Patent ID: 7470714

Claim:
A method for enhancing an antitumor effect of an antitumor substance on cancer cells comprising administrating a compound of the following formula (1) or a pharmaceutically acceptable salt thereof in combination with the antitumor substance to the cancer cells, wherein said antitumor substance is different from said compound of the following formula (1) or a pharmaceutically acceptable salt thereof: wherein each R represents a hydrogen atom, and wherein said antitumor substance is selected from the group consisting of a pyrimidine compound, an anthracycline compound, a vinca alkaloid, a topoisomerase type II inhibitor, and Cisplatin, and wherein said cancer is selected from the group consisting of stomach cancer, colon cancer, pancreatic cancer, ovarian cancer, prostatic cancer, osteosarcoma and/or soft part sarcoma, skin cancer, and leukemia.