The early stages of testing a new treatment can be done relatively quickly, in a matter of a year or two. These trials look at the side effects and safety of the treatment and also get an idea of how effective it might be. They are often called Phase 1 and Phase 2 clinical trials.

If a treatment gets through Phase 1 and 2 trials successfully then the next stage is to compare it with the best currently available treatment. This is called a Phase 3 trial. These trials can often take a very long time to complete. There will always be a period of some months, or even years, spent in planning the trial and getting approved by Research Ethics Committees. Once this has been done the trial itself can be 'launched' and people 'recruited' as volunteers to take part.

The time from the launch of a Phase 3 trial to the publication of its final results can vary from a year or so to decades. There are a number of reasons for this but some of the more important factors are:

• the number of patients needed to complete the trial: although great progress has been made in cancer treatment in the last fifty years this has almost always been the result of a host of small improvements, rather than the discovery of 'miracle cures' or 'wonder drugs'. This means that although a new treatment might be better than the 'old' treatment the difference between them is usually quite small and will only be clear if a large number of people are given the two treatments and then compared. As a consequence most Phase III trials today will involve at least hundreds, and usually thousands, of people in order to get an accurate result. So finding sufficient people who are both suitable for any one trial and also willing to take part in that trial, can take a long time.
• the rarity of the cancer being treated: some cancers are much commoner than others. So a Phase III trial in breast cancer, lung cancer or bowel cancer (all of which are very common) is likely to recruit the number of patients it needs far more quickly than, say, a trial for testicular cancer or melanoma (which are relatively uncommon).
• what the trial is measuring: different Phase 3 trials measure different things and this affects the time they take to get a result. For example, if a trial is measuring the survival of people who have very advanced cancer, with a life-expectancy of only a few months, then any improvement would become apparent quite quickly. On the other hand if a trial is looking at treatment given after surgery for early cancer, where the hope might be to raise cure rates from, say, 70% to 80% then patients might have to be followed up for 5 or even 10 years, to make sure they have been cured, and to find out whether the treatment has helped.

Although it would be ideal if the results could be discovered earlier it is vitally important that Phase 3 trials are done properly so that the best possible treatment can be worked out. Unfortunately this often takes a long time, but there is almost universal agreement among doctors and scientists that Phase 3 clinical trials are the best way of deciding if a new treatment really does have anything to offer.