Evaluation of colorectal cancer-associated mucin CA M43 assay in serum.

The technical performance of a newly developed assay for CA M43, a serum marker for colorectal cancer, was evaluated and its preliminary clinical potential assessed. The heterologous double-determinant enzyme immunoassay for the detection of the tumor-associated mucin CA M43 utilizes two monoclonal antibodies (CT 43 and CT 66) selected for their binding capacity to two distinct epitopes present on mucins in the sera of patients with colorectal cancer. CT 66 recognizes both Lewis(a) and sialylated Lewis(a) antigen; CT 43 is directed toward a mucin epitope of an as-yet uncharacterized structure. Precision experiments revealed interassay CVs of 11.8%, 5.9%, and 4.9% at 9.3, 11.9, and 78.9 units/mL, respectively; intraassay precision was 2.0% at 95.1 units/mL. The upper normal value was set at 7.5 units/mL, which included 99% of the values found in healthy controls. In colorectal cancer patients, CA M43 showed a positivity rate equivalent to that of carcinoembryonic antigen (CEA) and superior to that of CA 19.9, with only one CA 19.9-positive serum being negative for CA M43. Interestingly, CA M43 appeared to be complementary to CEA, with CA M43 and CEA together reaching 87% positivity in metastatic disease.