In this chapter, we provide an overview of the general process by which a new treatment is evaluated; from initial clinical investigation through to widescale clinical practice. We review the factors which may determine, at each stage, whether or not a new clinical trial is warranted. Crucial to this is knowing what you want to have achieved by the time each stage is completed.

Ideas for new therapies and for new trials may emerge from many sources, but all will have in common the hope that they will - in some way - lead to a better therapy for a given condition. They may be anticipated to improve survival, to provide a better toxicity profile, to be more convenient or more widely applicable than standard therapy or perhaps to offer a combination of these factors. To establish whether or not the new therapy really does bring these benefits will ultimately require a direct comparison with the current best standard treatment in a large group of patients, not least because there may be a fine balance between gains and losses with a new therapy. However, a large multi-centre trial is a major undertaking which should only be embarked upon if the case for doing so is strong. The questions addressed must be clinically important, scientifically informative and ethically sound, and must be accorded high priority by the clinical and patient communities involved. A 'screening process' is therefore necessary to ensure a high chance that therapies which are ineffective, impractical or inappropriate for whatever reason are rejected at an early stage. Typically therefore, new therapies go through many stages of testing, both pre-clinical and clinical. We begin by describing a widely used categorization of clinical trials which mirrors the typical process of development of therapies from the first clinical developments to widescale use in clinical practice.

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