45P Alofanib in Subsequent Therapy of Advanced Gastric Cancer: Final Results from the Phase Ib Clinical Trial

e16077 Background: Alofanib (RPT835) is a first-in-class allosteric inhibitor that induces conformational changes in the extracellular domain of FGFR2. Here, we present the final results of the phase Ib clinical study (RPT835GC1B) of alofanib. Methods: Patients with metastatic gastric adenocarcinoma resistant to standard therapy with measurable disease were eligible. The dose finding part used a 3+3 design, starting with a dose level of 50 mg/m2, intravenously, 5 days on, 2 days off. Five dose levels were foreseen. Primary endpoint was maximum tolerated dose (MTD). Secondary endpoints included toxicity, PK, objective response rate (ORR), overall survival (OS), and progression-free survival (PFS). Results: 21 patients were enrolled. 4 (19.1%), 14 (66.7%), 9 (43%), 3 (14.3%), and 12 (57%) patients had ECOG PS 2, ≥2 metastatic sites, liver metastases, bone metastases, and 3-6 lines previous therapy, respectively. The MTD has not been reached and dose of 350 mg/m2 has been declared as recommended phase II dose. With median follow-up of 13.0 months 15 (71.4%) patients had any grade treatment related adverse events (TRAE). Grade 3-4 TRAE occurred in 6 (28.6%) patients. Two (9.5%) patients discontinued treatment due to grade 3 diarrhea and grade 4 reactions immediately after injections. There were no treatment-related deaths in the study. One partial response (5.26%) with a duration of 18.53 months was identified. Disease control rate (DCR) was 68.4% and median duration of stable disease was 4.91 months. Median PFS was 3.63 (95% CI 1.58–5.68) months. Median OS was 7.0 (3.82–10.18) months. 6-month OS rate was 57.1%. OS was almost 2 times better in patients with DCR (median 10.05 vs. 5.9 months) and without bone metastases (8.6 vs. 3.1). Only one patient (4.8%) had FGFR2 amplification (time to death was 7 months). PK parameters linearly changed depending on the dose level, but no correlation with efficacy was found. Table summarizes rate of TRAE and DCR in dose cohorts. Conclusions: Alofanib was feasible and showed early signals of efficacy in heavily-pretreated patients with metastatic gastric cancer. A phase 2 randomized trial is planned. Clinical trial information: NCT04071184. [Table: see text]