Positron emission tomography (PET) with [2-18 F]-2-fluoro-2-deoxy-D-glucose ([18 F]FDG-PET) was acquired at multiple time-points a) to monitor the early response to RO5126766 (CH5126766) in xenograft models b) to evaluate non-invasive small animal [18 F]FDG-PET imaging as a biomarker for MEK inhibitors for translation into dose-finding studies in cancer patients and c) to explore the underlying mechanism related to FDG uptake in tumors treated with RO5126766. This evidence concerns the gene MAP2K7 and cancer.