Olaparib plus paclitaxel sensitivity in biomarker subgroups of gastric cancer

Abstract

Background: Study 39 (NCT01063517) showed a significant improvement in overall survival (OS) following olaparib plus paclitaxel (OP) vs paclitaxel (P) alone in advanced gastric cancer, with improvements greatest in patients (pts) with low or undetectable tumour ATM protein levels. The Phase III GOLD study (NCT01924533) also showed a survival benefit trend for OP vs P. We investigated biomarker subgroups, candidate genes and homologous recombination repair (HRR) deficiency using predefined and post-hoc exploratory analyses, to determine if a predictive relationship exists between such biomarkers and clinical outcome in gastric cancer pts treated with OP. Methods: Candidate genes, HRR deficiencies, loss of heterozygosity (LoH) and microsatellite insufficiency (MSI) were assessed in formalin-fixed, paraffin-embedded gastric tumour samples from GOLD by next-generation sequencing. HRR deficiencies were identified as carrying pathogenic mutations in any 15 HRR genes and LoHusing allelespecific copy number information coupled with assessed tumour purity. ATM protein level was assessed by immunohistochemistry (IHC). Clinical outcomes analyzed were OS, PFS and ORR. Results: Efficacy in the genetics evaluable population (n=400) was broadly consistent with the overall GOLD population (n=525) for each outcome investigated. ATM-negative patients by IHC had better prognosis independent of treatment. No statistically significant associations with clinical outcomes were identified (Table). Post-hoc exploratory analyses indicated good prognosis (OS) in pts with an ATM mutation, and poor prognosis in pts with CDH1, FGFR2 or KRAS mutations. Conclusions: None of the pre-specified molecular subgroups had a better outcome from adding olaparib to paclitaxel than the overall GOLD population. Additional studies are required to understand the OS signal observed with OP treatment in pts with advanced gastric cancer in the GOLD study. Yu-Zhen Liu and Darren Hodgson are joint first authors. (Table Presented) .