CA 15.3 molecule is a mucin, being a product of the MUC1 gene. Other names for this mucin include polymorphic epithelial mucin (PEM), epithelial membrane antigen (EMA) or episalin. The MUC1 antigen is a transmembrane Glyco-protein containing a large extra cellular domain, a hydrophobic membrane -spanning domain of 31 amino acids and a cytoplasmic domain of 69. amino acids. CA 15.3 is a highly polymorphic glycoprotein expressed at the apical surface of normal epithelial cells.
The most common type of breast cancer begins in the lining of the ducts and is called ductal carcinoma. Another type, called lobular carcinoma, arises in the lobules. When breast cancer spread outside the breast, cancer cells are often founded in lymph nodes under the arm. If the cancer has reached these nodes, it may mean that cancer cells have spread to other parts of the body -other lymph nodes and other organs, such as bones , liver, or lungs-via the lymphatic system or the blood stream. Cancer that spreads is the same disease and has the same name as the original (primary) cancer. When breast cancer spreads, it is called metastatic breast cancer, even though the secondary tumor is in another organ. Doctors sometimes call "distant" disease.
The risk of breast cancer increases gradually as a woman gets older. This disease is uncommon in women under the age of 35. All women age 40 and older are at risk for breast cancer. However, most breast cancer occur in women over the age of 50, and the risk is especially high for women over age 60. The risk factors of breast cancer are personal history of breast cancer, genetic alternations, family history, certain breast changes, breast density, radiation therapy, and late child bearing. Also at a somewhat increased for developing breast cancer are women who started menstruating at an early age (before age 12), experienced menopause late (after age 55), never had children, or took hormone replacement therapy or birth control pills for long period of the time. Each of these factors increases the amount of time a woman's body is exposed to estrogen. The longer this exposure, the more likely she is to develop breast cancer.