Pretargetted imaging of colorectal cancer recurrences using an 111In-labelled bivalent hapten and a bispecific antibody conjugate.

In 11 patients recurrence of colorectal cancer was suspected by a rise in serum carcinoembryonic antigen (CEA) (nine cases), by a subocclusive clinical situation (one case) or by endoscopy (on an anastomosis, one case). Two-step tumour targetting was performed by a first injection of 0.1 mg kg-1 of unlabelled bispecific antibody conjugate (an anti-CEA Fab' fragment chemically coupled to an anti-diethylene triamine pentaacetate (DTPA)-indium fragment) followed 4 to 5 days later by injection of the bivalent DTPA hapten labelled with 5 to 8 mCi 111In.