Detection of colorectal carcinoma by anti-CEA monoclonal antibody (IOR-CEA1) labeled with 99mTc scintigraphy.

Background/Aims: This study shows that a new monoclonal antibody (IOR-CEA1) labeled with technetium-99m has high diagnostic efficacy for colorectal adenocarcinoma. This immunoscintigraphy is helpful in clinical management especially for patients whose serum carcinoembryonic antigen and computed tomography are questionable for recurrent diseases. The study aims to evaluate the efficiency of a new monoclonal antibody (IOR-CEA1) labeled with technetium-99m in the detection of colorectal carcinoma. Methodology: Forty colorectal carcinoma patients were examined. They were divided into 2 groups: Group I (9 patients) with untreated primary tumor; and Group II (31 patients) who were suspected of recurrent or residual diseases from 1) equivocal computed tomography or magnetic resonance imaging, or 2) rising serum carcinoembryonic antigen but normal imaging or clinical findings. One milligram of the antibody labeled with 25mCi of technetium-99m was slowly infused intravenously and images were obtained by nuclear medicine techniques. Sensitivity, specificity, accuracy, positive and negative predictive values were determined. Results: 99m Tc-IOR-CEA1 had 86% sensitivity, 71% specificity, 83% accuracy, 94% positive predictive value and 50% negative predictive value for the detection of colorectal cancer in 42 studies (2 patients had repeated studies). Serum carcinoembryonic antigen had only 33% sensitivity for detection of the primary cancer and 58% sensitivity in detection of recurrent diseases. Carcinoembryonic antigen had 100% positive predictive value but only 31.3% negative predictive value for diagnosis of the recurrence of tumor. Fifty-two percent of the antibody scans provided more information than computed tomography scans -with clinical impact on further management in group II patients. Conclusions: The 99m Tc-IOR-CEA1 scintigraphy is a promising investigative method which is safe and has high accuracy in the detection of recurrent colorectal carcinoma, especially in the patients whose serum carcinoembryonic antigen and computed tomography findings are equivocal for recurrent diseases.