IMMUNOSCINTIGRAPHY WITH 3 STEP MONOCLONAL PRETARGETING TECHNIQUE IN DIAGNOSIS OF UVEAL MELANOMA - PRELIMINARY-RESULTS

Several problems still limit the full use of the diagnostic potential of immunoscintigraphy (IS) with technetium-99m labelled monoclonal ant ibodies (MoAbs) 225.28S directed to high molecular weight melanoma ass ociated antigen (HMW-MAA). The principal problem is the unfavourable r atio of tumour to nontumour activity (T/nT), due to the poor tumour up take and the high aspecific uptake of the tissue surrounding the tumou r. Recently, it was demonstrated that using the tumour pretargeting te chnique based on the injection of monoclonal antibody and the avidin/b iotin system (three step immunoscintigraphy), an improvement in the T/ nT ratio can be obtained in patients with carcinoembryonic antigen sec reting tumours. The aim of this study was to compare the diagnostic se nsitivity of traditional immunoscintigraphy with that of three step im munoscintigraphy in seven patients with uveal melanoma. All the patien ts underwent immunoscintigraphy with MoAb 225.28S radiolabelled with t echnetium-99m, and a three step immunoscintigraphy 1 week later. No pa tients demonstrated immediate toxic effects after receiving the reagen ts, no matter which of the two methods was used. The traditional immun oscintigraphy had a diagnostic sensitivity of 71.4%, diagnosing five o ut of seven melanomas tested. The three step study detected all the me lanomas examined (7/7) with a diagnostic sensitivity of 100% and showe d a drastic reduction in background. The preliminary results confirm t he feasibility of visualising the uveal melanoma and show that the thr ee step immunoscintigraphy is more diagnostically sensitive than tradi tional immunoscintigraphy, particularly in small lesions.