To provide a marker for determining sensitivity to an anti-cancer agent, which can determine whether or not a patient has a therapeutic response to the anti-cancer agent, and novel cancer therapeutic means employing the marker. The marker for determining sensitivity to an anti-cancer agent is formed of one or more substances selected from the group consisting of N-acetylglucosamine, an aminoacid-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 + , and a substance involved in the metabolism of any of these substances.
