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Phase 1

Phase 1 trials of new cancer treatments use drugs which have been tested on cancer cells in the laboratory and have had an effect. Phase 1 is the first stage in which the drugs are used to treat patients. These studies have small numbers of patients. Phase 1 drugs are offered to people whose cancer has come back or spread, and there is no other standard treatment that may help them. It is not expected that the treatment will cure the cancer; rather, the trial aims to find out:

  • How much of the treatment can be given without causing serious side effects.

  • Which side effects the drug causes.

  • Whether the drug has any effect on the cancer.

In a phase 1 trial the first group of between 3 to 6 patients are given a small dose that is expected to be safe. If none of the patients have any side effects the next group of patients will be given a higher dose. In this way the dose of the drug is increased until some people do have side effects. When side effects are seen that make it unsafe to increase the dose further it is known as the Maximum Tolerated Dose and the dose is not increased any more.

it is impossible to predict whether a new treatment will cause harmful side effects in people, and it is important that patients in this type of trial are monitored carefully. Phase 1 trials are usually carried out in clinical research units at specialist hospitals, rather than in local hospitals, and this may involve a lot of travelling to and from the center.

If the drug has an effect on the cancer, and a safe dose has been found, the drug will then be tested in phase 2 trials.

Phase 2

By the time a treatment reaches phase 2, researchers will know quite a lot about it. The phase 1 trials will have shown what the major side effects are and whether the drug actually has some effect on particular types of cancer. The aim of phase 2 trials is to look at how many people the treatment is effective for and which types of cancer it might be used to treat. Researchers will know which side effects may occur so they can deal with these straight away if necessary.

Phase 2 studies have more patients, perhaps a few dozen. These patients will be closely monitored to see whether their cancer is getting smaller. If the cancer does shrink this is known as a response to treatment. The trial will also look at any side effects caused by the treatment. Sometimes phase 2 studies include different ways of giving the new treatment; for example, patients may be given the same drug by injection, or as tablets. These trials may be randomized.

Phase 3

These studies follow phase 2 and the main aim is to compare the effectiveness and safety of the treatment being tested with current treatments. Hopefully, one will be found to be more effective, although it may be just as useful to find that they are all equally effective but one has fewer side effects. Phase 3 trials are large and usually include hundreds, or sometimes thousands, of patients from many different hospitals, often from several countries. Researchers measure various aspects, such as whether the growth of the cancer slows, and, in the longer term, how long patients remain free of cancer. Researchers may also measure how the treatment affects patients' quality of life. Phase 3 trials always involve randomization.

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