A thousand points of light or just dim bulbs? Radiolabeled antibodies and colorectal cancer imaging

Radioimmunoscintigraphy (RIS) is coming into its own as an imaging modality in clinical oncology. Ear ly experience with indium-111-labeled intact int act murine monoclonal antibodies (MoAbs) in colorectal cancer, suggested th at RIS images hepatic metastases poorly. Moreover, an antimurine immune res ponse was frequently provoked, precluding multiple follow-up RIS studies in individual patients due to reticuloendothelial sequestration of the radioi mmunoconjugate before tumor targeting could occur: Recent trials of technet ium-99m-labeled antibody fragments and human MoAbs have demonstrated signif icant improvement in imaging efficacy, ann repeated or serial imaging is po ssible because of the absence of associated immunogenicity. RIS is demonstr ably more sensitive than conventional diagnostic modalities (CDM) such as c omputed tomography (CT)for detection of extrahepatic abdominal and pelvic c olorectal carcinoma and is complementary to CDM in imaging liver metastases . In a surgical decision-making analysis comparing CT, RIS (IMMU-4 Tc-99m-F ab'; CEA-Scan(R)), and CT plus RIS in patients with recurrent or metastatic colorectal cancer CT plus RIS improved correct prediction of, resectabilit y by 40% and correct prediction of unresectability by 100% compared with CT alone. At the present time, RIS used in combination with CDM contributes a n incremental im improvement in diagnostic accuracy in colorectal cancer pa tients with known or suspected recurrent disease. Basic and clinical resear ch currently in progress promises to yield agents and methods that provide rapid high-resolution imaging, high tumor-to-background ratios in all organ s at risk for tumor recurrence or metastasis, negligible immunogenicity and toxicity, and a significant further improvement in the accuracy of clinica l decision making in oncology patients.