IMMUNOSCINTIGRAPHY WITH A NEW INDIUM-111-LABELED MONOCLONAL-ANTIBODY (MAB 1A3) IN PATIENTS WITH COLORECTAL-CANCER

PURPOSE: This study was designed to evaluate a new anticolorectal carc inoma monoclonal antibody (1A3), conjugated with the bifunctional chel ating agent N,N'-bis(2-hydroxybenzyl) 1 oacetamidobenzyl)1,2-ethylened iamine-N,N'-diacetic acid and labeled with indium-111, in a Phase I/II study involving 38 patients with localized or advanced colorectal can cer. METHODS: Patients were injected with indium-111-N,N'-bis(2-hydrox ybenzyl) 1 (4-bromoacetamidobenzyl) 1,2-ethylenediamine-N,N'-diacetic acid-monoclonal antibody 1A3 (1-50 mg, 1-5 mCi) and imaged at two or t hree sessions one to five days later. Scintigraphic findings were comp ared with radiologic, pathologic, surgical, and other clinical finding s to assess the accuracy of radioimmunoscintigraphy. RESULTS: At least one known tumor site was clearly defined by planar scintigraphy in 29 (76 percent) patients. Increased radioactivity was seen in 40 of 63 k nown tumor sites (37/43 abdominal-pelvic, 3/15 hepatic, and 0/5 pulmon ary sites) without any apparent dose-related effects. Nineteen previou sly undetected sites were considered positive by imaging, and, of thes e, six were biopsy-proven tumor sites, four were probable tumor sites, three a ere definitely false positive sites, and six were probable fa lse positive sites. Radioimmunoscintigraphy detected proven tumor in 1 5 of 16 patients with negative or equivocal computed tomography result s. Of the 28 patients with rectosigmoid cancer, 25 (89 percent) had po sitive studies with 34 of 47 tumor sites showing definite uptake on th e scintigrams. This included 3 of 9 hepatic metastases. The only adver se reaction occurred in one patient who developed transient hives. Hum an anti-mouse antibody responses occurred in approximately one-half of the patients injected with doses of 10 or 50 mg. CONCLUSION: This stu dy shows that radioimmunoscintigraphy with this indium-111-labeled mon oclonal antibody is safe, it can detect most nonhepatic abdominal-pelv ic tumors with a positive predictive value of 83 (44/53) percent, and it should prove to be useful, particularly in the diagnosis of recurre nt rectal carcinoma.