Serum levels of cancer‐associated antigen 195, a circulating marker for colon cancer, and its relationship to carcinoembryonic antigen

Abstract

AbstractCA‐195 is a circulating cancer‐associated antigen defined by its reactivity with monoclonal antibody CC3C 195. The epitope with which this antibody reacts has previously been shown to be the Lewis A blood group antigen and its sialylated derivative.By using CC3C 195 as both capture and tracer antibody, serum levels of CA‐195 were measured with an immunoradiometric assay. CA‐195 was found to be elevated in the sera of 36 of 68 advanced colon cancer patients, 12 of 26 advanced liver cancer patients, 9 of 30 advanced breast cancer patients, and 4 of 19 advanced lung cancer patients. This is in contrast to healthy individuals, in which only 11 of 203 had elevated CA‐195, and to benign colon disease patients, which had 10 of 76 elevated. Benign breast disease patients, benign liver disease patients, and benign lung disease patients had 5 of 30, 6 of 25, and 2 of 30 sera with elevated CA‐195 levels, respectively. This elevation of serum CA‐195 was statistically significant in colon cancer patients compared to benign colon patients (P<.0001) or healthy individuals (P<.0001), as well as in liver cancer patients compared to benign liver patients (P < .025). Elevations in other conditions studied were not statistically significant. A separate panel of sera from staged, pretreatment colon cancer patients was also tested, and elevated CA‐195 was found in 6 of 17, 17 of 54, 10 of 18, and 12 of 17 patients which were staged Dukes A, 8, C, and D, respectively. Dukes C and/or D patients were significantly elevated compared to Dukes A and/or 6 (P<.0035), and all stages were significantly elevated compared to sera from healthy individuals (P<.0001). This indicates that the incidence of CA‐195 elevation increases as the disease progresses and suggests that CA‐195 may be a useful marker at all stages. Anticarcinoembryonic antigen (CEA) and anti CA‐195‐coated beads were used to immunodeplete specimens; CA‐195 epitopes were found to be present on the same molecular structure as CEA epitopes in tumors but not in patients' sera. This confirms the nature of CA‐195 as a separate cancer marker in patients' sera and suggests that cleavage of CA‐195 and CEA epitopes from a larger precursor moiety occurs prior to secretion into the serum.