Exposure-Response Analyses of Ramucirumab from Two Randomized, Phase III Trials of Second-line Treatment for Advanced Gastric or Gastroesophageal Junction Cancer

Ramucirumab is an IgG₁ monoclonal antibody specific for the vascular endothelial growth factor receptor-2. Ramucirumab, 8 mg/kg every 2 weeks, administered as monotherapy (REGARD) or in combination with paclitaxel (RAINBOW), was safe and effective in patients with previously treated advanced gastric or gastroesophageal junction (GEJ) cancer. We evaluated exposure-efficacy and exposure-safety relationships of ramucirumab from two randomized, placebo-controlled phase III trials. Sparse pharmacokinetic samples were collected, and a population pharmacokinetic analysis was conducted to predict ramucirumab minimum trough concentration at steady state (C_min,ss). Kaplan-Meier methods and Cox proportional hazards models were used to evaluate the ramucirumab exposure (C_min,ss)-efficacy relationship to overall survival (OS) and progression-free survival (PFS). Logistic regression analyses were used to evaluate exposure-safety relationships. Analyses included 321 ramucirumab + paclitaxel and 335 placebo + paclitaxel patients from RAINBOW and 72 ramucirumab and 35 placebo patients from REGARD. Exposure-efficacy analysis showed ramucirumab C_min,ss was a significant predictor of OS and PFS in both trials. Higher ramucirumab exposure was associated with longer OS and PFS. In RAINBOW, grade ≥3 hypertension, leukopenia, and neutropenia, but not febrile neutropenia, significantly correlated with C_min,ss, with increased exposure leading to increased incidence. Exploratory exposure-response analyses suggest a positive relationship between efficacy and ramucirumab exposure with manageable toxicities at exposures generated from a dose of 8 mg/kg ramucirumab given every 2 weeks for patients with advanced gastric/GEJ cancer. These findings suggest an opportunity to further optimize benefit versus risk profiles of ramucirumab treatment in patients with gastric/GEJ cancer. <i>Mol Cancer Ther; 16(10); 2215-22. ©2017 AACR</i>.