Long-Term Outcomes of Patients on a Phase II Prospective Trial of Oligometastatic Hormone-Sensitive Prostate Cancer Treated with Androgen Deprivation and External Beam Radiation

Abstract

<h3>Purpose/Objective(s)</h3> External beam radiation therapy (EBRT) to oligometastases may improve outcomes in patients (pts) with oligometastatic hormone-sensitive prostate cancer (oHSPC) who would traditionally receive androgen deprivation therapy (ADT) alone. To date, follow up (FU) on this cohort has been limited to ∼5 years. We reviewed the long-term outcomes of oHSPC pts treated with EBRT and ADT on an IRB approved prospective clinical trial (NCT00544830). <h3>Materials/Methods</h3> From 2006 to 2011, oHSPC pts with 1-5 metastases (mts) detected by CT and bone scan received 36 weeks of ADT (LHRH agonist + bicalutamide) and consolidative EBRT up to 53 Gy to all visible mts. When indicated, the primary tumor or prostate bed was treated with EBRT up to 78 Gy or 66 Gy, respectively. Primary objectives were long-term progression free survival (PFS), overall survival (OS) and local control of treated mts. <h3>Results</h3> 29 pts (median age 66.9, range 49.5-79.3) were treated on this protocol. Median number of mts per patient was 1 (range 1-5) and EBRT was administered to 51 lesions (37 bone, 10 pelvic lymph nodes [LNs], 4 non-pelvic LNs) to a median biologically equivalent dose of 53 Gy (range 47-66). Median Gleason score was 8 (range 5-10) and median baseline PSA was 11.4 (range 1.0-74.5). 15 pts had de novo mts, and 14 pts had oligorecurrent mts. 22 pts (75.9%) had bone mts. 25 pts (86%) reached PSA nadir of <0.2 within 9 months of completing ADT. Median FU was 9.9 years (yrs, range 0.2-14.4) for all pts. Median OS was 9.7 yrs (95% Confidence Interval [CI]:5.8-Not Reached [NR]) and 48.3% (95%CI: 29.5-64.8) at 10 years. Of the 10 pts (34%) still alive at last FU, two remain progression-free. Median PFS for all pts was 1.9 yrs (95%CI: 1.6-2.2) and 12.4% (95%CI: 3.4-27.6) at 10 years. Pts who presented with de novo mts had significantly improved (p=0.04) median PFS (2.0 yrs, 95%CI: 1.3-6.0) compared to oligorecurrent pts (1.8 yrs, 95%CI: 1.0-2.0). Pts who presented with LN only mts had improved (p=0.13) median PFS (5.8 yrs, 95%CI: 1.2-NR) compared to pts with bony mts (1.8 yrs, 95%CI: 1.3-2.0). For pts still alive after 5 years, median number of lines of treatment was 6 (range 0-15). At the time of FU, 16 pts (55%) had local control of all EBRT treated mts. Across all pts, 70.6% (n=36) of all treated mts were controlled. The mts that locally progressed had previously been controlled for median 3.4 yrs (range 1.7-10.5), comprising 11 bony mts, 2 pelvic LNs, and 2 non-pelvic LNs. <h3>Conclusion</h3> Our results compare favorably with other reported studies of oHSPC and provide new insights into their long-term outcomes. Metastasis-directed EBRT in this population of oHSPC pts resulted in longer than expected OS. The ongoing study adding radium-223 in addition to ADT and SBRT (NCT03361735) will seek to further delay recurrence in oHSPC with bone mts.