Impact of clinical staging based on DRE versus imaging (TRUS/MRI) in localized prostate cancer risk assessment.

Abstract

227 Background: The Cancer of the Prostate Risk Assessment (CAPRA) score is a validated risk assessment tool for biochemical recurrence (BCR) risk after radical prostatectomy (RP) for localized prostate cancer. The score is calculated using five clinical variables: age, PSA at diagnosis, Gleason score pattern, percentage of positive biopsy cores, and clinical stage by digital rectal exam (DRE). Since its publication in 2005, transrectal ultrasonography (TRUS) and magnetic resonance imaging (MRI) have increasingly been used in clinical evaluation but have yet to be integrated into prostate cancer tumor staging rules or risk-stratification models. We incorporated both clinical- and imaging-derived stage into the CAPRA score to assess the association between the base and imaging-adjusted CAPRA model and the outcome of BCR. Methods: We performed a retrospective analysis of patients who underwent RP for prostate cancer staged ≤T3a on both DRE and imaging (TRUS/MRI) and diagnosed between 2000-2017 at our institution. DRE was treated as a binary variable (T1 vs ≥T2) as was imaging (≤T2 vs T3a). BCR was defined as 2 consecutive PSA ≥0.2 ng/ml starting 8 weeks post-surgery or receipt of salvage treatment. Two CAPRA scores were computed: one with DRE-derived and one with image-based T-stage. Life table estimates were used to evaluate likelihood of BCR-free survival after RP stratified by CAPRA scores. We performed Cox regression to examine the association between clinical CAPRA components and BCR risk and to determine whether stratifying clinical T1, T2, and T3a disease in CAPRA was independently associated with BCR risk on multivariate analysis. Results: Of 1972 patients studied, 103 (5%) had upstaging in CAPRA risk group with imaging-reported clinical stage. Life table estimates were comparable between DRE- and imaging-based CAPRA score with regard to likelihood of BCR-free survival. In separate unadjusted Cox regression models, DRE-based (HR 1.57; 95% CI 1.50-1.64) and imaging-based clinical CAPRA (HR 1.56; 95% CI 1.50-1.63) were both independently associated with risk of recurrence after RP and model fit did not differ significantly. On multivariable Cox regression adjusted for CAPRA component variables, clinical stage ≥T2 on DRE (HR 1.28; 95% CI 1.06-1.54) and T3a on imaging (HR 1.79; 95% CI 1.47-2.19) were independently associated with BCR risk. Conclusions: Both DRE- and imaging-based clinical CAPRA nomograms are associated with risk of BCR after RP for prostate cancer. On multivariable analysis, both modalities of clinical staging are independently associated with CAPRA score on the risk assessment nomogram. Each staging modality offers independent prognostic information, which supports the continued use of DRE-based clinical staging in prostate cancer risk stratification and demonstrates the potential benefit imaging-based clinical stage may add to these models and to tumor staging standards.