Introduction

Despite documented oncological benefit, postoperative adjuvant radiotherapy (aRT) utilization in prostate cancer (PCa) patients is still limited in the US. We aimed to develop and internally validate a risk stratification tool incorporating the Decipher genomic score, along with routinely available clinicopathologic features, to identify patients who would benefit the most from aRT

Methods

512 PCa patients treated with RP at four US academic centers between 1990-2010. All patients had pT3a disease, positive margins, and/or pathologic lymph node invasion (LNI). Multivariable Cox regression analysis tested the relationship between available predictors (including Decipher score) and clinical recurrence (CR), which were then used to develop a novel risk stratification tool. Our study adhered to the TRIPOD guidelines for development of prognostic models

Results

Overall, 21.9% patients received aRT. Median follow-up in censored patients was 8.3 years. The 10-year CR rate was 4.9% vs. 17.4% in patients treated with aRT vs. initial observation (p<0.001). Pathological T3b/T4 stage, Gleason score 8-10, LNI and Decipher score >0.6 were independent predictors of CR (all p<0.01). A novel nomogram (Figure 1) based on these risk factors had a c-index of 0.85, with optimal calibration characteristics. Cumulative number of risk factors was 0, 1, 2, and 3-4 in 46.5, 28.9, 17.2, and 7.4% of patients respectively. aRT was associated with decreased CR rate in patients with ≥2 risk factors (10-year CR rate 10.1% in aRT vs. 42.1% in initial observation, p=0.008, number needed to treat=3.1), but not in those with <2 risk factors (p=0.23, Figure 2).

Conclusions

Utilizing the novel model to indicate aRT might reduce overtreatment, decrease unnecessary side effects, and reduce risk of CR in the subset of patients (~25% of all patients with aggressive pathological disease) who really benefit from this therapy. _x000D_

Funding

none