Introduction to Clinical Trials
What is a Clinical Trial?
Any planned experiment which involves patients and is designed to reveal the most appropriate treatment of future patients with a given medical condition. It uses results based on a limited sample of patients to make inferences about how treatment should be conducted in the general population of patients who will require treatment in the future.
The majority of clinical trials are concerned with the evaluation of drug therapy, but they can also be concerned with other forms of treatment, eg surgical procedures, radiotherapy, etc., or quality of life, etc.
Clinical trials fall into 4 phases:
Phase I - to determine an acceptable drug dosage
Phase II - to provide evidence of efficacy of treatment
Phase III - to compare efficacy/side effects with those of other drugs/treatments/placebo
Phase IV - large scale epidemiological study (mainly industry)
Phase I Trials
Phase I trials can be seen as toxicity screening studies where, after testing in the laboratory and on animals, a new drug is administered for the first time in man in order to determine the maximum tolerated dose. (Of the many new drugs manufactured, only a very small number actually get to this stage). There are usually two aims of a phase I trial - to establish optimal dose to be used in a phase II trial for drug efficacy, and to determine the type and degree of toxicity (adverse effects) associated with the drug. Dose limiting toxicity (DLT) is the point at which an unacceptable level of toxicity is identified. The dose level below that at which DLT is identified in 2 of a maximum of 6 patients is known as the maximum tolerated dose (MTD), ie the optimal dose to be taken forward to a phase II study. Because of their complexity, phase I trials only take place in UKCCSG centres which fulfil the specific requirements for Phase I studies. Patients entering Phase I trials will have failed on conventional therapy.
Phase II Trials
After determining the recommended dose in a limited number of patients in Phase I trials, new drugs are subjected in Phase II trials to their initial screen in man for possible anti-tumour activity. The goal of a Phase II trial is thus to identify in a small number of patients those drugs of potential promise for more intensive testing in a given population or tumour type. The endpoints of such a trial are response rate and toxicity.
Phase III Trials
After a drug is found to have at least some minimal amount of anti-tumour activity in Phase II trials, the next step is to determine its relative efficacy in a larger Phase III trial. Here the drug will be compared, either alone, or in combination with other drugs, to a control group, usually the best available treatment, or a historical control.
Most CCLG trials are Phase III, comparing patients on a new treatment versus standard treatment, to try and establish whether treatment A is better than treatment B.
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