If you take thousands of people with acute myeloid leukaemia (AML) and treat them all the same, with the same combination of chemotherapy and the same supportive care, using antibiotics and blood and platelet transfusions, about half will be alive and free of leukaemia 5 years later. We know this from the results of many big clinical trials looking at the outcome of chemotherapy for people with AML.

This figure of half is a great improvement from only 50 years ago, when AML was always an incurable disease. But, understandably, most patients want to know what their individual chances are, not those of large groups of very different patients who have gone into trials. To try and answer this, cancer doctors have tried to pick out things, known as risk factors, that will predict how someone will respond to treatment and how likely they are to be cured. These 'risk factors' can be either good,  intermediate or bad. The main ones that have been identified are:

• Age: as people get older, the chances of the bone marrow going back to normal and the leukaemia staying away get smaller. This gets more of a problem with increasing age. This is due partly to the disease being more resistant to chemotherapy in older people and also to being less fit to withstand the treatment.
• Chromosome changes: the chromosomes carry all the genetic information in our cells. There are 23 pairs in a normal cell. In AML the chromosomes can be disrupted, with pieces swapped from one to another, or pieces of whole chromosomes gained or lost. Some of these changes happen more commonly than others. It has been shown that some of these changes are associated with a good outcome and others are associated with a poorer outcome. From the results of the clinical trials it has run the Medical Research Council in the UK has found 3 chromosome changes which appear to show a 'good risk'. (These are: inversion (16) - where a piece of one chromosome 16 has been turned back to front; t(8;21) -where a piece of chromosome 8 has been swapped with a piece of chromosome 21 and t(15;17) - where a piece of chromosome 15 has been swapped with a piece of chromosome 17)
• Response to treatment: people whose bone marrow goes back to normal after the first course of chemotherapy do better than those who still have some leukaemia left.

When your doctor tells you that you have 'good risk' AML it is likely that she means that you have one of the 3 chromosome changes mentioned above. It may also mean that you are aged less than 55 and that your bone marrow became normal after your first course of treatment. These 3 factors would mean that you are likely to have a better outcome than average. In addition, people who are good risk are not usually considered for strong treatments such as bone marrow transplants as their chances of being cured just with chemotherapy are good.

It is important to understand that your doctor is basing all these estimates of risk on the results from clinical trials treating thousands of patient, over, many years, and identifying smaller groups in those thousands that seem to do better. Remember, it is still very hard to make detailed predictions about one individual patient. There will always be good risk patients who do not respond as predicted. The good risk things your doctor knows about your leukaemia are only a guide and not a guarantee of success and not having the good risk factors does not mean you will definitely not do well.