Breast Cancer Basics

What it is

A breast is made up of three main parts: lobules, ducts, and connective tissue. The lobules are the glands that produce milk. The ducts are tubes that carry milk to the nipple. The connective tissue (which consists of fibrous and fatty tissue) surrounds and holds everything together.

Breast cancer is a disease in which cells in the breast grow out of control. There are different kinds of breast cancer. The kind of breast cancer depends on which cells in the breast turn into cancer.

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This diagram of the breast shows the location of the lobules, lobe, duct, areola, nipple, and fat.

Most breast cancers begin in the ducts or lobules. Breast cancer can spread outside the breast through blood vessels and lymph vessels. When breast cancer spreads to other parts of the body, it is said to have metastasized.

Types

The most common kinds of breast cancer are:

• Invasive ductal carcinoma. The cancer cells begin in the ducts and then grow outside the ducts into other parts of the breast tissue. Invasive cancer cells can also spread, or metastasize, to other parts of the body.

• Invasive lobular carcinoma. Cancer cells begin in the lobules and then spread from the lobules to the breast tissues that are close by. These invasive cancer cells can also spread to other parts of the body.

There are several other less common kinds of breast cancer, such as Paget's disease, medullary, mucinous, and inflammatory breast cancer.

Ductal carcinoma in situ (DCIS) is a breast disease that may lead to invasive breast cancer. The cancer cells are only in the lining of the ducts and have not spread to other tissues in the breast.