Improved specificity of the CA 125 enzyme immunoassay for ovarian carcinomas by use of the ratio of CA 125 to carcinoembryonic antigen.

We found that ovarian cyst fluids contained carcinoembryonic antigen (CEA) and CA 19-9 and CA 125 tumor markers. However, only the ratio of CA 125 to CEA concentrations provided sufficient specificity to differentiate serous from mucinous cysts. For CEA measurement, our results suggested the use of a monoclonal CEA kit. When CEA was determined with a Hybritech monoclonal CEA kit, all ratios in mucinous ovarian cysts were less than 10 and most of the ratios were greater than 1000 in serous ovarian cysts. We also found that the ratio of CA 125 to CEA in serum could be used to differentiate ovarian from nonovarian malignant diseases when both sera contain increased CA 125 concentrations. The nonovarian malignancies consisted of colorectal, breast, lung, and pancreatic carcinomas. The mean ratio for serum from patients with nonovarian cancers was 0.94 (n = 19); for ovarian-cancer patients (n = 45), 916. Therefore, determining this ratio will greatly improve the specificity of the CA 125 test for ovarian cancer.