Clinical relevance of immunoscintigraphy with Tc-99m-labelled anti-CEA antigen-binding fragments in the follow-up of patients with colorectal carcinoma. Assessment of resectability by a combination of conventional imaging methods

Background and objective: Conventional imaging modalities (e.g. ultrasound, computed tomography [CT] and magnetic resonance [MRI]) are used in the routine follow-up of patients with colorectal carcinoma. But they have only limited diagnostic reliability. This study was undertaken to evaluate immunoscintigraphy (IS) with Tc-99m-labelled anti-CEA antigen-binding fragments (CEA-Scan(R)) alone or combined with conventional imaging methods. Patients and methods: 22 patients, operated on for colorectal carcinoma and suspected of having a recurrence, underwent scintigraphy with CEA-scan(R) and whole-body single-photon emission computed tomography (SPECT). All results were compared with those by computed tomography (CT) and, in 19 of the patients, with histological findings (surgical specimen or biopsy). The potential influence of the scintigraphic results on surgical management was analysed retrospectively with respect to the preoperative estimate of tumour resectability. Results: Lesion-based sensitivity of IS was 94%, diagnostic accuracy 92%, both being unrelated to the CEA serum level. When CT and IS were concordant regarding resectability, this estimate was correct in all instances. But in case of discordance the results of IS were verified operatively in 88% of cases. In no patient was there measurable immune reaction with formation of human-mouse-antibodies (HAMA). Conclusions: These results indicate that IS together with SPECT can achieve reliable and sensitive localisation of tumour lesions. CEA-Scan(R) does not, contrary to other murine antibodies, cause the formation of HAMA. The combination of IS with conventional imaging techniques can improve noninvasively the estimate of surgical resectability.