It is very important to participate into international clinical trials for cancer treatment not only for contribution to worldwide development of new anticancer agents but also for escape from social isolation out of new drug development. Here, we discussed about international clinical trials in Japan as an aspect of medical oncologist in medical school. And also, according to only one our experience of international clinical trial, IDEAL 1, which was a randomized phase II study of gefitinib for patients with previously treated metastatic non-small cell lung cancer, I tried to consider about current challenges of study investigators for cancer treatment, study conducting institution, pharmaceutical company, and regulatory agent in Japan.