This is a multinational, double-blind, two-arm, parallel, randomized, Phase 3 study evaluating the efficacy and safety of TAS-102 plus BSC versus placebo plus BSC in patients with metastatic gastric cancer who have previously received at least 2 prior regimens for advanced disease. Eligible patients will be centrally randomized (2:1) to TAS-102 + BSC (experimental arm) or placebo + BSC (control arm).