Tumor imaging and pharmacokinetics of Tc-99m labelled monoclonal antibody 170H.82 in patients with colorectal cancer

MAb 170H.82 is an antibody directed against a membrane associated protein expressed on the majority of human adenocarcinomas. Tc-99m-MAb 170H.82 was evaluated as a method of imaging primary and metastatic colorectal cancer, Twenty-three patients were injected intravenously with 1300-1800 MBq (1.6-1.8 mg) of Tc-99m-MAb 170.H82. Planar and SPECT images of the abdomen and pelvis were obtained at 4h and 22h post injection, Twenty-two patients underwent laparotomy and samples of tumor and normal tissue were obtained, MAb 170H.82 correctly identified the primary tumor in 7 of 9 patients. Metastatic colorectal cancer was correctly localized in 7 of 13 sites with biopsy confirmation. Interestingly, four patients with high, rising carcinoembryonic antigen levels exhibited positive MAb 170H.82 scans but metastatic colorectal cancer was not confirmed at laparotomy. Three of these patients subsequently developed recurrent disease proximate to the area of increased radiolabel uptake on their scans, Relatively low tumor:serum (0.2-0.3:1) and tumor:liver (0.5:1) ratios may be responsible for the inability of Tc-99m-MAb 170H.82 to detect metastatic colorectal cancer in some patients. Despite these pharmacokinetic limitations, our study demonstrates that Tc-99m-MAb 17OH.82 may allow detection of occult colorectal cancer deposits prior to their recognition by conventional radiologic means in some patients.