ASCO GU 2018: Can free PSA be used as a biomarker in biochemical recurrence after surgery to predict CRPC?

San Francisco, CA ( Dr. Goldberg and colleagues from the Princess Margaret Cancer Centre in Toronto, Canada presented results of assessing free PSA in the setting of biochemical recurrence (BCR) after radical prostatectomy for predicting time to CRPC. PSA produced from prostate cancer cells escapes proteolytic processing, resulting in a more complexed PSA and a lower %free PSA (%fPSA). Higher %fPSA correlates with lower prostate cancer risk. However, the role of fPSA in BCR after radical prostatectomy is unknown, thus forming the objective of this study.

For this study, the authors utilized an institutional database of prostate cancer patients in the last decade that had BCR after radical prostatectomy and had at least one fPSA measurement. Patients were stratified according to the fPSA ratio cut-off of 0.15. Data collected included demographics and clinicopathologic parameters including radical prostatectomy pathology and adjuvant/salvage treatments. Clinical endpoints included time to ADT, CRPC and metastasis as well as cancer specific survival. Multivariable logistic regression analysis was performed to predict covariates associated development of CRPC.

A total of 305 men with BCR fitting inclusion criteria were identified, including 188 (61.6%) with a fPSA ratio <0.15 (Group 1) and 117 (38.4%) with a fPSA ratio ≥ 0.15 (Group 2). Interestingly, 31% (Group 1) vs. 58% (Group 2) developed CRPC (p<0.001), and the time to reach CRPC from surgery was much shorter in Group 2 (79 months) vs. Group 1 (96 months), p=0.033. Additionally, 67% of Group 2 patients vs. 43% of Group 1 patients developed metastasis (p<0.001). Finally, median cancer specific survival was 188 months for Group 2 patients and not reached for Group 1 patients (log rank test p<0.0001). Multivariable logistic regression analysis demonstrated that secondary Gleason score of 5 (vs 3) and %fPSA ≥ 0.15 predicted CRPC status (OR 11.63, 95%CI 1.38-97.4; OR 7.99, 95%CI 2-31.95, respectively).

Dr. Goldberg concluded that %fPSA ≥ 0.15 in the setting of BCR confers a more aggressive disease, manifesting in a faster development of CRPC, metastasis and death. These findings suggest a reversal in the significance of %fPSA values in BCR patients compared to pre-diagnosis, and should be validated in larger cohorts.

Speaker: Hanan Goldberg, University of Toronto, Princess Margaret Cancer Centre, Toronto, Canada

Co-Authors: Ally Hoffman, Teck Sing Woon, Zachary William Abraham Klaassen, Thenappan Chandrasekar, Douglas Cheung, Alejandro Berlin, Rashid Sayyid, Neil Eric Fleshner

Written by: Zachary Klaassen, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, Twitter:@zklaassen_md at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA