Maintenance durvalumab after first-line platinum-based chemotherapy in advanced oesophago-gastric (OG) adenocarcinoma: Results from the PLATFORM trial

Abstract

Background: PLATFORM is a prospective, open-label, multicentre, adaptive phase II trial assessing maintenance therapy in patients (pts) with OG adenocarcinoma after platinum-based first-line induction chemotherapy. HER2 negative pts were initially randomised 1:1:1:1:1 to surveillance (A1), capecitabine (A2), durvalumab (A3), with rucaparib (A4) and capecitabine + ramucirumab (A5) added later as per adaptive design. Here we report the primary analysis of durvalumab maintenance vs. surveillance. Methods: Pts were randomised upon achieving response or stable disease following 18 weeks of platinum-based chemotherapy and were stratified by region, disease extent and performance status. A1 pts had 4 weekly surveillance visits and A3 pts received 10mg/kg durvalumab iv Q2W. Target accrual was 154 pts/arm; however, A3 was closed prematurely after cessation of industry support. The primary endpoint was progression-free survival (PFS) from randomisation post induction chemotherapy to disease progression according to RECIST 1.1 criteria, or death. Secondary endpoints were time to treatment failure (TTF), objective response rate (ORR), overall survival (OS) and toxicity. Survival analyses according to PD-L1 using the combined positive score (CPS, Ventana SP263 assay) was conducted. Results: A total of 205 pts were concurrently randomised into A1 (n = 100) and A3 (n = 105). At data cut-off (02 Feb 2021), median follow up was 24.2 months [95% confidence interval (CI) 21.6-36.8]. There was no significant difference in PFS between A1 and A3 [median PFS: 3.2 vs. 4.7 months (hazard ratio (HR) 0.79 (95% CI 0.59-1.06, p = 0.122) respectively]. Median OS was 11.4 vs. 11.3 months (HR 0.92, 95% CI 0.66-1.27, p = 0.60) in A1 and A3 respectively and no significant difference in TTF was detected between both arms (median TTF: 3.2 vs. 3.5 months (HR 0.92, 95% CI 0.69-1.23, p = 0.558)]. ORR was 6% in A3 (n = 2 complete and n = 4 partial responses) whereas no radiological responses were seen in A1. PD-L1 results were available for 76 pts in A1 and 77 pts in A3. PFS was comparable between subgroups using the PD-L1 CPS thresholds of ≥1, ≥5 and ≥10. The safety population consisted of 199 pts (A1: 98 pts and A3: 101 pts). Grade ≥3 treatment-related adverse events were reported in 18% of A3 pts and no new safety signals were identified. Conclusions: Although a survival advantage was not seen with maintenance durvalumab compared to surveillance, a subset of patients who received durvalumab demonstrated incremental radiological responses. Exploratory analysis of PD-L1 expression was not associated with improved survival outcomes.