Evaluation of preoperative ProstaScint™ scans in the prediction of nodal disease

Abstract

Diagnostic methods are limited for detecting microscopic soft tissue metastases in patients with prostate cancer. Previous studies using ¹¹¹Indium Capromab Pendetide (ProstaScint™ scan) analyzed patients with extensive localized tumor (prostate specific antigen (PSA) >20 ng/ml) not optimal for surgical therapy. We evaluated the role of the ProstaScint™ scan in a preoperative population to provide histological documentation and to assess its utility in a surgical population. A total of 22 preoperative patients, underwent a ProstaScint™ scan. The mean preoperative PSA was 16.0 ng/ml (range 3.9–33 ng/ml). The mean Gleason score at biopsy was 6.9 (range 6–9). Each patient underwent a radical retropubic prostatectomy and bilateral pelvic lymph node dissection, which included resection of both obturator and common iliac lymph nodes. Histologic analysis of the resected lymph nodes provided the standard of comparison with the ProstaScint™ scan. The results of the scan and pathology for all 22 patients were compared with the bilateral obturator and iliac nodes, creating 88 data points. Nine areas (10%) were positive on the scan. One of these (11%) was a true positive while the other eight (89%) were false positives. Seventy-nine areas (90%) were negative on scan results. Of these, five areas (6%) were false negatives and 74 areas (94%) were true negatives. The scan yielded a sensitivity of 17%, specificity of 90%, negative predictive value (NPV) of 94% and a positive predictive value (PPV) of 11%. The high false positive rate and low PPV of ProstaScint scans overestimates metastatic lymph nodes disease, and is not useful when used preoperatively.