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Background LCMC3 (NCT02927301), an open-label, single-arm Phase 2 study to investigate neoadjuvant (neoadj) and adj atezo (anti-PD-L1) in patients (pts) with early-stage non-small cell lung cancer (NSCLC), met its primary endpoint with a 20% major pathological response (MPR) rate after neoadj atezo. Here we report efficacy and safety from the adj phase. Methods Eligible pts aged ≥18 y had resectable stage IB-IIIA or select IIIB NSCLC and ECOG PS of 0 or 1. Pts received neoadj atezo 1200 mg IV for ≤2 cycles (Days 1 and 22) followed by surgery (Day 40±10). Pts deemed to have clinical benefit were offered the option to receive adj atezo every 3 weeks for up to 12 months. The primary endpoint was MPR rate (≤10% viable tumor cells at surgery) in pts without EGFR/ALK mutations. Exploratory endpoints included DFS and OS. Safety was assessed during the adj phase. Results Data cutoff was Oct 21, 2022. The primary efficacy population (PEP) was 137 pts without EGFR/ALK alterations who had surgery and MPR assessment. In the PEP, 53 pts (39%) received adj atezo and 84 (61%) did not. The 3-y DFS rate was 83% with adj atezo vs 64% without (HR, 0.43; 95% CI: 0.21, 0.90; P=0.025). 3-y OS and results by MPR status are provided in the table. In the adj atezo safety population (n=57), treatment-related (TR) AEs after adj atezo occurred in 55 pts (97%; Gr 3/4, 40%), including 11 TRAEs (19%; Gr 3/4, 16%) leading to discontinuation of adj atezo. No Gr 5 TRAEs were seen in the adj phase. Multivariate analysis also showed a trend toward better DFS for pts receiving adj atezo vs those with no adj atezo (HR, 0.52; 95% CI: 0.22, 1.21; P=0.126). Conclusions This exploratory analysis revealed that LCMC3 pts with resectable stage IB-IIIA or select IIIB NSCLC who received adj atezo had improved DFS and showed a trend toward improved OS vs pts who did not receive adj atezo. Furthermore, the non-MPR subgroup had the same trend toward improved DFS and OS with adj atezo vs pts who did not receive adj atezo. Adj atezo was well tolerated, with no new safety concerns. Table Adj atezoa n=53 No adj atezob n=84 Tx patterns Adj atezo + adj chemo, n (%) 17 (32) 0 Adj atezo, n (%) 36 (68) 0 Adj chemo, n (%) 0 36 (43) None, n (%) 0 48 (57) Tx cycles Adj atezo, n, median (range) 53, 16 (1-18) 0 Adj chemo, n, median (range) 16, 3 (0-4.2) 35, 3 (0-4.1) HR (95% CI) P PEP (N=137) 3-y DFS, % 83 64 0.43 (0.21, 0.90) 0.025 3-y OS, % 89 77 0.48 (0.19, 1.21) 0.118 MPR (n=29) n=22 n=7 3-y DFS, % 86 86 0.93 (0.10, 8.92) 0.948 Non-MPR (n=108) n=31 n=77 3-y DFS, % 80 62 0.48 (0.20, 1.12) 0.088 3-y OS, % 87 75 0.49 (0.17, 1.46) 0.202 Multivariable Cox regression (n=114)c MPR vs non-MPR 0.37 (0.11, 1.31) 0.125 Adj atezo vs no adj atezo 0.52 (0.22, 1.21) 0.126 Adj chemo vs no adj chemo 0.57 (0.27, 1.19) 0.133 Stage I/II vs III 0.71 (0.35, 1.43) 0.338 PD-L1 tumor proportion score ≥1% vs Citation Format: David Paul Carbone, Saiama N. Waqar, Jamie E. Chaft, Mark G. Kris, Bruce E. Johnson, Jay M. Lee, Ignacio I. Wistuba, David Kwiatkowski, Paul Bunn, Katja Schulze, Ann Johnson, Evelise Brandao, Mark Awad, Karen L. Reckamp, Anne C. Chiang, Alan Nicholas, Valerie Rusch. Efficacy and safety of adjuvant (adj) atezolizumab (atezo) from the Phase 2 LCMC3 study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT215.