Cancer and oncological therapy are associated with a progressive physical deterioration, malnutrition, and enhanced inflammatory burden. Our considerable data showing the strong anabolic potential of amino acids (AA) led us to test whether AA can acutely stimulate muscle protein synthesis in cancer patients (CA) undergoing intense chemotherapy.Mixed muscle fractional synthesis rate (FSR), rates of phenylalanine appearance and disappearance (Ra and Rd), and net phenylalanine balance (NB) were measured during a primed constant infusion of l-[ring- 2 H 5 ]phenylalanine. Blood and muscle tissue samples were collected in the basal state and following ingestion of 40g of AA given in 30mL boluses every 10min for 3h. Serum and tissue cytokines and NF-κB expression in skeletal muscle were measured and compared to normative, healthy older controls (OC).Skeletal muscle TNF-α, IL-6, and NF-κB were elevated in CA. FSR and model-derived protein synthesis (Rd) increased significantly from basal to AA (FSR: 0.052±0.009 vs. 0.120±0.008%h −1 , P<0.001; Rd: 23.1±4.1 vs. 36.4±5.0nmolmin −1 100mLleg −1 , P⩽0.05). Model-derived protein breakdown (Ra) remained unchanged from basal to AA. Phenylalanine NB improved from a negative basal value (−16±2) to zero (0.8±6nmolmin −1 100mlleg −1 , P⩽0.05) following AA.Despite advanced cancer, ongoing therapy, and an enhanced inflammatory burden, AA were capable of acutely stimulating muscle protein synthesis in these patients.