BRAF/MEK/EGFR Inhibitor Combination Study in Colorectal Cancer (CRC)

Inclusion Criteria: Subjects eligible for enrolment in this study must meet all of the following criteria

• Provided written informed consent,
• Male or female >=18 years of age and able to swallow and retain orally administered study treatment and does not have any clinically significant gastrointestinal (GI) abnormalities that may alter absorption such as malabsorption syndrome or major resection of the stomach and/or bowels.
• Part 1 and Part 2: Histologically- or cytologically-confirmed diagnosis of advanced or metastatic BRAF V600E mutation positive CRC
• Part 4A and 4B ONLY: Histologically- or cytologically-confirmed diagnosis of advanced or metastatic CRC that either harbours the BRAF V600E -mutation, as determined by relevant genetic testing OR has developed secondary resistance to anti-EGFR therapy, defined as patients that derived benefit (disease control based on investigator assessment for >6 months OR partial response [confirmed or unconfirmed] based on RECIST 1.1) from prior anti-EGFR-containing therapy (as defined below) and then subsequently progressed on therapy. The anti-EGFR therapy must have been the most recent therapy and the patient must have progressed based on investigator assessment within 3 months of screening. Acceptable prior anti-EGFR-containing therapies include: a. Monotherapy anti-EGFR, including cetuximab or panitumumab OR b. irinotecan/anti-EGFR combo after previously having disease progression (based on investigator assessment) on an irinotecan-containing regimen
• Part 3: Histologically- or cytologically-confirmed diagnosis of BRAFV600E mutation positive advanced or metastatic colorectal cancer (CRC who are eligible to receive fluoropyrimidine-containing chemotherapy regimen that have experienced documented radiographic progression on one prior line of fluoropyrimidine-containing chemotherapy (previous anti-EGFR therapy is excluded), Second-line for advanced/metastatic disease, having failed or been intolerant to at least one regimen of fluoropyrimidine-containing chemotherapy including irinotecan or oxaliplatin in the advanced/metastatic setting. Enrollment in Part 3 may only occur following confirmation of KRAS wild-type cancer.
• Archival tissue is required; if archival tissue is not available or found to not contain tumor tissue, a fresh biopsy is required.
• Measurable disease per RECIST version 1.1.
• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.
• Men with a female partner of childbearing potential must have either had a prior vasectomy or agree to use one of the contraception methods listed in protocol.
• Female subjects are eligible if: Non-childbearing potential defined as pre-menopausal females with a documented tubal ligation or hysterectomy; or post-menopausal female defined as 12 months of spontaneous amenorrhea to be verified with a follicle-stimulating hormone (FSH) level >40 Milli-international units per milliliter (MIU/mL) and estradiol level =90 days prior to first dose of study drug(s). This must be documented with two consecutive MRI or CT scans using contrast, and Asymptomatic with no corticosteroids requirement for >=30 days prior to first dose of study drug(s), and No enzyme-inducing anticonvulsants for >=14 days prior to first dose of study drug(s). In addition, for subjects that had brain metastases but currently have no evidence of disease (NED), NED for >=12 weeks is required and must be confirmed by two consecutive MRI or CT scans (using contrast) separated by >=6 weeks, prior to randomization. Enrollment of a subject with brain metastases who meet the above criteria requires approval of a GlaxoSmithKline (GSK) Medical Monitor.
• Psychological, familial, sociological or geographical conditions that do not permit compliance with the protocol.
• History or evidence of cardiovascular risk including any of the following: LVEF 30 days prior to randomization are eligible. History of acute coronary syndromes (including myocardial infarction a