CA125 also known as mucin 16, is a member of the mucin family glycoproteins. CA125 is a component of the ocular surface (including the cornea and conjunctiva), the respiratory tract and the female reproductive tract epithelia. Since CA125 is highly glycosylated it creates a hydrophilic environment that acts as a lubricating barrier against foreign particles and infectious agents on the apical membrane of epithelial cells.CA125 reacts with both normal tissues and neoplasms of fallopian tube, endometrium, endocervix and mesothelioma. It does not react with colon cancer. Normal tissues such as breast, liver, skin, kidney and spleen are also negative. Studies have shown that CA125 reacts with approximately 80% of epithelial ovarian neoplasms of serous, endometrioid, clear cell and undifferentiated types. No reactivity has been shown for mucinous ovarian tumors or in germ cell or hematopoietic tumors. This antibody is a useful aid for classification of a variety of tumors, such as some adenocarcinomas of the colon, breast carcinomas, malignant mesothelioma, uterine adenomatoid tumor, lung bronchoalveolar carcinoma, and ovarian endometrioid and serous carcinomas.