221P - Evaluation of Met Staining in Gastric/Gastroesophageal Junction (G/Gej) Tumor Samples As a Biomarker for Rilotumumab (R) Benefit

Abstract

ABSTRACT Aim: R is an investigational, fully human monoclonal antibody against hepatocyte growth factor, the only known ligand for the MET proto-oncogene. In a phase 2 study in G/GEJ cancer, trends towards improved overall survival (OS) and progression-free survival (PFS) were seen with R + epirubicin, cisplatin, and capecitabine (ECX) vs placebo + ECX, with benefit due to the MET-positive patients (pts). We describe a methodology to select a cutoff for defining MET positivity. Methods: Eligible pts had unresectable locally advanced or metastatic G/GEJ adenocarcinoma, ECOG performance status ≤ 1, and no prior systemic therapy for this disease. Pts were randomized 1:1:1 to R 15 mg/kg, R 7.5 mg/kg, or placebo IV day 1 Q3W plus ECX (50 mg/m2 IV day 1, 60 mg/m2 IV day 1, 625 mg/m2 BID orally days 1–21, respectively). Formalin-fixed paraffin-embedded archival tumor tissues were stained with the Dako MET IHC pharmDx™ kit, which uses the MET4 antibody. Membrane, cytoplasmic, and total (cytoplasmic and membrane) tumor cell staining were evaluated separately. Percent staining at different intensities (0, 1 + , 2 + , 3+) and combinations of intensities were scored directly, whereas overall percent positive, H-score, and predominant staining intensity were derived scores. OS and PFS for subgroups defined by potential cutoff values (5–95%) at 5% increments were analyzed by Cox proportional hazards regression, Kaplan-Meier, and the log rank test, yielding hazard ratios (HRs), median OS and PFS, and p values. Results: 121 pts were randomized; 91 had tumor samples evaluable for MET IHC. Pts whose tumors showed ≥ 25% membranous staining were classified as MET-positive. A strong treatment benefit (R vs placebo) was seen in MET-positive pts (n = 58; OS: HR = 0.46, 95% CI, 0.24–0.87; PFS: HR = 0.46, 95% CI, 0.25–0.85); median OS: 10.6 vs 5.7 mo; median PFS: 6.8 vs 4.4 mo. No benefit or detriment was seen with R in MET-negative pts (n = 33; OS: HR = 1.23; 95% CI, 0.56–2.70; PFS: HR = 1.00; 95% CI, 0.46–2.16). Cutoff values 25–50% showed a similar benefit of R in MET-positive pts. Conclusions: The subgroup defined by a cutoff of 25% MET-positive membranous staining using the Dako MET IHC pharmDx™ kit showed benefit from R + ECX; no negative impact of R was seen in MET-negative pts. This cutoff is being used to select pts in an ongoing phase 3 study of R + ECX in MET-positive G/GEJ cancer (NCT01697072). Disclosure: M.D. Hale, K.S. Oliner, R. Tang, L. Chen, E. Loh and S.D. Patterson have declared:is an employee of and owns stock in Amgen Inc.; S. Webster: Scott Webster is an employee of Dako North America, an Agilent Technologies Company. All other authors have declared no conflicts of interest.