This is a study to investigate the potential clinical benefit of refametinib when given in combination with sorafenib as first line treatment in patients with unresectable or metastatic HCC carrying a RAS mutation. The study will be conducted in 2 stages. Approximately 95 patients (15 at Stage 1/ 80 at Stage 2) will be accrued to this study to receive treatment. Stage 2 of the trial will only be conducted if at least 5 out of 15 patients at Stage 1 show at least partial response according to an objective criteria to evaluate tumor size based on contrast enhancement [modified response evaluation criteria in solid tumors (mRECIST)] assessed by external independent radiologists.