SABR in high-risk prostate cancer: Outcomes from two prospective clinical trials with and without elective nodal irradiation.

Abstract

3 Background: There is limited data on SABR in high-risk prostate cancer (PCa) especially regarding the role of elective nodal irradiation (ENI). This study compares two prospective phase II trials using SABR in high-risk prostate cancer, with and without ENI. Methods: Both trials enrolled patients with high-risk PCa only. Trial1 (pHART8) patients received 40Gy/5 to the prostate and 30Gy/5 to the seminal vesicles. Trial2 (SATURN) patients received 40Gy/5 to the prostate and 25Gy/5 to the pelvis and seminal vesicles. CTCAE and RTOG toxicities were collected. Biochemical failure (BF) was defined as nadir+2 and 4-year PSA response rate (4yPSARR) was < 0.4 ng/ml. Results: 60 patients were included (pHART8, n=30; SATURN, n=30). Median follow-up was 5.6y and 4.0y. Median nPSA was 0.02ng/ml for both. Six patients had BF, all from pHART8; four were managed with ADT and two are being observed. The BF rate was 14.6% at 5y in pHART8 and 0% in SATURN. All six biochemical failures were associated with a PSA of ≥ 0.4 ng/ml at 4y. 63% of patients in pHART8 and 93% in SATURN had a 4yPSARR. BF probability at 5y was 0% for those achieving a 4yPSARR, and 35.1% if not (p = p < 0.0001). Two patients died in pHART8, one from metastatic disease. One patient in SATURN died from other causes. No other patients developed metastatic disease, and one patient in pHART8 had CRPC. OS at 5y was 93.2% and 96.7% (p=0.86). There was significantly worse late GI and sexual toxicity in pHART8, but no difference in late GU toxicity between the two trials. Conclusions: SABR in high-risk prostate cancer yields biochemical control rates that are comparable to other radiotherapy modalities. ENI using SABR is feasible and led to a significant improvement in biochemical control as well as in 4yPSARR which proved to be a predictor of biochemical control, without an increase in late GI or GU toxicity. Longer follow-up would provide a better assessment of biochemical control. Clinical trial information: NCT01505075 and NCT01953055.