People with CMML have abnormal monocytes in their blood. These cells that haven’t developed properly are also called leukaemia cells or blast cells. Too many of them means there isn't the right balance of blood cells you need to keep you healthy.

CMML is similar in some ways to the blood conditions myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPN). However, CMML is considered to be a separate condition with different treatment options because people with CMML can have problems with their blood cells that are similar to both MDS and MPN.

For between 15 and 30% of people CMML changes into another type of leukaemia called acute myeloid leukaemia (AML). This can happen after a few months or after several years.

CMML is grouped (classified) in two different ways: you'll have either CMML-1 or CMML-2, and either dysplastic CMML or proliferative CMML.

What causes CMML?

It's not clear exactly what causes CMML but we do know it mostly affects older people and people who've already had some types of cancer treatment. It's more common in men than women.  Around half of people with CMML have a change in a gene known as TET2.

CMML treatment

If you have no or few symptoms you may not need treatment straight away. Instead, you'll have regular check-ups including blood tests.

If you do need treatment, you may have non-intensive chemotherapy. Some people need more intensive treatment such as a stem cell transplant.

> You can find more information in our fact sheet on chronic myelomonocytic leukaemia (CMML)

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