Providing a novel cancer treatment method that exhibits markedly superior antitumor effects and has few side effects. An antitumor agent, wherein a DNA dysfunction agent and an immunomodulator are administered in combination.顕著に優れた抗腫瘍効果を示し、副作用の少ない新規な癌治療方法の提供。 DNA機能障害剤と免疫調節剤を併用投与することを特徴とする抗腫瘍剤。