Phase II studies in oncology have evolved over the previous several decades. Currently, the number of drugs in phase II development has increased, and patient eligibility has narrowed due to targeted agents, competing trials and curative therapies in the first-line setting. As a result of these changes, more attention needs to be focused toward conducting more efficient phase II trials. Given the increased difficulty in accruing patients to phase II studies and the ethical concern of treating patients with agents that are ineffective, there is significant motivation to stop a single arm trial early when the investigational agent shows evidence of a low response rate
