In order to understand complex mechanisms of the tumor biology, multimodal imaging approaches are useful. Here we present a workflow to characterize subcutaneous MAT-B-III tumors in rats on a clinical 3T PET/MR. Proton imaging was used for tumor localization and to characterize tumor cellularity by diffusion-weighted imaging. Glucose uptake and downstream glucose metabolism of pyruvate by lactate dehydrogenase (LDH) was addressed by [18F]FDG-PET and hyperpolarized [13C]pyruvate metabolic imaging. The [18F]FDG standard uptake values and the LDH activity were consistently and reproducibly higher compared to normal tissue.