25/10/2016 08:02 BST | Updated 19/10/2017 06:12 BST

Clinical Trials For Anti-Cancer Medicines - Should I Take Part?

People have different perceptions of clinical trials, varying from 'I'm not letting anyone experiment on me' to 'I must get into a trial with this amazing new medicine'.

So who is right?

Well, neither is wrong, but neither is the whole story.

All medicines, for cancer or anything else, must be tested in clinical trials before doctors can prescribe them. These show that the medicine works, and that it is safe.

Many medicines fail in clinical trials, either they don't work, or they have bad side-effects which outweigh any benefits. So taking an unapproved medicine within a clinical trial doesn't guarantee that it will benefit you - or that it won't harm you.

Nevertheless, some exciting new anti-cancer drugs are being tested in clinical trials. The time for development and approval to prescribe for a new medicine takes many years. Once a drug is approved, there may be the extra hurdle of a NICE assessment within the UK. So a clinical trial can sometimes provide access to a medicine, which is effective and safe but currently unavailable on the NHS.

So how do you know if a clinical trial is right for you?

Well you need to read the Informed Consent Form for the trial very carefully. In particular look for the following information:

1. What is known about how effective the drug is, and about any side-effects?

There should be a summary of the beneficial effects and side-effects which has been seen in earlier studies. But what does it mean?

The people in the first clinical trials with a potential new anti-cancer medicine usually have advanced cancer, for which there are no other effective treatments. In later studies, when more information is known, people with less advanced cancer can be included.

In some of the early studies even a modest improvement in survival (say a couple of months) may indicate a powerful drug, simply because the patients were so poorly to start with. However this doesn't mean that this is all that can ever be expected. Less sick people may improve for much longer with the same drug.

On the flip-side, in later, larger studies, where people with all degrees of cancer may be included, improvements after taking the drug may be expressed in relation to the original risk of dying, or whatever endpoint is used. This can make a medicine look misleadingly good - see my Huffington Post article on understanding medical statistics.

The bottom line is you need your doctor to explain what the study results really mean for you.

2. Will I even receive the drug?

Most clinical trials compare the drug to another treatment- either a dummy drug (placebo) or an alternative treatment, which is already approved for treating people. This is called a double-blind study. This design gives the most reliable results, as it confirms that any benefit is genuinely due to the new drug. However it means some people won't receive the new treatment.

Which trial participants receive the drug is assigned randomly by a computer and neither you nor your doctor will know whether you are receiving the real drug. Sometimes you will have a 1:2 (50%) chance of receiving the new medicine, sometimes it may be better eg 2:3.

Some studies include options for receiving the real drug later, even if you don't get it at first. For example some studies have a rescue period, where, if someone is deteriorating they can be switched to the real drug. Sometimes there is an 'open-label period' at the end of the study, where everyone can switch to the real drug.

In some studies, called 'open studies', everybody receives the real medicine from the beginning.

You must check what your chances are of receiving the medicine, at first, or at all, and what treatment you will receive if you don't have the drug.

3. What benefit can you expect?

Clinical trials are performed in a careful, step-wise fashion, to elicit the most accurate and complete information, whilst minimising unnecessary risk to patients taking part.

In the early studies, simple change in tumour size may be measured. Tumour shrinkage is useful to show the medicine has a beneficial effect. These studies are often relatively short, mainly aimed at finding how much drug can safely be given before they make someone ill. They may help you temporarily but they are not designed to make you better for a significant period of time. If you are very sick and there are few alternatives, this may still be worthwhile, but you need to know the limitations of this type of study.

Anti-cancer medicines are usually required to show that they can extend people's lives, and this is assessed in the later studies, once a safe and effective dose has been established.

In these later studies, measures such as overall survival are used. These studies are often longer studies, where drug is given for six months, a year or even longer.

Sometimes it isn't practical to measure overall survival, for instance, if people are anticipated to survive for many years, or, if they may need additional anti-cancer treatments, which could confuse the trial results, so progression-free survival is an alternative measure. This assesses survival, together with any indications that the cancer is progressing, and often provides the best information to help decide whether a cancer medicine is truly useful.

So, make sure your doctor explains exactly what the object of the study is, what they are hoping to show, and what are your options for receiving the new drug.

Taking part in a clinical trial for a new drug can be beneficial. However the drug is still under test and benefit is not guaranteed. Always read the information carefully and discuss with your doctor.

Remember, if you do take part, you can change your mind at any time, for whatever reason.

Should you be interested in clinical trials Cancer Research UK has a great tool for finding trials of benefit for you.

The EMA keeps a database on their website and there is a similar database in the USA at ClinicalTrials.Gov which also covers international studies.

Note: This expresses personal views. No warranty is made as to the accuracy or completeness of information given and you should always consult a doctor if you need medical advice.

For further information, please see my book, From Both Ends of the Stethoscope: Getting through breast cancer - by a doctor who knows.