Background: Consolidation durvalumab after chemoradiation (CRT) is the new standard of care in locally advanced NSCLC (LA-NSCLC). We hypothesized that adding immunotherapy concurrently with CRT (cCRT) would increase efficacy without significant additive toxicity. To test this concept, we conducted a phase II trial called DETERRED combining atezolizumab (atezo) with cCRT followed by consolidation full dose carboplatin/paclitaxel (CP) with atezo (CP-atezo) for 2 cycles and then maintenance atezo for 1 year. The primary endpoint was safety/toxicity and feasibility. Methods: This study enrolled patients (pts) between February 2016 - April 2018 and was done in two parts: In part 1 (N=10), conventionally fractionated CRT (60-66 Gy in 30-33 fractions combined with weekly low dose CP) was followed by CP-atezo then maintenance atezo. Part 2 was cCRT (N=30) with atezo followed by CP-atezo then maintenance atezo. Atezo was given at 1200 mg IV Q3 weeks. Severe adverse events (SAEs) ≥ grade 3 were defined by CTCAE v5.0. Evaluable pts received at least one dose of atezo. PD-L1 staining utilizes the DAKO 22C3 platform. Kaplan Meier were analyzed for progression free survival (PFS) and overall survival (OS), and chi-square test for PD-L1 levels on any recurrence, with significance set at <0.05. Results: In Part 1, atezo related SAEs were seen in 4 pts (40%) (2 grade 3 arthralgia, 1 grade 3 dyspnea and 1 grade 5 TE fistula). Grade 2 radiation pneumonitis (RP) was seen in 1 pt. In Part 2, seven (23%) pts had atezo related SAEs (diarrhea, nephritis, dyspnea, fatigue and heart failure). RP was seen in 3 pts, 2 grade 2 and 1 grade 3, which led to atezo discontinuation. In Part 1, with an overall median follow up (f/u) time of 22.5 months and 27.4 months for survivors, the 1-year PFS is 50%, and OS is 79%. In part 2, with a median f/u time of 11.8 months and 13.7 months for survivors, the 1-year PFS was 57%, and OS is 79%. Baseline tumor biopsy PD-L1 status was evaluable for 34 pts. There were no significant differences in cancer recurrence for PD-L1 <1% (7/16=44%) vs ≥1% (6/18=33%), or for the PD-L1 cutoff of <50% (11/26=42%) vs ≥50% (2/8=25%). Conclusions: Concurrent atezo with CRT followed by CP-atezo and maintenance atezo is safe without increased toxicities compared to CRT alone followed by CP-atezo and maintenance atezo. Updated efficacy results from DETERRED will be presented. Ultimately, the clinical benefit of immunotherapy with cCRT followed by consolidation chemo-immunotherapy will need to be compared to the PACIFIC regimen in a larger randomized trial. Clinical trial information: NCT02525757