Background: ADT with salvage RT improves survival for men with PSA recurrence after RP. Current standard duration of ADT for high risk PSA recurrence is up to 2 years with RT; therefore shortening but intensifying systemic therapy may improve outcomes. The STREAM trial showed 6 mo of enzalutamide added to ADT/RT had a 3-year progression free survival (PFS) of 53% in high risk patients including lymph node (LN) positive. Given that docetaxel improves survival in men with mHSPC, we evaluated the combination of salvage RT, ADT/apalutamide and docetaxel in this setting. Methods: STARTAR is a multicenter phase 2 trial for salvage treatment of PSA recurrent PC following RP conducted within the US Dept. of Defense Prostate Cancer Clinical Trials Consortium (DOD PCCTC). Key inclusion criteria included PC with Gleason 7 with T3/positive margin/1-4 positive LNs or Gleason 8-10 disease and PSA relapse within 4 years of RP (min PSA 0.2 ng/mL to max PSA 4 ng/mL). Men with up to 4 positive resected LNs were eligible. Men started ADT with apalutamide, continued with RT (66-74 Gy to the prostate bed +/- pelvic LNs over 6-8 weeks), and finally completed docetaxel 75mg/m2 IV q3 weeks for 6 cycles. Men were treated with ADT and apalutamide for approximately 9 months. The primary endpoint was PSA PFS at 36 months. This interim analysis evaluated secondary endpoints of 1-year PSA recurrence, testosterone recovery, and safety of this treatment sequence. Results: From 3/2018 to 12/2019, 39 men were enrolled at Duke, Wake Forest, Cornell, and the GU Research Network. With a data cutoff in 9/2020, median follow up from enrollment was 14 months. Baseline patient characteristics included Gleason 4+3 = 7 in 54% and Gleason 8-10 in 46%, and 23% LN positive; median PSA at the time of enrollment was 0.58 ng/mL (range 0.21-3.40) and the median time from RP to enrollment was 7 mo (range 2-98). At 1 year, there have been no progression events with 38% (12/31) of men with post-treatment testosterone recovery into normal range (recovery time median 10 mos [1-17 mos]). Common adverse events (AEs) of any-grade at least possibly related to the regimen were 98% hot flashes, 88% fatigue, 77% alopecia, 57% dysgeusia, and 53% rash (28% grade 1; 15% grade 2, 10% grade 3), with neutropenia as the most common grade 3/4 AE (27/39 men, 70%) with two grade 3 febrile neutropenia. Conclusions: In this first phase 2 trial of ADT, apalutamide, radiation, and 6 cycles docetaxel in the salvage setting for high risk PSA recurrence, short term outcomes are excellent with no recurrences at 12 months of follow-up. This salvage treatment was well tolerated in the majority of men with the exception of a high rate of drug rashes and neutropenia related to the course of treatment, in line with known safety profiles of the study agents. Clinical trial information: NCT03311555