Breast cancer is a major killer of women. Approximately 179,000 women were diagnosed with breast cancer in the U.S. in 1998 and 43,500 women died of this disease . Breast cancer is a disease in which there is a loss of control of the proliferation of the epithelial (glandular) cells. The breast is structurally organized as shown in Figure 5.1. It is composed of several lobes, each of which drains into a major duct and these converge at the nipple. Each lobe contains lobules composed of the glandular tissue which, in lactation, delivers milk to the ducts. Breast cancer occurs in the terminal ductal lobular unit, usually within the ductules. As long as the cancer cells remain within the duct (ductal carcinoma in situ or DCIS) the probability of a cure is very high. Once the cancer becomes invasive, the cells have the potential to migrate away from their site of origin. Commonly, they enter the lymphatic system and cancer cells may lodge in the axillary lymph nodes in the armpit or spread further (metastasize) to more distant sites in the body such as the liver or brain. Most frequently, it is metastatic cancer which causes death from breast cancer.
The causes of breast cancer are largely still unknown, although in the last few years, two genes, which in a mutated form carry a high risk of breast cancer, have been identified. This likely only accounts for about 4% of breast cancer incidence and most breast cancer is of unknown etiology (cause).
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