MONOCLONAL-ANTIBODY 4D3 DETECTS SMALL-INTESTINAL MUCIN ANTIGEN (SIMA)GLYCOPROTEIN IN THE SERUM OF PATIENTS WITH COLORECTAL-CANCER

We have developed a sensitive ELISA using MAb 4D3 for the detection of a novel epitope on Small Intestinal Mucin Antigen (SIMA) and report h ere that SIMA is present in the serum of patients with colorectal canc er. SIMA has been shown to occur in tissue from a high proportion of p atients with colorectal cancer. SIMA derived from serum was similar to tissue-derived SIMA: both eluted in the void volume of a Superose 6 c olumn indicating a molecular weight above 5,000 kDa and they exhibited similar buoyant densities on CsCl gradients. The ELISA was most relia ble after pre-treatment of serum with 0.4 M perchloric acid to remove interfering substances. The upper limit for SIMA in normal serum was s et as the mean plus 2 standard deviations determined from a group of 9 7 healthy control subjects. In a sample of 113 patients with colorecta l cancer, SIMA serum levels were elevated in 15% of patients with Duke s' Stage A, 38% with Stage B, 32% with Stage C and 75% with Stage D co lorectal cancer. SIMA serum levels were compared with those of the wid ely used tumor marker, carcino-embryonic antigen (CEA). The SIMA assay detected a significant number of sera that were not detected by the t est for CEA. We propose that SIMA will prove to be a valuable serologi cal tumor marker, in combination with CEA and other tumor markers, for the detection of colorectal cancer.