Chronic myelomonocytic leukemia is a rare cancer with features that overlap both myelodysplastic syndromes and myeloproliferative neoplasms.  

But what distinguishes this particular type of leukemia from others? How do its symptoms differ? And, is it curable? Read on for the answers to these questions and more. 

What makes chronic myelomonocytic leukemia unique? 

Chronic myelomonocytic leukemia is not a single entity. It’s more like a group of diseases. That’s why it shares features with both myelodysplastic syndrome and myeloproliferative neoplasms. All of these are chronic bone marrow disorders that affect stem cells.  

Here’s how I usually explain them to my patients: 

Myelodysplastic syndrome (MDS)

Genetic errors prevent stem cells from maturing properly, so they look abnormal under a microscope and patients tend to have low white blood cell counts, hemoglobin values or platelet counts. 

Myeloproliferative neoplasms (MPN)

Genetic errors cause bone marrow to overproduce different types of blood cells, such as red blood cells in polycythemia vera or platelets in essential thrombocythemia. In other cases, myelofibrosis, which is scarring of the bone marrow, can develop. 

Chronic myelomonocytic leukemia (CMML)

Genetic errors in stem cells can simultaneously reduce the bone marrow’s ability to produce normal levels of red blood cells or platelets, causing low blood counts, and over-produce white blood cells. In CMML, there is a significant increase in a unique type of white blood cell called monocytes. Because of these overlapping aspects, in cases where CMML shows more of the low counts without white blood cell increase, the disease is called myelodysplastic. On the other hand, if CMML causes an elevation in white blood cells, it is called myeloproliferative. 

Keep in mind that chronic myelomonocytic leukemia is very rare. It is most common among the elderly, and typically occurs between ages 68 and 70. About 60% of those diagnoses occur in men. 

What are the earliest signs of chronic myelomonocytic leukemia? 

Chronic myelomonocytic leukemia is usually found through abnormalities in routine bloodwork. Someone might discover they have anemia during an annual physical, for instance, or their monocyte count may be consistently elevated, and that will lead to a diagnosis.  

Chronic myelomonocytic leukemia is also associated with various rheumatologic disorders, including rheumatoid arthritis and lupus. These can mimic the symptoms of CMML. So, sometimes, it is found that way, when someone seeks treatment for one of those diseases. 

How do the symptoms of chronic myelomonocytic leukemia differ from others?

Because CMML is not a single entity and occurs on a spectrum, how the disease looks in a particular individual depends entirely on what type of CMML a patient has. And that is determined by the type of mutations that led to the disease emerging.  

Patients whose blood counts are low, for instance, might show no symptoms at all for several years, or only those associated with low blood counts, such as fatigue, anemia or bruising easily. Patients with more proliferative features, on the other hand, might have an enlarged spleen and show more “B symptoms,” such as night sweats, weight loss, fevers, or skin rashes.  

Symptoms can vary greatly, depending on the person. That’s why it’s so important to see a specialist at a place like MD Anderson, which does research on this disease.  

CMML is very rare. But how it’s managed can differ quite dramatically, depending on your symptoms and whether the disease is considered high-risk or low-risk. Some patients only need observation, while others need an immediate allogeneic stem cell transplant or a clinical trial using new drugs or drug combinations. The possibilities are very broad. 

What are the final stages of chronic myelomonocytic leukemia? 

With time, chronic myelomonocytic leukemia can potentially evolve in one of three ways.  

• Bone marrow failure: This requires repeated blood transfusions and makes infections more likely. People with bone marrow failure usually die from complications of chronically low blood counts. 
• Transformation into acute myeloid leukemia: Once this happens, the disease becomes more aggressive, and an allogeneic stem cell transplant should always be considered. 
• Unrelated complications: These are considered a result of the disease, but not necessarily a feature of the disease. Examples include heart or kidney failure. 

Unfortunately, there are no approved and effective standard treatments for any of these scenarios. That’s why seeking care in centers where clinical trials are available becomes critical. Research directed at understanding how CMML occurs and progresses continues to expand rapidly, thanks to academic centers like MD Anderson. This is helping us develop novel clinical trials. 

What’s the average life expectancy for someone with chronic myelomonocytic leukemia?

That depends on the person. Everyone is different. It can range from a median of 1.5 years after diagnosis up to about 8 years. More aggressive variations of the disease will require more involved and prompt treatments. With slower-moving variations, often we can just monitor patients and treat their symptoms. 

Is chronic myelomonocytic leukemia curable? 

The only potentially curative treatment for chronic myelomonocytic leukemia right now is an allogeneic stem cell transplant. Although its success rate is not 100%, it is currently the best option we have and can lead to good results. 

That’s why we’re exploring different treatments through clinical trials. We have several underway right now that target this disease specifically. One involves a new drug called STX-0712 that uses the immune system to kill CMML cells. Others combine decitabine or azacitidine with new drugs that affect the ways leukemia cells mature, such as seclidemstat or EP36170. Other treatments rely on new chemotherapies to kill the leukemia cells.  

Because CMML is so rare and the way it behaves can vary so greatly, we are trying to approach the disease from many different angles. That’s why every patient with CMML would benefit from seeing a specialist at a facility that does research, like MD Anderson. Treatment options are already so limited for CMML that expertise is required to fully understand your disease and give you the best possible outcome. 

Guillermo Montalban Bravo, M.D., is a leukemia specialist with a particular interest in chronic myelomonocytic leukemia.  

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