Phase III clinical trials are often expanded randomized studies in larger patient populations. These studies are designed to obtain further information about the effectiveness of the agent and safety. In these trials, the endpoint is a difference in disease free survival and overall survival as compared with the conventional treatment. Of all current gene therapy trials only 2.6% are clinical phase II/III or III trials (3). Validation of gene therapy strategies will require more phase III trials to be performed yet the large number of potential gene therapeutics and the limited number of patients makes careful design of phase III studies critical. Additionally, the problem of limited numbers of patients may be reduced by properly designed phase II studies that utilize correlative studies to identify sensitive subsets so that large cohorts of patients do not have to be evaluated in phase III randomized setting to achieve statistical significance.
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