Final Overall Survival (Os) Analysis With Modeling Of Crossover Impact In The Phase Iii Grid Trial Of Regorafenib Vs Placebo In Advanced Gastrointestinal Stromal Tumors (Gist).

156 Background: GRID showed that regorafenib (REG) improves progression-free survival (PFS; primary endpoint) vs placebo (PBO) in patients (pts) with advanced GIST after failure of at least imatinib and sunitinib (HR 0.27; 1-sided p u003c 0.0001). An interim OS analysis at the time of the primary PFS analysis showed a positive trend (HR 0.77; p = 0.199) despite 85% of PBO pts crossing over to REG. An exploratory analysis modeling the impact of crossover on OS suggested a benefit for REG. We present exploratory analyses of OS comparing crossover correction results at different times, including at the planned final OS analysis. Methods: Data cut-off dates for OS analyses were 26 Jan 2012 (final PFS analysis), 31 Jan 2014, and 8 Jun 2015 (final OS analysis). The impact of crossover on OS was modeled using 2 randomization-based methods: rank preserving structural failure time (RPSFT) and iterative parameter estimation (IPE), both considered best choice among correction analytics. Hazard ratios (HRs) and 95% CIs w...