http://www.cancerhelp.org.uk/help/default.asp?page=73
There are 4 different types of clinical trials. These are called phase 1,
2, 3 and 4.

Phase 1 (phase I)

These are the earliest trials in the life of a new drug or treatment. They
are usually small trials, recruiting anything up to 30 patients (often a
lot less). The trial may be open to people with any type of cancer.

When laboratory testing shows a new treatment might help treat cancer,
phase 1 trials are done to find out

   * The safe dose range
   * The side effects
   * How the body copes with the drug
   * If the treatment shrinks cancer

The first patient to take part will be given a very small dose of the
drug. If all goes well, the next person will get a slightly higher dose.
With each patient taking part, the dose will gradually be increased and
the effect that has will be monitored. Any side effects will be recorded.
In a phase 1 trial, you may have lots of blood tests, as the researchers
look at how the drug is affecting you. And at how your body copes with,
and gets rid of the drug.

People entering phase 1 trials often have advanced cancer and have usually
had all the treatment available to them.  This is because they may benefit
from the new treatment in the trial, but many won't.  The aim of the trial
is to look at doses and side effects.  This work has to be done first,
before we can test the potential new treatment to see if it works.  Phase
1 trials are important because they are the first step in finding new
treatments for the future.

Phase 2 trials (phase II)

About 70 out of every 100 new treatments tested at phase 1 make it to
phase 2 trials. These trials may be done on people who all have same type
of cancer, or with several different types of cancer. Phase 2 trials are
done to find out

   * If the new treatment works well enough to test in phase 3
   * Which types of cancer it is effective against
   * More about side effects and how to manage them
   * More about the most effective dose to use

Although these treatments have been tested at phase 1, you may still have
side effects that are not known about. Drugs can affect people in
different ways.

Phase 2 trials are often larger than phase 1. There may be up to 50 people
taking part. If the results of phase 2 trials show that a new treatment
may be as good as existing treatment, or better, it then moves to phase 3.

Phase 3 (phase III)

These trials compare new treatments with the best currently available
treatment (the standard treatment). They may compare

   * A completely new treatment with the standard treatment
   * Different doses or ways of giving a standard treatment
   * A new radiotherapy schedule with the standard one

Phase 3 trials are usually much larger than phase 1 or 2. This is because
differences in success rates may be small. So, you would need very many
results to show the difference.

For example, 6% more people get a remission with a new treatment compared
to standard treatment. If a phase 3 trial gave the new treatment to 50
people and the standard treatment to 50, on average, there may be 3 more
remissions in the new treatment group. The 2 groups would not look that
different. If they gave each treatment to 5,000 people, there could be 300
more remissions in the new treatment group.

Sometimes phase 3 trials involve thousands of patients in many different
hospitals and even different countries.

Randomisation

Phase 3 trials are usually randomised. This means the researchers put the
people taking part into 2 groups at random. One group gets the new
treatment and the other the standard treatment.  There is more about
randomisation and types of trials on the next page in this section.

Overviews

Trial overviews are studies that combine all the results from phase 3
trials of a new treatment. They are sometimes called meta-analyses. The
idea is to get a broader picture of how well a treatment works. The more
data (information) you have, the more accurate the results are likely to
be.

Phase 4 (phase IV)
Phase 4 trials are done after a drug has been shown to work and has been
granted a license.  So they are looking at drugs that are already
available for doctors to prescribe, rather than new drugs that are still
being developed.

The main reasons pharmaceutical companies run phase 4 trials are to find
out

   * More about the side effects and safety of the drug
   * What the long term risks and benefits are
   * How well the drug works when it’s used more widely than in clinical
trials

There is more information about the different phases of clinical trials on
the website of The Association of the British Pharmaceutical Industry
(ABPI). http://www.abpi.org.uk//publications/briefings/clinical_brief.pdf
(Adobe Acrobat file)