2-STEP IMMUNOSCINTIGRAPHY FOR NON-SMALL-CELL LUNG-CANCER STAGING USING A BISPECIFIC ANTI-CEA ANTI-INDIUM-DTPA ANTIBODY AND AN INDIUM-111-LABELED DTPA DIMER/

Immunoscintigraphy (IS) using anti-CEA F(ab')(2) monoclonal antibody ( MAb) is useful for improving mediastinal staging of nonsmall cell lung cancer (NSCLC), but the technique was limited because of an insuffici ent contrast between tumor and normal tissues. The aim of this study w as to determine if the method could be improved by a two-step method w hich uses a bispecific anti-CEA/anti-di-DTPA antibody (Bs-MAb) and In- 111-labeled di-DTPA-tyrosyl-lysine bivalent hapten. Methods: Twelve pa tients were intravenously given a 30 min Bs-MAb infusion (0.1 mg/kg). Four days later, they were injected intravenously with 0.1 mu g/kg hap ten labeled with 185 MBq In-111 (5 mCi). Images were recorded immediat ely and 6 and 24 hr after hapten injection. A pharmacokinetic analysis was performed. Surgery was performed 3 days after In-111-hapten injec tion, and samples of tumor and normal tissues were collected for immun ohistochemical and biodistribution studies. IS results were classified as true-positive CTP), false-positive (FP), true-negative (TN) or fal se-negative (FN) according to the surgical data Results: Primary tumor s were visualized in nine patients. The contrast was excellent, genera lly higher than that obtained with direct labeling of anti-CEA. In the mediastinum, IS results were (after surgery) five TN, two TP and one FP. One case remains undetermined. The FP result was due to a Bs-MAb u ptake in intrapulmonary lymph nodes. IS was in agreement with preopera tive staging in six of these nine patients and discordant in three. Co nclusion: Our study confirmed that the two-step method whith a bispeci fic antibody could greatly improve the performances of IS for lung can cer staging.