A Randomized Phase 2 Trial of TAS-114 in Combination With S-1 Versus S-1

Randomization will take place once the consented patient has completed all the necessary baseline procedures and is deemed eligible for study entry. Treatment assignment will be done centrally using a dynamic allocation method (biased coin) via an interactive voice/web response system (IXRS) stratified by: * Geographical region (Region 1: Asian \[Japan\]; Region 2: Western \[Europe and US\]) * Histological subtypes (nonsquamous cell carcinoma \[including mixed\] and squamous cell carcinoma)