Perioperative Atezolizumab Plus Fluorouracil, Leucovorin, Oxaliplatin, and Docetaxel for Resectable Esophagogastric Cancer: Interim Results From the Randomized, Multicenter, Phase II/III DANTE/IKF-s633 Trial.

PURPOSE This trial evaluates the addition of the PD-L1 antibody atezolizumab (ATZ) to standard-of-care fluorouracil, leucovorin, oxaliplatin, and docetaxel (FLOT) as a perioperative treatment for patients with resectable esophagogastric adenocarcinoma (EGA). METHODS DANTE started as multicenter, randomized phase II trial, which was subsequently converted to a phase III trial. Here, we present the results of the phase II proportion, focusing on surgical pathology and safety outcomes on an exploratory basis. Patients with resectable EGA (≥cT2 or cN+) were assigned to either four preoperative and postoperative cycles of FLOT combined with ATZ, followed by eight cycles of ATZ maintenance (arm A) or FLOT alone (arm B). RESULTS Two hundred ninety-five patients were randomly assigned (A, 146; B, 149) with balanced baseline characteristics between arms. Twenty-three patients (8%) had tumors with microsatellite instability (MSI), and 58% patients had tumors with a PD-L1 combined positive score (CPS) of ≥1. Surgical morbidity (A, 45%; B, 42%) and 60-day mortality (A, 3%; B, 2%) were comparable between arms. Downstaging favored arm A versus arm B (ypT0, 23% <i>v</i> 15% [one-sided <i>P</i> = .044]; ypT0-T2, 61% <i>v</i> 48% [one-sided <i>P</i> = .015]; ypN0, 68% <i>v</i> 54% [one-sided <i>P</i> = .012]). Histopathologic complete regression rates (pathologic complete response or TRG1a) were higher after FLOT plus ATZ (A, 24%; B, 15%; one-sided <i>P</i> = .032), and the difference was more pronounced in the PD-L1 CPS ≥10 (A, 33%; B, 12%) and MSI (A, 63%; B, 27%) subpopulations. Complete margin-free (R0) resection rates were relatively high in both arms (A, 96%; B, 95%). The incidence and severity of adverse events were similar in both groups. CONCLUSION Within the limitations of the exploratory nature of the data, the addition of ATZ to perioperative FLOT is safe and improved postoperative stage and histopathologic regression.