Role of B72.3 iodine 125-labeled monoclonal antibody in colorectal cancer detection by radioimmunoguided surgery

Background. Radioimmunoguided surgery (RIGS) by means of radiolabeled monoclonal antibodies and a probe has been reported to be useful in recognizing subclinical tumor deposits during operation. Aim of this study was to understand the limits of this technique and to access the potential diagnostic use of RIGS in colorectal cancer surgery. Methods. Monoclonal antibody B72.3 reacting with TAG 72 antigen, labeled with iodine, 125, was injected in 32 patients with primary tumors and in 22 patients with recurrent colorectal cancer. One hundred thirty-three suspected tumor sites were evaluated during operation by means of probe and resected with immunohistochemistry as control. Results. Primary tumor sites were localized by RIGS in 60% of cases, and recurrent sites were localized in 82% of cases. There was a significant correlation both for primary (p<0.001) and recurrent (p<0.001) tumor sites between intraoperative RIGS findings and TAG 72 tumor antigen expression. Results obtained with the probe were instrumental in modifying the surgical approach in six (27%) of 22 patients with recurrences, allowing the removal of tumor masses that would otherwise have been overlooked. Conclusions. The results of RIGS seems to be encouraging in terms of clinical use. The potential high diagnostic resolution appears to improve surgical ablation of colorectal cancer, especially in patients with recurrent cancer or suspected recurrent tumors who have negative results for intraabdominal disease by all other roentgenographic criteria with rising carcinoembryonic antigen or TAG 72 antigen levels