Background: T-DXd is an antibody-drug conjugate comprising an anti-HER2 antibody, a cleavable tetrapeptide-based linker, and a topoisomerase I inhibitor. DESTINY-Gastric01 (DS8201-A-J202; ClinicalTrials.gov, NCT03329690) is an open-label, multicenter, randomized, phase 2 trial of T-DXd in patients with HER2–positive advanced gastric cancer (GC) or GEJ adenocarcinoma. In the primary analysis (101 OS events; median survival follow-up, 12.3 mo), T-DXd showed statistically significant benefit vs standard chemotherapy in objective response rate (ORR) and OS (Shitara K, et al. N Engl J Med. 2020;382:2419-2430); here, we present the final OS analysis as well as updated efficacy and safety. Methods: Patients (pts) with locally advanced or metastatic, centrally confirmed HER2–positive (IHC3+ or IHC2+/ISH+ on archival tissue) GC or GEJ cancer that had progressed after ≥2 previous lines of therapy including trastuzumab were randomly assigned 2:1 (T-DXd 6.4 mg/kg Q3W or physician’s choice [PC] of irinotecan [I] or paclitaxel [P]). Pts were stratified by country, ECOG performance status (0, 1), and HER2 status. Primary endpoint was ORR by independent central review. Key secondary endpoints were OS, duration of response (DOR), progression-free survival (PFS), disease control rate (DCR), confirmed ORR, and safety. Final OS analysis was performed at 133 OS events. Results: 187 pts received T-DXd (n = 125) or PC (n = 62 [55 I; 7 P]); 79.7% of pts were Japanese and 20.3% were Korean. Pts had a median of 2 prior lines of therapy, and 44.4% had ≥3. At data cutoff (June 3, 2020), 8% of T-DXd and 0% of PC pts remained on treatment (median survival follow-up, 18.5 mo). OS was improved with T-DXd vs PC (median OS, 12.5 vs 8.9 mo; hazard ratio [HR], 0.60 [95% CI, 0.42-0.86]); 12-month OS, 52.2% vs 29.7%. ORR was 51.3% (61/119; 11 CR; 50 PR) with T-DXd vs 14.3% (8/56; all PR) with PC (P< 0.0001); confirmed ORR, 42.0% (50/119; 10 CR; 40 PR) vs 12.5% (7/56; all PR) (P= 0.0001); DCR, 85.7% vs 62.5% (P= 0.0005); confirmed median DOR, 12.5 vs 3.9 mo; median PFS, 5.6 vs 3.5 mo (HR, 0.47 [95% CI, 0.31-0.71]; P= 0.0003). Grade ≥3 AEs occurred in 85.6% of T-DXd pts vs 56.5% with PC; the most common were neutrophil count decreased (51.2%, 24.2%), anemia (38.4%, 22.6%), and white blood cell count decreased (20.8%, 11.3%). 16 pts (12.8%) had T-DXd–related interstitial lung disease (ILD; 13 grade 1/2, 2 grade 3, 1 grade 4, no grade 5) vs 0 with PC. As reported in the primary analysis, there was 1 T-DXd–related death from pneumonia (non-ILD). Conclusions: With additional follow-up after the primary analysis, T-DXd continued to demonstrate OS benefit and clinically relevant improvement in ORR compared with standard chemotherapy, and a manageable safety profile, in HER2–positive advanced GC or GEJ adenocarcinoma. Clinical trial information: NCT03329690.