Immunoscintigraphy of Adenocarcinomas by Means of Radiolabeled F(ab′)2 Fragments of an Anti-Carcinoembryonic Antigen Monoclonal Antibody: A Multicenter Study

F(ab′)2 fragments of anti-carcinoembryonic antigen (CEA) monoclonal antibody P023C5, determined to be more suitable than intact IgG and Fab fragments for immunoscintigraphy, were labeled with 131I or conjugated to DTPA for instant “In-labeling, and administered i.v. (2-3 mCi/ 0.5 mg) to 509 patients in 11 nuclear medicine departments: 284 patients had gastrointestinal adenocarcinomas, 204 had nongastrointestinal adenocarcinomas and 21 were controls; serum CEA was elevated in 169 patients, normal in 115, and not determined in 225. The following results were obtained: (a) no adverse reactions; (b) tumor imaging in 324 patients (in particular, in 81.5% CEA-seropositive and in 69.0% CEA-seronega-tive patients); (c) no significant difference in sensitivity among the results of the 11 departments; (d) no significant difference in overall sensitivity between 131I- and “In-labeled immunoradiopharmaceuticals; (e) the fraction of documented lesions imaged was 733% in CEA-seropositive and 53.7% in CEA-seronegative patients; (/) the detection of liver metastases was hampered, particularly when using the ! “In-labeled reagent, by nonspecific radioactivity uptake; (g) the major cause of negative immunoscintigraphy results was a lack of CEA in tumor lesions, as documented by immunohistochemistry; (h) lesion size is also important since the sensitivity was 64% for lesions up to 2 cm in diameter and 84% for larger lesions; (i) many “unexpected” radiolocalizations were recorded. Most were identified as occult tumor lesions. In 35 patients, this finding contributed to the early detection of tumor recurrences.