Evaluating maintenance therapies in advanced oesophago-gastric adenocarcinoma (OGA): Interim analysis and biomarker results from the PLATFORM study.

Abstract

282 Background: Advanced OGA patients (pts) are treated with platinum-based 1st line chemotherapy but the role of maintenance therapy once disease control is obtained is unknown. Methods: PLATFORM is a prospective, open-label, adaptive phase II trial assessing maintenance therapy in OGA. HER2 negative pts with advanced OGA achieving response or stable disease on completion of 1st line platinum-based chemotherapy were initially randomised to surveillance (A1), capecitabine (A2) and durvalumab (A3). Rucaparib (A4) and capecitabine+ramucirumab (A5) were subsequently added as part of adaptive design. Primary endpoint is progression-free survival with target recruitment of 154pts/arm. A pre-planned futility interim analysis (IA) is triggered when 61 pts/arm are recruited and evaluable using 12-week progression-free rate (PFR). Individual arms will continue accrual if the upper limit of 1-sided 95% CI difference is > 0 when compared to A1. Biomarker analyses of A1 and A3 IA patients include: PDL1 as tumour and immune cell combined proportion (TIP), multiplex IHC of tumour infiltrating lymphocytes (TILs), TMB and MSI status by whole exome sequencing. Results: To date, 1053 pts have registered prior to or during 1st line therapy and 356 pts randomised. Primary attrition was due to disease progression. Baseline demographics in the IA population (arms A1 to A3, n = 183) were male (81%); median age 65 yrs; metastatic disease (92%); oesophageal (40%), OG junction (28%) and gastric (32%) primary. 12-week PFR were A1: 51% (95%CI: 38-64%); A2: 52% (95%CI: 40-65%); A3: 49% (95%CI: 36-62%). PFR differences to arm A1 were A2: 1.6% (95%CI: -13.2 to 16.5%); A3: -1.6% (95%CI: -16.5 to 13.3%). In A1, PFR was 53% vs 43% in PDL1 TIP < 10% and ≥10% respectively. In A3, PFR was 51% vs 100% in PDL1 TIP < 10% and ≥10% respectively. 3 pts in A3 had partial response; none were seen in A1 and A2. Density of TILs subsets, TMB and MSI data will be presented. Conclusions: PLATFORM IA did not indicate futility in maintenance capecitabine or durvalumab compared to surveillance in advanced OGA and will continue to target accrual. Incremental radiological responses were observed with maintenance durvalumab only. Clinical trial information: NCT02678182.