Identification of low prostate-specific antigen, high Gleason prostate cancer as a unique hormone-resistant entity with poor survival: A contemporary analysis of 640,000 patients.

5080 Background: The clinical implications of a low prostate-specific antigen (PSA) in high-grade prostate cancer are unclear. We examined the prognostic and predictive value of a low PSA in high-grade prostate cancer. Methods: We identified 642,975 patients in the National Cancer Database (n = 491,505) and Surveillance, Epidemiology, and End Results program (n = 151,470) with localized or locally advanced prostate cancer from 2004-2013. Patients were stratified by Gleason score (8-10 vs. ≤7) and PSA (≤2.5, 2.6-4.0, 4.1-10.0, 10.1-20.0, and > 20.0 ng/mL) for analyses. Multivariable Fine-Gray competing risks and Cox regressions were used to analyze prostate-cancer specific mortality (PCSM) and all-cause mortality (ACM), respectively. Results: 5.6% of Gleason 8-10 tumors were diagnosed with PSA ≤2.5 ng/mL. Among Gleason 8-10 disease using PSA 4.1-10.0 ng/mL as referent, PCSM was U-shaped with respect to PSA, with adjusted hazard ratio (AHR) of 1.75 (95% CI 1.05-2.92, P = 0.032) for PSA ≤2.5 ng/mL vs. 1.31, 0.88, and 1.60 for PSA 2.6-4.0, 10.1-20.0, and > 20.0 ng/mL. In contrast, PCSM was linear for Gleason ≤7 disease with AHR of 0.32 (95% CI 0.10-1.00, P = 0.050) for PSA ≤2.5 ng/mL vs. 1.13, 1.69, and 3.22 for PSA 2.6-4.0, 10.1-20.0, and > 20.0 ng/mL (PGleason*PSA interaction< 0.001). Gleason 8-10 disease with PSA ≤2.5 ng/mL had a much higher risk of PCSM than standard NCCN high-risk disease (AHR 1.92, 95% CI 1.18-3.14, P = 0.009; 47-month PCSM 14.0% vs. 10.5%). For Gleason 8-10 tumors treated with definitive radiotherapy, androgen deprivation therapy (ADT) was associated with decreased ACM for PSA > 2.5 ng/mL (AHR 0.87, 95% CI 0.81-0.94, P < 0.001) but trended toward increased ACM for PSA ≤2.5ng/mL (AHR 1.27, 95% CI 0.89-1.81, P = 0.194; PADT*PSA interaction= 0.026). Conclusions: Low PSA, high-grade prostate cancer appears to be a unique hormone-resistant entity with a high risk of PCSM that responds poorly to standard treatment. Further molecular classification and trials are urgently needed to develop biological insight into this entity and establish new treatment paradigms, potentially including chemotherapy or novel systemic agents.