Background: Several options have been evaluated as 2^nd line treatment in mGA after failure of 1^st line platinum based chemotherapy including taxanes and IRI as monotherapies or paclitaxel combined with ramucirumab but with a limited efficacy. REG monotherapy showed promising efficacy as 2^nd or 3^rd line treatment in mGA (Pavlakis N et al, J Clin Oncol. 2016). Methods: This comparative phase 2 multicenter randomized study was designed to evaluate the safety and efficacy of REG + IRI (REGIRI) vs IRI alone as 2^nd line treatment in MGA patients (pts). Key eligibility criteria were histologically proven mGA (gastric or gastroesophageal junction (GEJ) tumor Siewert II and III), fluoropyrimidine and platinum-based first-line chemotherapy and ECOG PS ≤1. Pts received IRI 180 mg/m² IV on D1 and D15. In REGIRI arm REG 160 mg/day was added on D2-D8 and D16-D22 every 28 days. Primary endpoint was overall survival (OS). A total of 122 events (154 pts) were required based on an assumption of 4-month (mo) gain in median OS (from 6 to 10 mo, HR=0.60), with a preplanned interim analysis of safety after 38 pts and efficacy after 40 OS events. Genotyping of cyclin-D1 was performed to evaluate the impact of treatment efficacy. Results: A total of 89 patients (REGIRI, n=44; IRI, n=45) with median age of 62 (range: 28-82) years and a mGA (67.4% with GEJ, 22.8% HER2+) were included out of the 154 initially planned by 21 sites in France. Study was prematurely stopped after interim analysis for unfavourable efficacy/toxicity ratio. With a median follow-up of 19.4 mo, 79 OS events were observed and median OS was 6.3 mo (95%CI[5.2-7.1]) with REGIRI vs 8.2 mo (95%CI[5.2-9.7]) with IRI (HR=1.11 CI95%[0.70-1.74], p=0.66). Median PFS was 2.2 mo vs 1.9 mo (NS) with REGIRI and IRI, respectively. Objective response rate was 15.9% and 13.3% respectively. Disease control rate was 45.5% and 33.3%. AEs grade ≥ 3 related to treatment were reported in 52.3% of pts in REGIRI arm vs 23.3% in IRI arm with 4 toxic deaths (diarrhea, sepsis and thromboembolic events) vs 1 (primary tumour perforation), respectively. The main severe toxicities were diarrhea: 18.2% vs 7% and febrile neutropenia: 8.2% vs 0%. Genotyping of cyclin D1 was performed on 72 pts: 19 presented A/A genotype, 38 A/G and 15 G/G. There were no differences in terms of OS according to genotyping. Conclusions: PRODIGE58/REGIRI trial was prematurely stopped after the interim analysis due to high toxicities reported in REGIRI arm with negative results on its primary endpoint. Further ancillary analysis are expected to identify toxicity risk factors and pts subgroups benefit with this combination. Clinical trial information: NCT03722108.