The importance of prospective conduct

There are several widely used designs for phase II studies and we review them briefly here. Whatever the design though, a key, but sometimes neglected, feature of a phase II trial is the importance of prospective conduct. Any phase II study should aim to register its target number of patients prospectively, as this is the only means by which one can be sure that the results of the study apply to a defined cohort of patients who all began the treatment with the intention of being evaluated. It is often the case that a number of patients will have received the treatment under investigation outside of a formal trial setting, before the trial starts, and there may be understandable enthusiasm for such patients to contribute data in some way, particularly when the disease is rare. However, allowing patients to be registered retrospectively has serious drawbacks. Without systematic records and careful monitoring, it is difficult to determine whether those patients who are registered retrospectively comprise all relevant patients from that centre, or perhaps a highly selected group who did particularly well, or particularly badly, on the trial therapy. The former is perhaps the most common problem, since an obvious selection criterion is to register only surviving patients who could give their consent for their data to be used. Selecting patients for inclusion in a phase II trial on the basis of their characteristics is inevitable and does not represent a bias in assessing treatment activity. Selecting patients for inclusion on the basis of their response does introduce bias, but can be avoided by registering prospectively and accounting for all registered patients in the analysis.

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