RADIOIMMUNOSCINTIGRAPHY WITH (111)INDIUM LABELED CYT-356 FOR THE DETECTION OF OCCULT PROSTATE-CANCER RECURRENCE

We assessed the safety and ability of the (111)indium labeled immunoco njugate -glycyl-tyrosyl-(N,e-diethylenetriaminepentaacetic acid)-lysin e (CYT-356) to detect sites of occult prostate cancer in 27 subjects w ho had undergone radical prostatectomy and whose only evidence of recu rrent disease was an increasing (0.8 ng./ml. or greater) serum prostat e specific antigen (PSA). All subjects underwent whole body scintigrap hy between 2 and 4 days following the radiopharmaceutical injection. R outine blood work and human anti-mouse antibody titers were monitored. Scintigraphic findings were compared with clinical parameters, prosta tic fossa biopsy results and conventional imaging techniques. Except f or transient hypotension in 1 subject following the second infusion, n o side effects or human anti-mouse antibody titers were detected. In 2 2 subjects 1 or more lesions were detected, of which 11 (50%) were con firmed by biopsy, computerized tomography or magnetic resonance imagin g. Of 14 subjects with lesions in the prostatic fossa 13 had biopsies performed, 8 (62%) of which were positive. Magnetic resonance imaging confirmed tumor in the spine and chest computerized tomography finding s were compatible with lesions seen in the mediastinum in 1 subject ea ch. There was a statistically significant relationship between detecti ng a scan abnormality and the initial pathological stage of disease bu t not with the serum PSA. These data provide preliminary evidence that (111)indium labeled CYT-356 can be safely administered and readminist ered, and it detects sites of occult prostate cancer recurrence in sub jects whose PSA is increasing following radical prostatectomy.