All the cells in our body carry genetic material which determines how each cell will function. This genetic material is made up of genes which are stored on 23 pairs of chromosomes. Each pair of chromosomes is numbered, 1 to 22, with the last two chromosomes being the sex chromosomes X and Y.
In about 6 out of 10 cases of acute myeloid leukaemia [AML] doctors can recognise abnormal changes in the chromosomes of the leukaemic white blood cells.

One such change is the T fifteen seventeen, which is written t(15;17). Here a piece chromosome number 15 is swapped or “translocated”with a piece of chromosome number 17. Because of this, two very important genes that are involved in the development of white cells, PML and RAR*, are disrupted and can't work properly any more. This leads to the uncontrolled growth of the leukaemia and also prevents the cells growing into normal healthy white cells. This subtype is also called acute promyelocytic leukaemia.

Slightly more than 1 in 20 people with AML have t(15;17) change on their chromosomes.

People with t(15;17) tend to respond better to chemotherapy drugs and also to treatment with a relative of vitamin A, called ATRA. Their remission rates are higher and their survival rates are also higher. Because of this people who have the t(15;17) change on their chromosomes are a 'good risk' group. So if you have AML then having t(15;17) you have a subtype of AML which responds well to treatment (ATRA combined with chemotherapy).