A comparison of the clinical usefulness of CA 19-9 and CA 50 in the diagnosis and monitoring of gastrointestinal cancers.

We compared serum levels of CA 19-9 and CA 50 in 108 patients with malignant neoplasms of the stomach, pancreas, liver, and colon with the serum levels in 60 patients with benign gastrointestinal diseases, and 10 healthy subjects. Increased serum levels of CA 19-9 and CA 50 were found in 51.8 and 62% of the cancer patients, respectively. The results of CA 19-9 and CA 50 assays in the nonneoplastic group showed less specificity. False positive results were noted in 11.7% of CA 19-9 tests and in 31.6% of CA 50 tests. We concluded that in gastrointestinal cancer, the CA 19-9 test should be performed initially. CA 50 determination can be useful, but the lower specificity of the test should be taken into consideration. CA 50 should be recommended only for postoperative monitoring, especially in patients with normal CA 19-9 serum levels.