PILOT-STUDY EVALUATING THE INTRAOPERATIVE LOCALIZATION OF RADIOLABELED MONOCLONAL-ANTIBODY CC83 IN PATIENTS WITH METASTATIC COLORECTAL-CARCINOMA

Background. CC83, a second-generation monoclonal antibody (MAb) agains t tumor-associated glycoprotein TAG-72 has been shown to have a higher affinity constant than the anti-TAG MAbs CC49 and B72.3. Clinical stu dies have shown the effectiveness of both CC49 and B72.3 radiolabeled MAbs in localizing colorectal carcinoma with a hand-held gamma-detecti ng probe during operation. This current study was designed to assess t he safety and tumor-binding ability of radiolabeled CC83 MAB in this s etting. Methods. Seventeen patients with recurrent colorectal cancer u nderwent intravenous injection with CC83 MAb radiolabeled with iodine 125 (2.0 mCi I-125/0.2 mg CC83 MAb). Exploratory laparotomy was carrie d out 21 to 28 days after injection, consisting of a thorough traditio nal exploration followed by a survey with a hand-held gamma-detecting probe. All traditionally suspicious and probe-positive tissue was eith er Biopsied or resected and subsequently examined for the presence of carcinoma by using routine histochemical staining techniques. Results. Thirty-two sites were identified as suspicious for cancer by traditio nal surgical exploration and 39 through intraoperative survey with a h and-held gamma-detecting probe in the seventeen patients completing th e study. Biopsy or resection yielded 27 tumor sites when tissue was ev aluated by using routine hematoxylin-eosin staining. All 27 tumor site s were localized by the radiolabeled CC83 MAb, whereas 12 additional s ites were RIGS positive but hematoxylin-eosin negative, resulting in a sensitivity and positive predictive value of 100% and 69%, respective ly. Traditional methods of exploration detected 23 of 27 tumor sites ( 85% sensitivity), and nine false-positive sites were recorded (72% pos itive predictive value). Occult tumor was found by using CC83 MAb in f our (15%) of 27 sites, altering the surgical plan in three patients. C onclusions. This initial study indicates that CC83 MAb, when used with RIGS, is safe and sensitive in detecting recurrent intraabdominal col orectal cancer.