Chronic myelomonocytic leukemia (CMML)

What is chronic myelomonocytic leukemia (CMML)?

Chronic myelomonocytic leukemia (CMML) affects approximately four out of 1 million people in the United States each year with about 2,000 new cases annually. The median age at diagnosis is about 72 years. CMML is rare in children.

CMML is an uncommon blood cancer that has overlapping features of two other types of blood cancers: myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPNs). The World Health Organization (WHO) has classified chronic myelomonocytic leukemia (CMML) as “myelodysplastic/myeloproliferative neoplasms.”

Major scientific advances in the past decade have allowed scientists to get a better understanding of the cytogenetic and molecular abnormalities that cause this disease. This is expected to lead to new and improved therapeutic treatments. 

You should be treated by a hematologist-oncologist, a specialist who treats people with CMML or other types of blood cancer. 

Learn how to choose a blood cancer specialist or treatment center.

What should I do if I am diagnosed with CMML?

• Talk with your doctor about your diagnostic tests and what the results mean.
• Seek treatment in a cancer center where doctors are experienced in treating patients with leukemia.
• Ask your doctor whether a clinical trial might be a good treatment option for you. 

 Learn more about communicating with your blood cancer specialist or find a list of suggested questions to ask your healthcare providers. 

How does CMML develop?

CMML starts when a stem cell in the bone marrow mutates. This results in abnormal blood cell production and an overproduction of “blasts” and immature “monocytes,” types of white blood cells that crowd out other blood cells. The blasts never mature completely into normal monocytes, so they can’t carry out their normal functions.

Over time, the abnormal monocytes accumulate in the marrow and other organs and interfere with the normal production of other types of blood cells, including red blood cells (which carry oxygen to all the tissues of the body) and platelets (which form clots to help stop bleeding after an injury).

If not treated, CMML can lead to: 

• Low numbers of red blood cells that can no longer supply an adequate amount of oxygen, a condition called “anemia”
• The immune system's inability to guard against infection effectively because of a lack of “neutrophils” (a type of white cell), a condition called “leukopenia”
• Low numbers of platelets, which can cause bleeding and easy bruising with no apparent cause, a condition called “thrombocytopenia” 

What are risk factors for CMML?

Doctors don't know why some cells become CMML cells and others don't. They've found few risk factors associated with the disease. You can't catch CMML from someone else.