Cancer-associated serum antigen (CASA) and ovarian serum antigen (OSA): Two new tumor marker kits for detecting carcinoma-associated mucins

We have developed two sandwich enzyme immunoassay kits for the measurement of carcinoma-associated mucins in epithelial carcinomas (Cancer-Associated Serum Antigen, CASA) and in ovarian carcinoma (Ovarian Serum Antigen, OSA). The technical performance of the kits and a clinical study of the two markers in breast cancer is described. Both assays had low inter and intra-assay coefficients of variation and did not have sample addition drift. Both CASA and OSA gave excellent sample dilution linearity. Because of sequential rather than simultaneous incubations of test sera then second Mab, there is no high dose hook effect. Using arbitrary cut-off levels of 4u/mL (CASA) and 3u/mL (OSA) 2% of 98 normal females were positive compared to 76.5% (CASA) and 70.3% (OSA) of patients with active advanced breast carcinoma (n = 64). These findings were similar to those previously observed in ovarian cancer where OSA levels were increased in 82% of subjects compared to 76% by the CASA assay. A comparison of Mammary serum Antigen (MSA) and CASA levels in breast cancer patients showed both markers to be within normal limits in 10/11 patients with no evidence of disease. CASA levels were increased in 77.5% (21/27) of patients with active Stage III/IV breast carcinoma compared to 81% (22/27) in the MSA test. These studies demonstrate that both CASA and OSA levels are elevated in the majority of patients with advanced breast cancer and that these tests may be useful in monitoring the disease process