By investigating the isotopomer patterns in l-glutamate generated from l-[U-13C]glutamine, Pham et al. deduced that the D425MED orthotopic human Myc-amplified medulloblastoma tumor preferentially uses the GTωA pathway over the glutaminase 1 (GLS1) enzyme [Equation (1)] to convert l-glutamine to l-glutamate [Equation (18)] [173]. The gene discussed is GLS; the disease is neoplasm.