Radioimmunoscintigraphy of colon cancer with iodine-131-labeled B72.3 monoclonal antibody.

The monoclonal antibody B72.3 is a murine IgG1 that is reactive with a wide range of carcinomas while demonstrating little or no reactivity to normal adult tissues. We have shown (27) quantitative analyses demonstrating selective targeting of [131I]B72.3 IgG to metastatic colorectal cancer. We have also shown (28) that (a) B72.3 localization in metastases correlated with the percentage of tumor cells in the biopsy specimen; (b) B72.3 could localize in carcinomas of various degrees of differentiation with best localization in well-differentiated tumors and (c) [131I]B72.3 could penetrate tumor masses, as determined by autoradiographic studies. We report here the various parameters effecting radioimmunoscintigraphy with [131I]B72.3 IgG. Sixteen of 35 patients with colorectal carcinoma had positive scans (without blood-pool subtraction). High circulating TAG-72 antigen levels correlated with positive scans. No dose dependent differences were seen in biodistribution or tumor imaging. The plasma clearance and urinary excretion of [131I]B72.3 and [125I]BL-3 (nonspecific control) were not significantly different. No toxicity was noted. Approximately one-half of patients developed human anti-mouse immune response.