Breast Cancer; Overview.

Breast cancer is the most common cancer in women, other than skin cancer, and the second deadliest cancer in U.S. women; lung cancer is the deadliest. Approximately 182,460 cases of invasive breast cancer will be diagnosed in 2008, according to the American Cancer Society (ACS). Though an estimated 40,480 women will die from breast cancer, there are about 2.5 million breast cancer survivors in the U.S., according to the ACS.

Fortunately, the number of deaths caused by breast cancer has declined significantly in recent years, with the largest decreases in younger women--both Caucasian and African American. These decreases are probably the result of earlier detection and improved treatment.

The National Cancer Institute found a very significant drop in the rate of hormone-dependent breast cancers among women, the most common breast cancer, in 2003. In a study published in late 2006, researchers speculated that the drop was directly related to the fact that millions of women stopped taking hormone therapy in 2002 after the results of a major government study found the treatment slightly increased a woman's risk for breast cancer, heart disease and stroke. The researchers suggested that stopping the treatment prevented very tiny cancers from growing into tumors large enough to be identified by mammogram or touch because they didn't have the additional estrogen required to fuel their growth.

Breast cancer is a disease in which malignant (cancerous) cells are found in breast tissues. Each breast has 15 to 20 sections called lobes, which have many smaller sections called lobules. The lobes and lobules are connected by thin tubes called ducts. The different kinds of breast cancer that involve the lobes, lobules and/or ducts are:

Ductal carcinoma in Situ (DCIS). Also known as intraductal carcinoma or non-invasive breast cancer, DCIS is confined to the ducts and has not invaded surrounding tissue. As the use of screening mammography has increased in the United States, the frequency of DCIS diagnosis has increased significantly. It is the most rapidly growing subgroup of breast cancer; one out of five cases of breast cancer is DCIS.

Invasive ductal cancer. Also called infiltrating ductal carcinoma, this type of breast cancer is the most common of all breast cancers. It makes up about 80 percent of all newly diagnosed cases. It is found in the cells of the ducts and is usually a hard lump.

Invasive lobular carcinoma. This form of breast cancer occurs at the ends of the ducts or in the lobules and accounts for 10 percent of invasive breast cancers.

Less common types of breast cancer:

Mucinous carcinoma (colloid carcinoma). A rare type of invasive breast cancer, mucinous carcinoma is formed by mucin-producing cancer cells. Prognosis for this type of invasive breast cancer is generally better than for other more common types.

Medullary carcinoma. This type of breast cancer accounts for five percent of all breast cancers and involves a distinct boundary between tumor tissue and normal tissue. It also differs from other forms of invasive ductal cancers in that it contains large cancer cells and immune system cells throughout the tumor. The prognosis for this type of cancer is generally better than for other invasive forms.

Tubular carcinoma. Tubular carcinoma is characterized by tubular structures ringed with a single layer of cells. Only two percent of all breast cancers fall into this category. The prognosis is usually good.

Invasive Paget's disease. A rare breast cancer in the ducts beneath the nipple accounting for only one percent of cases, invasive Paget's disease starts with an itchy, eczema-like rash around the nipple. Paget's disease can be associated with a noninvasive or invasive underlying mass. For noninvasive cases, it is believed that the cells have migrated from the ducts of the nipple to the nipple's epidermis, though this is still under study.

Inflammatory carcinoma. This aggressive type of breast cancer accounts for one to three percent of all cases. Skin over the breast appears acutely inflamed and swollen because skin lymph vessels are blocked by cancer.

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Keywords: breast cancer, lobes, lobules, ducts, ductal carcinoma in situ, ductal carcinoma, dcis, invasive