End-of-radiation PSA as a novel prognostic factor in patients undergoing definitive radiation for prostate cancer.

Abstract

68 Background: In patients with localized prostate cancer undergoing radiation therapy (RT) +/- androgen deprivation therapy (ADT), an end of radiation (EOR) PSA obtained during the last week of RT may serve as an early post-treatment predictor of poor outcomes and identify patients in whom to pursue treatment intensification or novel therapies. Methods: We reviewed an IRB-monitored, prospectively acquired database of patients with prostate cancer treated with definitive RT at our institution from 1993-2007 (n=890). Patients with an available EOR PSA were divided into two cohorts and analyzed separately based on inclusion of ADT into the treatment regimen. EOR PSA thresholds of 0.5 ng/mL and 1.0 ng/mL were explored. Multivariate analysis was performed to determine prognostic factors for biochemical failure-free survival (BFFS, Phoenix criteria) and overall survival (OS). Kaplan-Meier survival curves were constructed, with stratification by EOR PSA thresholds. Results: Median age was 69 years, with an even distribution of NCCN low risk (33.5%), intermediate risk (34.0%), and high risk (32.5%) patients. Median RT dose was 7020 cGy, and 54.5% were treated with ADT. Median follow-up of the entire cohort was 11.7 yrs. EOR PSA level was available for the majority of patients (77.5%). On multivariate analysis, EOR PSA >0.5 ng/mL was significantly associated with worse BFFS (p<0.0001) and OS (p<0.0001). In the subset of patients undergoing RT with ADT for NCCN intermediate/high risk disease, 5 yr BFFS was more disparate based an EOR PSA threshold of 0.5 ng/mL (5 yr BFFS: 87.3% vs. 41.1%, p<0.001), than initial NCCN risk level (5 yr BFFS: 88.7% vs. 76.9%, p=0.038). In NCCN low risk patients undergoing definitive RT alone, an EOR PSA threshold of 1.0 ng/mL was significantly prognostic of outcome (5 yr BFFS: 100.0% vs. 88.6%, p=0.024). Conclusions: For NCCN intermediate/high risk patients undergoing RT with ADT, EOR PSA >0.5 ng/mL may represent a better surrogate for poor outcomes than initial risk group. In addition, NCCN low risk patients undergoing RT alone who obtained an EOR PSA ≤1.0 ng/mL experienced excellent BFFS. Prospective evaluation of the utility of EOR PSA should be explored.