Anti-melanoma antibodies bind preferentially to diploid metastases in immunoscintigraphy

Immunoscintigraphy with 99Tcm-labelled anti-melanoma monoclonal antibody F(ab')2- fragments was performed in 23 patients with histologically verified metastatic melanoma. Immunoscintigraphy was positive in 14 patients and all known metastases were detected in eight patients, five of whom had only one lesion. Lesion localization and detectability were as follows: 12/13 (92%) cutaneous and subcutaneous, 11/14 (79%) lymph node, 5/7 (71%) bone, 3/6 (50%) lung and 1/5 (20%) abdominal metastases were visualized. Despite its high specificity--no false positive immunoscintigrams--the low sensitivity of this method in detecting deep metastases hampers its usability. The false negative results were not due to lack of antigen expression as positive immunostaining results were observed also in specimens from patients with negative immunoscintigrams. Flow cytometric analysis of the metastases revealed that in 7/8 (88%) patients with diploid tumours had positive immunoscintigrams but only 7/15 (47%) patients with aneuploid tumours. These results show that the diagnostic accuracy of melanoma immunoscintigraphy can be improved by selecting patients not only by testing for the antigen but also on the basis of DNA analysis of an accessible lesion.