Serum CA 12-5 concentrations and CA 12-5/CEA ratios in patients with epithelial ovarian cancer

In attempts to increase the specificity of the CA 12-5 test the ratio of CA 12-5 and CEA concentrations has been determined in 155 cancer patients, all of whom had an increased serum CA 12-5. The patients included 47 with epithelial ovarian cancer, 38 with colorectal cancer, 24 with cervical cancer, 20 with lung cancer, 17 with gastric cancer, and 9 with pancreatic cancer. The CA 12-5/CEA ratio in serum of patients with ovarian cancer ranged from 30 to 920 (mean 251), whereas in other types of cancer the highest ratio was 240 and the mean was 13. All 47 patients with ovarian cancer, but only 7 of the 108 patients with other types of cancer, showed a CA 12-5/CEA ratio greater than 25. About 10% of the patients with gastric or colorectal cancer but none of those with other types of cancer showed an increased ratio. As the predictive value of a CA 12-5/CEA ratio of less than 25 excluding ovarian cancer is 100%, we recommend measuring the CEA concentration in all those with increased CA 12-5 and calculation of the CA 12-5/CEA ratio.