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What is Breast Cancer?

What is Breast Cancer?

Cancer is a group of diseases in which cells in the body grow, change, and multiply out of control. Usually, cancer is named after the body part in which it originated; thus, breast cancer refers to the erratic growth and proliferation of cells that originate in the breast tissue. A group of rapidly dividing cells may form a lump or mass of extra tissue. These masses are called tumors. Tumors can either be cancerous (malignant) or non-cancerous (benign). Malignant tumors penetrate and destroy healthy body tissues. A group of cells within a tumor may also break away and spread to other parts of the body. Cells that spread from one region of the body into another are called metastases.

The term breast cancer refers to a malignant tumor that has developed from cells in the breast. The breast is composed of two main types of tissues: glandular tissues and stromal (supporting) tissues. Glandular tissues house the milk-producing glands (lobules) and the ducts (the milk passages) while stromal tissues include fatty and fibrous connective tissues of the breast. The breast is also made up of lymphatic tissue-immune system tissue that removes cellular fluids and waste.

There are several types of tumors that may develop within different areas of the breast. Most tumors are the result of benign (non-cancerous) changes within the breast. For example, fibrocystic change is a non-cancerous condition in which women develop cysts (accumulated packets of fluid), fibrosis (formation of scar-like connective tissue), lumpiness, areas of thickening, tenderness, or breast pain.

The American Cancer Society estimates that each year over 178,000 American women and 2,000 American men will be diagnosed with breast cancer. Breast cancer is the leading cause of death among women between 40 and 55 years of age and is the second overall cause of death among women (exceeded only by lung cancer). Fortunately, the mortality rate from breast cancer has decreased in recent years with an increased emphasis on early detection and more effective treatments.

The remainder of this article outlines several forms of breast cancer that may be found in women. Click here to learn more about breast cancer in men.

Non-Invasive Breast Cancer Invasive Breast Cancer
Cancer cells that are confined to the ducts and do not invade surrounding fatty and connective tissues of the breast.  Ductal carcinoma in situ (DCIS) is the most common form of non-invasive breast cancer (90%).  Lobular carcinoma in situ (LCIS) is less common and considered a marker for increased breast cancer risk. Cancer cells that break through the duct and lobular wall and invade the surrounding fatty and connective tissues of the breast.  Cancer can be invasive without being metastatic (spreading) to the lymph nodes or other organs.

Common Forms of Breast Cancer

Lobular carcinoma in situ (LCIS, lobular neoplasia): The term, "in situ," refers to cancer that has not spread past the area where it initially developed. LCIS is a sharp increase in the number of cells within the milk glands (lobules) of the breast. Many physicians do not classify LCIS as breast cancer and often encounter LCIS by chance on breast biopsy while investigating an area of concern. LCIS patients are closely monitored every four months with physician performed clinical breast exams in addition to receiving yearly mammography. Other preventive options may also be available for patients with LCIS, including tamoxifen orprophylactic mastectomy (preventive breast removal). Click here to learn more about LCIS.

Ductal carcinoma in situ (DCIS):DCIS, the most common type of non-invasive breast cancer, is confined to the ducts of the breast. DCIS is often first detected on mammogram as microcalcifications (tiny calcium deposits). With early detection, the five-year survival rate for DCIS is nearly 100%, provided that the cancer has not spread past the milk ducts to the fatty breast tissue or any other regions of the body. There are several different types of DCIS. For example, ductal comedocarcinoma refers to DCIS with necrosis (areas of dead or degenerating cancer cells).Click here to learn more about DCIS.

Infiltrating lobular carcinoma (ILC): ILC is also known as invasive lobular carcinoma. ILC begins in the milk glands (lobules) of the breast, but often spreads (metastatizes) to other regions of the body. ILC accounts for 10% to 15% of breast cancers.

Infiltrating ductal carcinoma (IDC): IDC is also known as invasive ductal carcinoma. IDC begins in the milk ducts of the breast and penetrates the wall of the duct, invading the fatty tissue of the breast and possibly other regions of the body. IDC is the most common type of breast cancer, accounting for 80% of breast cancer diagnoses.

Less Common Forms of Breast Cancer

Medullary carcinoma: Medullary carcinoma is an invasive breast cancer that forms a distinct boundary between tumor tissue and normal tissue. Only 5% of breast cancers are medullary carcinoma.

Mucinous carcinoma: Also called colloid carcinoma, mucinous carcinoma is a rare breast cancer formed by the mucus-producing cancer cells. Women with mucinous carcinoma generally have a better prognosis (expected outcome) than women with more common types of invasive carcinoma.

Tubular carcinoma: Tubular carcinomas are a special type of infiltrating (invasive) breast carcinoma. Women with tubular carcinoma generally have a better prognosis (expected outcome) than women with more common types of invasive carcinoma. Tubular carcinomas account for around 2% of breast cancer diagnoses.

Inflammatory breast cancer: Inflammatory breast cancer is the appearance of inflamed breasts (red and warm) with dimples and/or thick ridges caused by cancer cells blocking lymph vessels or channels in the skin over the breast. Though inflammatory breast cancer is rare (accounting for only 1% of breast cancers), it is extremely fast-growing.Click here to learn more about inflammatory breast cancer.

Paget’s disease of the nipple: A rare form of breast cancer that begins in the milk ducts and spreads to the skin of the nipple and areola, Paget’s disease of the nipple only accounts for about 1% of breast cancers. The breast skin may appear crusted, red, or oozing in women suffering from this breast cancer. A woman’s prognosis may be better if nipple changes are the only sign of the breast disease and no lump is felt. Click here to learn more about Paget's disease of the nipple.

Phylloides tumor: Phylloides tumors (also spelled "phyllodes") are can be either benign (non-cancerous) or malignant (cancerous). Phylloides tumors develop in the connective tissues of the breast and may be treated by surgical removal. Phylloides tumors are very rare; less than 10 women die of this type of breast cancer each year in the United States. Click here to learn more about benign phylloides tumors.

Additional Resources and References

Updated: June 11, 2008