Breast Cancer Overview

Breast cancer is cancer arising in breast tissue. Cancer is simply a group of abnormal cells that have abnormal growth patterns.
Although breast cancer is primarily a disease of women, almost 1% of breast cancers occur in men. In 2007, it is estimated that 2,030 men in the U.S. will develop invasive breast cancer.
Breast cancer is the most common type of cancer in women with the exception of nonmelanoma skin cancers. It is the second leading cause of death by cancer in women, following only lung cancer.
In 2007, the American Cancer Society estimated that 178,480 new cases of invasive breast cancer would be diagnosed among women in the United States, and that a further 62,030 new cases of in-situ (noninvasive) breast cancer would be diagnosed.
A woman has a lifetime risk of developing invasive breast cancer of about one in eight, or 13%.
Death rates from breast cancer have been gradually declining and continue to decline. These decreases are likely due both to increased awareness and screening and improved treatment methods.

The breasts are made of fat, glands, and connective (fibrous) tissue. The breast has several lobes, which are divided into lobules that end in the milk glands. Tiny ducts run from the many tiny glands, connect together, and end in the nipple.
These ducts are where 80% of breast cancers occur. This condition is called ductal cancer.
Cancer developing in the lobules is termed lobular cancer. About 10-15% of breast cancers are of this type.
Other less common types of breast cancer include inflammatory breast cancer, medullary cancer, phyllodes tumor, angiosarcoma, mucinous (colloid) carcinoma, mixed tumors, and a type of cancer involving the nipple termed Paget's disease.

Precancerous changes, called in situ changes, are common.
In situ is Latin for "in place" or "in site" and means that the changes haven't spread from where they started.
When these in situ changes occur in the ducts, they are called ductal carcinoma in situ (DCIS). DCIS may be identified on routine mammography.
When in-situ changes happen in the lobules, it is called lobular carcinoma in situ (LCIS).

When cancers spread into the surrounding tissues, they are termed infiltrating cancers. Cancers spreading from the ducts into adjacent spaces are termed infiltrating ductal carcinomas. Cancers spreading from the lobules are infiltrating lobular carcinomas.
The most serious cancers are metastatic cancers. Metastasis means that the cancer has spread from the place where it started into other tissues distant from the original tumor site. The most common place for breast cancer to metastasize is into the lymph nodes under the arm or above the collarbone on the same side as the cancer. Other common sites of breast cancer metastasis are the brain, the bones, and the liver.