A Study to Evaluate the Effect of Repeat Oral Dosing of GSK2118436 on Cardiac Repolarization in Subjects With V600 BRAF Mutation-Positive Tumors

This is a Phase I, multicenter, 2-part study with Part 1 designed as a safety lead-in and Part 2 designed to evaluate the effect of GSK2118436 on cardiac repolarization (corrected QT interval \[QTc\] duration) as compared with placebo in subjects with V600 BRAF mutation-positive tumors. Each part of the study will consist of screening (14 days prior to the start of the study treatment), treatment and follow-up period (14 days). In Part 1 in Cohort 1 six subjects will receive GSK2118436 225 mg twice a day (BID) on study days 1 to 7 and a single 225 milligram (mg) dose on morning of Day 8. Based on the safety data of subjects in Cohort 1 subjects will be enrolled in Cohort 2 and the dose of GSK2118436 will be escalated to 300 mg BID. If the 225 mg dose of GSK2118436 is not well tolerated in Cohort 1 (i.e., 2 or more dose-limiting toxicities \[DLTs\]), then Cohort 2 of Part 1 will not be initiated and a dose of 150 mg BID of GSK2118436 will be administered in Part 2 of the study. In Cohort 2 six subjects will receive GSK2118436 300 mg BID on Study Days 1 to 7 and a single 300 mg dose on the morning of Day 8. Based on the safety data of subjects in Cohort 2 subjects will be enrolled in Part 2. If the 300 mg BID dose level of GSK2118436 is not well tolerated, then the highest tolerated dose will be selected for Part 2 of the study. In Part 1 of the study the decision to proceed to the next cohort or Part 2 of the study will be based on the safety data of at least 6 evaluable subjects (\<=1 DLTs during the 14 days following the first dose of GSK2118436). In Part 2 of the study eligible subjects will receive a single dose of GSK2118436/placebo (4 capsules of 75 mg/highest tolerated dose) orally on the first 2 days of the study followed by 2 doses daily for 6 days and a single dose on the 9th day. There will be 1 day when a placebo will be given. In both the parts of the study serial blood samples for pharmacokinetic (PK) analysis for GSK2118436 and its metabolites (GS