Disclosed is a method for treating tumor in a mammalian subject, which comprises administering a combination of (a) an anti-tumor agent and (b) a fatty acid derivative represented by the formula (I): to the subject in need thereof. The application also discloses a method for treating damages, especially gastrointestinal damages including mucositis such as stomatitis induced by an anti-tumor agent, wherein the method comprises administering a fatty acid derivative of formula (I) to the subject who is receiving the anti-tumor agent.
