CA 125 antibody recognizes an epitope on a molecule called Cancer Antigen 125 (CA 125). Studies have shown that CA 125 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. CA 125 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.