A new adaptive design based on Simon's two-stage optimal design for phase II clinical trials

Phase II clinical trials are conducted to determine whether a new agent or drug regimen has sufficient promise in treating cancer to merit further testing in larger groups of patients. Both ethical and practical considerations often require early termination of phase II trials if early results clearly indicate that the new regimen is not active or worthy of further investigation. Simon's two-stage designs (1989) are common methods for conducting phase II studies investigating new cancer therapies. Banerjee and Tsiatis (2006) proposed an adaptive two-stage design which allows the sample size at the second stage to depend on the results at the first stage. Their design is more flexible than Simon's, but it is somewhat counter-intuitive: as the response in the first stage increases, the second-stage sample size increases till a certain point and then abruptly becomes zero. In this paper, based on Simon's two-stage optimal design, we propose a new adaptive one which depends on the first stage results using the restrict conditions the conditional type I error and the conditional power. Comparisons are made between Banerjee and Tsiatis' results and our new adaptive designs.