Background: FLOT was established as a perioperative therapy for GC/GEJC following the Phase 2/3 FLOT4 study conducted in Germany, with a pCR rate of 16% (Al-Batran et al, Lancet Oncol 2016). The global MATTERHORN study (NCT04592913) showed a statistically significant improvement in pCR with perioperative D + FLOT vs placebo (P) + FLOT in GC/GEJC at first interim analysis (Janjigian et al, ESMO Congress 2023). Subgroup analyses by region and country were completed to assess pCR rates with FLOT and benefit of D + FLOT across the global study population. Methods: Participants (pts) with resectable GC/GEJC were randomized 1:1 to D 1500 mg or P every 4 weeks (Q4W) on Day 1 plus FLOT Q2W on Days 1 and 15 for 4 cycles (2 doses of D or P and 4 doses of FLOT pre- and post-operative), followed by D 1500 mg or P on Day 1 Q4W for 10 further cycles. Randomization was stratified by Asia vs non-Asia. pCR (Modified Ryan; central review) was assessed in prespecified (Asia) and post hoc regional subgroups, including 6 countries with the highest numbers of randomized pts. Results: Of 948 pts randomized globally, 180 pts (19%) were in Asia. pCR outcomes with FLOT in Asia were consistent with the global outcomes. pCR rates were improved with D + FLOT vs P + FLOT in all regions (Asia, Europe, North America and South America; Table), despite some imbalances in baseline characteristics and numerical differences in pCR rates by geographic location. The pCR rate with P + FLOT in the German subgroup (13%; 95% CI, 6.1–23.0) was similar to that with FLOT in the FLOT4 study. Improvement in pCR with D + FLOT vs P + FLOT was observed across subgroups by country. Similar trends across regional subgroups were observed for combined complete and near-complete response rate. Conclusions: In MATTERHORN, pCR was consistently improved with the addition of D to perioperative FLOT in GC/GEJC across geographic regions. The study is ongoing for the primary objective of event-free survival. Clinical trial information: NCT04592913.