[Introduction to the statistical aspects of planning clinical oncologic phase III studies].

A phase III clinical trial is a comparative study in which one assesses the relative efficacy of a treatment or treatments. It generally has one of the following objectives: 1. To determine the effectiveness of a new treatment relative to the natural history of the disease, for example when comparing a new treatment to not treatment or to placebo in an adjuvant setting. 2. To determine if a new treatment is more effective than the best current standard therapy (at the risk of increasing the toxicity). 3. To determine if a new treatment is as effective as the best current standard therapy but is associated with less severe toxicity or a better quality of life (equivalence trial). Clinical trials must be properly designed in order to answer such questions with a high degree of certainty. The purpose of this paper is to present several concepts which must be taken into account during the process of designing a clinical trial.