TUMOR IMAGING AND PHARMACOKINETICS OF TC-99M LABELED MONOCLONAL-ANTIBODY 170H.82 IN PATIENTS WITH COLORECTAL-CANCER

MAb 170H.82 is an antibody directed against a membrane associated prot ein expressed on the majority of human adenocarcinomas. Tc-99m-MAb 170 H.82 was evaluated as a method of imaging primary and metastatic color ectal cancer, Twenty-three patients were injected intravenously with 1 300-1800 MBq (1.6-1.8 mg) of Tc-99m-MAb 170.H82. Planar and SPECT imag es of the abdomen and pelvis were obtained at 4h and 22h post injectio n, Twenty-two patients underwent laparotomy and samples of tumor and n ormal tissue were obtained, MAb 170H.82 correctly identified the prima ry tumor in 7 of 9 patients. Metastatic colorectal cancer was correctl y localized in 7 of 13 sites with biopsy confirmation. Interestingly, four patients with high, rising carcinoembryonic antigen levels exhibi ted positive MAb 170H.82 scans but metastatic colorectal cancer was no t confirmed at laparotomy. Three of these patients subsequently develo ped recurrent disease proximate to the area of increased radiolabel up take 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-MA b 170H.82 to detect metastatic colorectal cancer in some patients. Des pite these pharmacokinetic limitations, our study demonstrates that Tc -99m-MAb 17OH.82 may allow detection of occult colorectal cancer depos its prior to their recognition by conventional radiologic means in som e patients.