The probability of a positive bone scan in patients who were treated with adrogen ablasio therapy for rising PSA after radical prostatectomy

4574 Background: Physicians often order periodic bone scans to check for metastases in patients treated with androgen ablation therapy (ADT) for rising PSA (biochemical recurrence; BCR) following radical prostatectomy. However, most of these scans are negative. We studied patient characteristics to build a predictive model for a positive scan (+BS) in that setting. Methods: From our prostate cancer database we identified all patients with detectable PSA after radical prostatectomy that were treated by ADT for BCR only. There were 511 BS performed in patients treated with ADT for BCR. Among them, 151 BS were performed for patients with BCR only with out previous evidence of bone metastases (1–8 BS for patient with median of one). We analyzed the following potential predictors for a positive bone scan at the time of each bone scan: preoperative PSA, history of neoadjuvant ADT (NA-ADT), time to BCR, pathologic findings (surgical margin, extracapsular extension, seminal vesicle invasion, lymph node metastases, and Gleason score), PSA before the BS (trigger PSA), PSA doubling time and time from BCR to BS. The results were incorporated into a predictive model. Results: Among the 151 BS, only 35 (23%) were positive for metastases. In multivariate analysis, only trigger PSA (P < 0.001, OR 1.84) and NA-ADT (P = 0.02, OR 1.32) predicted a +BS. Probability of +BS according to PSA of 0–2, 2.1–4, 4.1–10, 10.1–20 and above 20.1 were 4.7%, 15.3%, 29.6%, 46.1% and 63.3% respectively. A nomogram was constructed for predicting the probability of +BS, and was found to have a concordance index of 0.83. Calibration of the nomogram according to bootstrap analysis showed that the nomogram is reasonably accurate. Conclusions: Trigger PSA and a history of neoadjuvant ADT were associated with a +BS. Omitting scans in low-risk patients could reduce substantially the number of scans ordered. No significant financial relationships to disclose.