RADIOLABELED MONOCLONAL-ANTIBODY INDIUM 111-LABELED CYT-356 LOCALIZESEXTRAPROSTATIC RECURRENT CARCINOMA AFTER PROSTATECTOMY

Objectives. The sites of recurrent carcinoma of the prostate were loca lized with radiolabeled monoclonal antibody, and these sites were corr elated with the response of patients treated with pelvic radiation aft er prostatectomy. Methods, Radionuclide scans were performed with indi um 111-labeled CYT-356, a monoclonal antibody that binds to prostate e pithelial cells, in 48 men diagnosed with recurrent carcinoma detected by prostate-specific antigen (PSA) screening after radical retropubic prostatectomy. Results. In 48 patients with recurrent carcinoma detec ted by PSA screening following radical retropubic prostatectomy, 73% h ad monoclonal antibody activity beyond the prostatic fossa, and only 3 patients (6%) had activity in the prostatic fossa alone; 65% had mono clonal antibody activity in pelvic lymph nodes despite the fact that l ymph node dissections were pathologically negative at the time of pros tatectomy in 90% of the patients; and 23% of patients had monoclonal a ntibody activity in abdominal and extrapelvic retroperitoneal nodes. O f 48 patients, 13 underwent external beam radiation therapy after mono clonal antibody scans. Six patients had scans showing activity beyond the field of radiation, and radiation therapy failed in 4 of these pat ients. Seven patients had scans with no activity beyond the field of r adiation therapy, and radiation therapy failed in only 2 of these pati ents. Conclusions. The scans frequently show monoclonal antibody uptak e in pelvic, abdominal, and extrapelvic retroperitoneal sites beyond t he region of limited obturator node dissections and may account for th e understaging and subsequent failure of radical prostatectomy in some patients. The monoclonal antibody scan seems to be a good predictor o f which patients will respond to radiation therapy after radical prost atectomy, but because these patients often have nodal activity beyond the radiated field, this initial response may not be curative. (C) 199 8, Elsevier Science Inc. All rights reserved.