A marker can determine whether or not a patient has a therapeutic response to an anti-cancer agent. A novel cancer therapy employs the marker. The marker can be N-acetylglucosamine, an amino-acid-metabolism-related substance, a nucleic-acid-metabolism-related substance, a substance in the pentose phosphate pathway, a substance in the glycolytic pathway, a substance in the TCA cycle, a polyamine-metabolism-related substance, lauric acid, 6-phosphogluconic acid, butyric acid, 4-methylpyrazole, isobutylamine, glycolic acid, NADH, NAD+, or a substance involved in the metabolism of any of these substances.
