CMML (chronic myelomonocytic leukaemia): symptoms, diagnosis and treatment

Blood cells are made in the bone marrow, the soft inner part of the bones. All start from stem cells, which make immature cells that develop into red cells to carry oxygen, white cells to fight infection and platelets to help the blood clot. In CMML a specific type of white cell, the monocyte, is increased and abnormal. Cancer Research UK explains that too many are produced and they are not developed enough to work properly, and that it becomes harder for the marrow to make good-quality red cells, platelets and other white cells.

CMML is classed as an overlap disorder. It has features of both myeloproliferative neoplasms, in which too many blood cells are made, and myelodysplastic syndromes, in which the cells are abnormal and not fully mature. Blood Cancer UK describes two broad patterns: MD-CMML, where low blood counts predominate, and MP-CMML, where high white cell counts and their effects dominate.

CMML usually develops slowly and may not cause symptoms at first. Symptoms, when they come, are mostly due to the effects of low normal blood counts or an enlarged spleen.

• Tiredness, pallor and sometimes breathlessness from a low red blood cell count (anaemia).

• Infections that do not get better or that last longer than normal.

• Nosebleeds or easy bruising from a low platelet count.

• Tummy discomfort or feeling full after small meals from a swollen spleen, felt on the upper left side.

• Weight loss, loss of appetite, sweating and night sweats.

• Skin rashes, lumps or itching.

• Aches and pains in the bones, muscles or joints.

Cancer Research UK says the cause of most cases of CMML is not known. The risk increases with age. Sometimes CMML is caused by radiotherapy or chemotherapy given for another cancer, which is called therapy-related CMML.

Research has found gene changes that are important in CMML, including changes in genes such as TET2, SRSF2, ASXL1 and RUNX1, and many people have more than one. These are acquired changes in blood cells rather than inherited conditions in the family, and testing them helps doctors plan treatment.

Blood Cancer UK advises making an appointment with your GP if you notice symptoms, noting that they are usually explained by something else that is not cancer. Doctors look for a consistently high level of monocytes in the blood and bone marrow, fewer than 20% blast cells in the blood and bone marrow, no sign of other related conditions on a blood smear and certain genetic changes.

The tests include a full blood count, a blood smear examined under a microscope, and often a bone marrow biopsy taken from the hip bone under local anaesthetic. Blood Cancer UK says it normally takes 1 to 2 weeks to get the results of a bone marrow biopsy. Cancer Research UK adds that cytogenetic tests look for chromosome changes and next-generation sequencing for gene changes.

The World Health Organisation divides CMML into CMML-1, with fewer than 5% blasts in the blood and fewer than 10% in the bone marrow, and CMML-2, with 5 to 19% blasts in the blood and 10 to 19% in the marrow. This helps the team decide on outlook and treatment.

Treatment depends on the type of CMML, whether you have symptoms, your age and other medical conditions. Cancer Research UK explains that people with few or no symptoms may be monitored with regular check-ups and blood tests, sometimes called watchful waiting or active monitoring, and that treatment usually starts if symptoms get worse or the disease progresses.

Cancer Research UK says transformation to AML might happen after a few months or after several years, and that CMML-2 has a higher risk of transformation. Because the course varies so much, your haematology team will explain the likely outlook based on your type, blood counts, gene changes and general health.

Cancer Research UK points out that coping with a rare condition can be difficult both practically and emotionally. Clinical nurse specialists, charities such as Blood Cancer UK and Leukaemia Care and support groups can help. Contact your team promptly if you develop a fever or any sign of infection, because infection is an important risk when blood counts are low.

On the NHS, CMML is diagnosed and treated by haematology teams, usually at a hospital that has access to bone marrow testing and genetic analysis, and discussed in a multidisciplinary meeting. Treatment on the NHS is free at the point of use, and your clinical nurse specialist is your main contact.

Some people seek a private haematology opinion to obtain a second view on the diagnosis or on whether transplant is suitable. The underlying tests and drugs are the same, and choices about transplant are made with a specialist transplant centre.