IN-111 LABELED B72.3 MONOCLONAL-ANTIBODY FOR RADIOIMMUNOSCINTIGRAPHY IN COLORECTAL-CANCER

Radioimmunoscintigraphy (RIS) was conducted using the In-111-labeled B 72.3 monoclonal antibody in the follow-up of colorectal cancer patient s. B72.3 is directed against the tumor-associated glycoprotein (TAG 72 ) which is expressed by most adenocarcinomas. In Europe, B72.3 has bee n available as OncoScint CR-103(R) (EuroCetus, Amsterdam, The Netherla nds) since 1991. Imaging procedures in this study included scintigraph ic investigation (whole body and single images) at 30 min, 24, 48, 72, 96 and 120 h post injection emission computed tomography at 24 and 48 h, as well as a T-CT (DR 2, Siemens) of the lower abdomen. 12 patient s with a history of surgery for colorectal cancer and suspected tumor recurrence were studied thus far. All patients were in clinical follow -up after surgical treatment of the primary tumor. In 9 of the 12 pati ents a final diagnosis was possible (additional surgery and biopsy wit hin 4 weeks after RIS, follow-up with repeated T-CT, endoscopy, sonogr aphy, and clinical status). In 3 patients the final diagnosis still re mained unclear due to a too short follow-up period of less than 3 mont hs. RIS was able to detect 3 of 4 proven recurrences (T-CT: 2); in 5 p atients RIS was true negative (T-CT: 5). In 1 case it was false negati ve (T-CT: none) and in 3 cases (T-CT: 3) where RIS was negative a fina l diagnosis has not yet been established. RIS, however, was unable to detect liver metastases as focally increased activities, whereas the T -CT showed 3 true positive cases. RIS revealed 4 true negative (T-CT; 5), 3 false negative (T-CT; none) and 5 equivocal (T-CT: 4) findings i n patients with suspected liver metastases. The preliminary results ar e encouraging. So far, no false-positive results occurred and the dete ction rate of local recurrence is comparable with that of T-CT. A diff erentiation between tumor mass and scar or granulation appears to be p ossible. An advantage of RIS is the noninvasive nature of the scintigr aphic technique so that it can be conducted before an eventual T-CT-gu ided biopsy is per formed.