The invention surprisingly found that antcin or an ester derivative, salt or a composition thereof in combination with an anti-tumor drug provides unexpected efficacy in inhibiting tumors, while retaining normal cells at high viability. In addition, the amount of the anti-tumor drug in chemotherapy can be reduced by combinatorially using antcin or an ester derivative, salt or a composition thereof in view of the fact that they play a role in adjuvant therapy.
