Selective metabolite enrichment in TIF compared with serum. (A–C) Heatmaps show metabolites involved in TIF and serum derived from engrafted melanoma-bearing mice (A), inducible Braf/Pten melanoma mice (B), and human liver cancer patients (C). (D) Glutamine concentrations in the TME were quantitated by LC-MS in serum and TIF from human liver cancer patients (n = 7). Data in D are shown as mean ± SEM and were analyzed by two-tailed, paired Student’s t test. **P < 0.01.