this manner, cancer can spread and form secondary tumors in other parts of the body.

A benign tumor is an abnormal growth that is not cancerous and does not spread to other sites in the body. Benign tumors can usually be removed and in most cases do not recur. In almost all instances, benign tumors are not life threatening.

Breast Cancer

Graphic of breast cancer tumorBreast cancer refers to a malignant tumor that has developed from breast cells. Most cancers are classified according to the part of the body in which the cancer began, even if the cancer has metastasized to other parts of the body; therefore, if a cancer that develops in the breast spreads to the lung or another body part, it is still referred to as breast cancer or metastatic breast cancer.

Graphic of infiltrating lobular carcinomaThere are two general categories of breast cancer: noninvasive, where the cancer cells are confined to the ducts (milk passages); and invasive, where the cancer cells have broken through the duct into the surrounding fatty and connective tissues. Within these categories, there are a number of unique cancer types, affecting different components of the breast.

For more detailed information about the various forms of breast cancer, please see Types of Breast Cancer.

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