Pelvic clinical node-positive prostate cancer: Impact of radiotherapy and nodal disease burden.

Abstract

338 Background: The optimal management of pelvic clinical node-positive (cN1) prostate cancer remains controversial and randomized evidence for local therapy is lacking. Recent data suggests that common iliac nodal metastases (CIM), while technically constituting M1a disease, are more common than previously recognized and might carry a prognosis similar to that of cN1 disease when treated radically. In this context, we reviewed the experience at our center of treating cN1 prostate cancer, with or without CIM, focusing on the role of radiotherapy (RT) and measures of nodal disease burden. Methods: The study population consisted of men diagnosed between 2002 and 2018 with prostate cancer with cN1 disease and/or CIM and treated with androgen deprivation therapy and/or definitive local therapy. Outcomes of interest included overall survival (OS) and castration resistance-free survival (CRFS), which were estimated using the Kaplan-Meier method. Univariate and multivariate Cox regression were used to identify factors associated with OS and CRFS. In the subgroup of patients treated with RT, the association between a number of RT characteristics – including biologically effective dose (BED) to the prostate, use of elective pelvic nodal RT, and escalated dose (RT boost) to positive nodes – and OS was studied. Results: A total of 87 patients were included, of whom 14 had CIM and 68 received RT. Median follow-up was 110 months. On univariate analysis, RT was associated with improved OS (hazard ratio [HR] 0.28, 95% CI 0.14-0.55, p<0.0005) and CRFS (HR 0.22, 95% CI 0.12-0.41, p<0.0005). Median OS in patients receiving RT was 134.9 months versus 63.1 months in those not receiving RT. Receipt of RT remained significantly associated with OS on multivariate analysis (HR 0.12, 95% CI 0.05-0.31, p<0.001). Biopsy Gleason score 10 and presence of >2 positive lymph nodes were associated with worse OS while presence of CIM was not associated with OS. In patients treated with RT, increasing BED to the prostate was associated with improved OS (HR 0.73 per 10 Gy increase, 95% CI 0.54-0.97, p=0.03) while use of elective pelvic nodal RT and use of an RT boost to positive nodes were not associated with OS. Conclusions: This is the first cohort to evaluate the impact of RT in pelvic clinical node-positive prostate cancer that includes CIM. Receipt of RT was associated with improved oncologic outcomes. The number of positive pelvic nodes, but not their common iliac location, was prognostic and warrants further investigation in a larger dataset.