Comparative analysis of cancer-associated antigen CA-195, CA 19-9 and carcinoembryonic antigen in diagnosis, follow-up and monitoring of response to chemotherapy in patients with gastrointestinal cancer.

To establish further the clinical significance of the CA-195 tandem immunoradiometric assay in gastro-intestinal malignancies, the sera of a total of 222 subjects have been analysed and compared with assays of the "classical gastrointestinal tumour markers", CA19-9 and carcinoembryonic antigen (CEA). CA-195 elevations above normal (greater than 10 U/ml) were noted in 51/72 (70.8%) colorectal, 15/15 (100%) pancreatic, and in 6/12 (50%) gastric cancer patients. Whereas CA19-9 was increased (greater than 37 U/ml) in 65%, 93%, and 42% of cases, only 54% colorectal, 45% pancreatic, and 42% gastric cancer patients had pathologically elevated serum CEA levels (greater than 5 ng/ml). No abnormal increase of both CA-195 and CA19-9 was found in healthy volunteers, whereas 3/20 (smoking) individuals had CEA levels slightly above normal. With a 29% false-positive rate noted among 103 patients with benign gastrointestinal disorders, the specificity of CA-195 was superior to that of CA19-9 (58%) and comparable with that of CEA (31%). A significant correlation between CA-195 levels and the clinical/pathological stage of disease was noted in colorectal (P less than 0.01) and pancreatic cancer patients (P less than 0.007). Preliminary results of serial measurements of CA-195 in colorectal cancer suggest that this new marker protein, which has no cross-reactivity with CEA, may be useful as a non-invasive test for postoperative surveillance of patients to detect disease recurrence, and serve to complement (though certainly not replace) standard clinical measurements of response to chemotherapy.