Part 2: Comparison of the safety and efficacy of rilotumumab or ganitumab in combination with panitumumab versus that of panitumumab alone. In Part 2, participants were randomized 1:1:1 into 3 cohorts: 6 mg/kg panitumumab plus 10 mg/kg rilotumumab, 6 mg/kg panitumumab plus 12 mg/kg ganitumab, or 6 mg/kg panitumumab and placebo (panitumumab alone cohort). Panitumumab was administered open-label, and rilotumumab and ganitumab were double-blinded.