1429P Pathological regression in patients with microsatellite instability (MSI) receiving perioperative atezolizumab in combination with FLOT vs. FLOT alone for resectable esophagogastric adenocarcinoma: Results from the DANTE trial of the German Gastric Group at the AIO and SAKK

Abstract

There is a debate about whether patients (pts) with MSI should receive neoadjuvant chemotherapy. DANTE evaluates perioperative FLOT vs. FLOT/atezolizumab for resectable gastric or GEJ adenocarcinoma. Here, we report preliminary data for the pathological (path) regression in pts with MSI. DANTE is a bi-national, multicenter, investigator-initiated, phase IIb trial. Pts with resectable adenocarcinoma of the stomach and GEJ (≥cT2 and/or N+) were randomized to either receive 4+4 cycles of periop. FLOT q2w or 4+4 cycles of periop. FLOT + atezolizumab at 840 mg q2w followed by atezolizumab monotherapy for 8 cycles at 1200 mg q3w. MSI and path regression (Becker-Classification) have been centrally evaluated in 195 pts, so far. By Oct 2020, the trial was fully recruited with 295 pts. Median age was 61y, with 74% male pts. 42% of pts had an intestinal type acc. to Laurén and 61% had GEJ adenocarcinoma. Overall, 22 pts (7%) were assessed MSI. Rate of path complete regression (TRG1a) was higher in pts with MSI than those with MSS (10/22 pts [46%] vs. 41/173 pts [24%]). Among MSI pts, rates of path complete or subtotal regression (TRG1a/b) were 80% (8/10) after FLOT/atezolizumab vs. 59% (7/12) after FLOT.Table: 1429PPath regression by MSI status and treatment armMSI (n=22)Path regressionFLOT n=12Atezo/FLOT n=10Complete (pCR/TRG1a)5 (42%)5 (50%)Subtotal (pSR/TRG1b)2 (17%)3 (30%)Partial (PR/TRG2)1 (8%)1 (10%)Minor or no regression4 (33%)1 (10%) Open table in a new tab Pts with MSI generally achieved very high rates of path regression following FLOT or FLOT/atezolizumab. Contrary to previous retrospective studies, our study supports offering perioperative therapy to pts with MSI and gastric and GEJ adenocarcinoma.