GSK1120212 is an orally administered, potent and highly selective small molecule inhibitor of MEK1(mitogen-activated extracellular signal-regulated kinase-1)/MEK2 (mitogen-activated extracellular signal-regulated kinase-2) activation and kinase activity. As monotherapy, GSK1120212 has shown an acceptable risk-benefit profile with encouraging efficacy in various oncologic settings. This Phase I, single-sequence, placebo-controlled, singleblind, multicenter study is designed to evaluate the effects of repeat oral dosing of GSK1120212 on electrocardiographic parameters with a particular focus on its effect on cardiac repolarization (Corrected QT interval [QTc] duration) as compared to placebo in subjects with solid tumor cancers. A single dose of placebo will be administered on Study Day 1 followed by administration of a once-daily 2 mg dose of GSK1120212 for 13 days (Study Days 2 through 14) and on Study Day 15 a dose of 3 mg of GSK1120212 will be given. Digital 12-lead electrocardiograms (ECGs) will be extracted from continuous ECG recordings obtained via Holter monitor on Study Days 1 and 2 after the administration of placebo and on Study Days 15 and 16 after the administration of GSK1120212. Pharmacokinetic samples will be time-matched with the Holter ECGs. This study will also assess the exposure-QTc relationship between plasma concentrations of GSK1120212 and its effect, if any, on cardiac repolarization, specifically on the QTc interval. Continuous 24-hour ambulatory blood pressure monitoring will be conducted to assess the effect of GSK1120212 on blood pressure parameters on Study Days 1 and 15. Safety assessments, including assessment of adverse events, clinical laboratory tests (hematology and clinical chemistry) and vital signs, will be performed throughout the study. Following completion of study treatment, eligible subjects may transition to the open-label, rollover study MEK114375 to continue treatment with GSK1120212.