A biopsy-based genomic classifier to predict biochemical failure after definitive radiation without hormone therapy in a prospective cohort of intermediate risk prostate cancer.

Abstract

68 Background: Recently, NCCN adopted the Zumsteg-Spratt subclassification to define NCCN favorable and unfavorable intermediate-risk prostate cancer (IR-PCa). NCCN unfavorable disease is recommended to receive combination androgen deprivation therapy (ADT) and radiotherapy. To determine if genomics could help identify a subset who may safely avoid ADT, we evaluated the Decipher genomic classifier (GC) in IR-PCa treated with dose-escalated image-guided radiotherapy (DE-IGRT) alone. Methods: Our cohort comprised of 121 patients with NCCN favorable (N = 49, 40%) and unfavorable (N = 74, 60%) IR-PCa, who received 78 Gy without ADT. Diagnostic needle biopsies with the highest Gleason score (GS) and %tumor involvement were macrodissected for RNA extraction. GC scores were determined from the Decipher prostate cancer classifier assay (GenomeDx Biosciences, San Diego, CA). Primary clinical endpoint was biochemical relapse ([BCR], PSA nadir + 2ng/ml) post-DE-IGRT. We compared association with BCR against known clinicopathologic prognostic indices and the NCCN risk strata. Results: With a median follow up of 7.5y, 24 (19%) patients experienced BCR. Individual clinical indices did not predict BCR-free survival rate (BFS). NCCN risk strata was however associated with a small but significant difference in BFS (5-y 93%, favorable vs 88%, unfavourable, P = 0.046). GC scores stratified 85 (70%), 19 (16%), and 17 (14%) men into low, intermediate, and high risk of recurrence; 5-y BFS were 95%, 89%, and 59%, respectively (P < 0.001). On multivariable analysis, a hazard ratio of 4.71 (95% CI 1.81-12.28, P = 0.0015) for BCR was observed for the GC high risk group compared to low/intermediate; NCCN risk strata and intraductal variant did not achieve significance. Conclusions: In IR-PCa men treated with DE-IGRT monotherapy, Decipher GC was an independent predictor of BCR. While most men in this our cohort were stratified as NCCN unfavorable IR-PCa, the majority were GC low risk with excellent outcomes from DE-IGRT alone. In contrast, a minority with GC high risk had suboptimal outcomes, and may benefit from ADT intensification.