Chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) is very rare in children.

Most childhood leukaemias are ‘acute’ meaning that they develop and progress rapidly. CML is a chronic leukaemia, meaning it develops slowly, often over many years.

About chronic myeloid leukaemia

Leukaemia is a cancer of the white blood cells.

White blood cells help to fight infection. There are two different types: lymphoid cells (lymphocytes) and myeloid cells. CML affects the myeloid cells.

Normally the white blood cells, which are produced in the bone marrow, repair and reproduce themselves in an orderly and controlled way. In leukaemia, however, the process gets out of control and the cells continue to divide but do not mature.

These immature dividing cells – known as blast cells - fill up the bone marrow and stop it making healthy blood cells. As the blast cells are immature, they cannot work properly. This puts the child at increased risk of infection. The overproduction of white blood cells also interferes with the production of healthy red blood cells and platelets, leading to symptoms such as anaemia and bruising.

In contrast to the acute leukaemias, this happens very slowly in CML.

There are three different stages in the development of CML:

Chronic phase. There may be no symptoms of leukaemia, but blast cells are present in the blood and bone marrow. This phase can last several years before undergoing transformation to the second, accelerated phase.
Accelerated phase. An increased number of blast cells are found in the blood and marrow and there is evidence that the number of normal cells is decreasing. This phase lasts three to nine months.
Blast phase. Also called a ‘blast crisis’. During the third and final phase, the disease resembles acute leukaemia. More than 30 per cent of bone marrow and blood cells are blast cells. Without effective treatment (see below) the disease is usually fatal within three to six months of entering the blast phase.

Incidence

CML is rare in children. Less than 15 new cases of childhood CML are diagnosed annually in the UK. These are most likely to be in the older age groups.

Read more: Incidence of childhood leukaemia

Survival

Until the 1960s childhood leukaemia was incurable. Today, children diagnosed with CML have around a 60 per cent chance of survival.

Diagnosis

With CML, there are usually no symptoms in the early stages. Often, CML may be discovered when the child is having a routine blood test for other reasons.

When symptoms do occur, they are quite general, including

frequent, persistent infections
unusual bleeding and bruising
tiredness
paleness and
breathlessness

There may also be bone/joint pain, abdominal pain and/or swollen lymph nodes.

Children may have some or all of these symptoms.

Treatment

When a diagnosis of leukaemia is confirmed, the child will be referred immediately to one of the UK’s 21 specialist paediatric oncology centres for treatment.

Further tests will be carried out to provide doctors with as much information as possible about the child’s disease.

Unlike the acute leukaemias, childhood CML cannot be cured by any type of chemotherapy although a new drug called Imatinib can eliminate easily detectable signs of leukaemia from the blood, prolonging the chronic phase of the disease and delaying transformation to the accelerated stage.

The only treatment that can cure childhood CML is a stem cell transplant.

Read more: Treating chronic myeloid leukaemia