Comparative evaluation of serum CA 195 and carcinoembryonic antigen in metastatic carcinoma

Carcinoembryonic antigen (CEA) is a well-described human tumor-associated antigen most useful clinically in colon cancer. However, the clinical usefulness of CEA is limited by the marker's overall poor specificity and low sensitivity in patients with minimal disease. CA 195 is a recently discovered human tumor-associated glycoprotein that can be measured in serum using an immunoradiometric assay. CA 195 is expressed on the membrane of human colon cancer cells and shares an epitope with the Lewis A blood group antigens. The authors initiated a study to compare the clinical utility of serum CA 195 with CEA in patients with advanced cancer. A control population was studied to assess the effects of age, gender, alcohol, and tobacco on the measured levels of serum CA 195.

Using a solid-phase two-site immunoradiometric assay, serum CA 195 and CEA levels were measured in 71 control subjects and 167 patients with a prior diagnosis of cancer. The tumor histologic types included breast cancer, 49 patients; colon cancer, 38; prostate cancer, 24; lung cancer, 22; gastrointestinal noncolon cancer, 7; and miscellaneous, 27. Among patients with a history of cancer, 124 (74%) had active metastatic disease, and 43 (26%) were without evidence of active disease. The control population was composed of subjects without a history of malignancy. Clinical data collected from them included age, gender, smoking history, and alcohol consumption.

In this laboratory, the normal ranges established for CA 195 and CEA in the control group were: 0.0-8.3 U/ml and 0.2-4.2 ng/ml, respectively. In the control subjects, the serum CA 195 level, unlike that of CEA, was not affected by age, gender, alcohol consumption, or tobacco use. In the study population, CA 195 had either equivalent or inferior specificity and sensitivity to CEA in all tumor types. A determination of the additive specificity and sensitivity of CA 195 and CEA did not significantly improve its clinical utility compared with CEA alone. However, CA 195 was significantly elevated in three patients with a prior history of colon cancer thought to be without evidence of active disease. Because all three of these patients had a relapse within the next 1-15 months, CA 195 might identify early relapses of colon cancer in some patients.

Based on these results, it was concluded that CA 195 is not superior to CEA as an indicator of disease activity in advanced colon cancer or other solid tumors. However, studies utilizing CA 195 in the detection of early relapses of colon cancer may be warranted. A review of the English literature revealed that CA 195 might be a useful marker in pancreatic cancer.