CMML vs. CML: What’s the Difference?

Both CMML and CML impact myeloid stem cells. Myeloid stem cells develop into the following types of cells:

• red blood cells (RBCs)
• white blood cells (WBCs)
• platelets

Let’s get into the key differences between CMML and CML in terms of how each can affect these cells.

CMML

CMML is characterized by high levels of WBCs called monocytes. Many of these monocytes are poorly developed and don’t function well. An increase in WBCs that aren’t fully mature — known as blasts — can also happen.

One way to categorize CMML is by using the number of blasts present in the blood and bone marrow:

• CMML-0. This category indicates less than 2 percent blasts in the blood and less than 5 percent blasts in the bone marrow.
• CMML-1. There category indicates 2 to 4 percent blasts in the blood and 5 to 9 percent blasts in the bone marrow.
• CMML-2. This category indicates more than 5 percent blasts in the blood and 10 to 19 percent blasts in the bone marrow.

CML

CML happens when myeloid stem cells divide uncontrollably, making high numbers of blasts that do not work properly. The WBCs impacted are called granulocytes.

CML has 3 phases based on the number of blasts in the blood and bone marrow as well as the severity of symptoms:

• Chronic. This phase indicates less than 10 percent of cells are blasts, and you may not have symptoms. Most people are diagnosed in this phase.
• Accelerated. This phase indicates 10 to 19 percent of cells are blasts. Symptoms often begin in this phase. New mutations may also happen, making some treatments less effective.
• Blastic. Blasts make up 20 percent or more of cells in this phase. Symptoms become much more severe and can be life threatening.

It’s possible to have CMML or CML and not to experience symptoms. In fact, you may only find out about your condition when routine blood tests show abnormal blood counts.

In general, symptoms of CMML and CML are similar and can include:

• weakness and fatigue
• night sweats
• fever
• unintentional weight loss
• feeling full shortly after eating
• shortness of breath
• bone pain
• anemia
• bruising or bleeding easily
• frequent infections
• enlarged spleen
• enlarged liver (CMML only)

See a doctor if you’re experiencing any of the symptoms above. A doctor can suggest tests that can help determine what’s causing your symptoms.

The exact causes of both CMML and CML are unknown. But we do have insight into some of the genetic factors involved in the development of these cancers.

CMML

CMML is linked to genetic changes in myeloid stem cells that cause too many monocytes to be produced. These changes don’t appear to be inherited — meaning that they likely occur during your lifetime.

Several genes have been found to be associated with CMML — including TET2, a gene that codes for a protein that helps control monocyte levels. About 50 percent of people with CMML have changes in this gene, according to Cancer Research UK.

CMML can also be caused by cancer treatments like chemotherapy or radiation therapy. Therapy-related CMML accounts for about 10 percent of CMML diagnoses, per Leukaemia Care.

CML

Around 90 to 95 percent of people with CML have a specific type of chromosome called the Philadelphia chromosome. This happens when DNA is swapped between two chromosomes during cell division.

When this occurs, a new fusion of the genes BCR and ABL1 is created. BCR-ABL1 makes an abnormal enzyme that can cause too many myeloid cells to be produced.

The Philadelphia chromosome is not inherited. It happens in the bone marrow by chance during your lifetime — the exact cause is not yet known.

Treatment options for CMML and CML differ in several ways.

CMML

If CMML is not causing symptoms, your healthcare professional may recommend a period of watchful waiting during which they’ll regularly monitor your condition. When symptoms do occur, they’ll start treatment.

A stem cell transplant (SCT) may be recommended for younger individuals with CMML who have limited or no health concerns. An SCT has the potential to cure CMML.

CMML can also be treated with chemotherapy. This treatment can kill cancer cells or slow their growth. But chemotherapy cannot cure CMML.

CML

CML treatment depends on what phase of the condition you’re in:

• Chronic. Tyrosine kinase inhibitors (TKIs) are often used successfully in this phase. Examples of TKIs include imatinib (Gleevec) and dasatinib (Sprycel).
• Accelerated. TKIs can be used, but may be less effective. Your current TKI dosage may be increased, or you may be switched to a new TKI. Chemotherapy may also be given along with a TKI.
• Blastic. TKIs are much less effective in this phase. Since blastic CML can act like acute leukemia, chemotherapy for these types of leukemia may be effective.

A stem cell transplant can potentially cure CML in younger people with limited or no health concerns. But it’s typically recommended when CML does not respond well to TKIs or if the cancer has progressed past the chronic phase.

In many cases, having regular check-ups with a doctor and sticking closely to prescribed medication regimens are the most important steps that you can take so that your treatment plan can be adjusted accordingly.

Treating CMML or CML also involves supportive care to help relieve symptoms and prevent complications that often result from low blood counts. Some examples of supportive care include:

• blood or platelet transfusions
• medications to increase the production of RBCs
• antimicrobial medications to prevent or treat infections

Some lifestyle changes can also help you manage your condition and the possible side effects from treatment:

• Eating well to help you feel better and boost your strength and energy. Your care team will provide you with nutrition goals and tips for eating during treatment.
• Exercising when appropriate to improve health and raise your mood.
• Reducing your stress with activities like exercising, yoga, or meditation.
• Lowering your risk of infections through frequent handwashing and protecting yourself from cuts and scrapes.
• Reaching out to family and friends for support.

Doctors and researchers are continuously developing and testing newer, more effective cancer treatments. These will help to boost the outlook for cancers, including CMML and CML.

If you’ve been recently diagnosed, it’s normal to feel like you need some additional support. Consider checking out some of the resources below:

• Your care team. Ask your care team about leukemia support groups or cancer support services in your area.
• The Leukemia and Lymphoma Society (LLS). The LLS has many support resources, including an online community, ways to find support groups near you, and information on financial assistance programs.
• The American Cancer Society (ACS). The ACS offers information on numerous cancer-related topics. You can also search for support resources close to you or connect through phone or video chats.
• CancerCare. CancerCare aims to provide support services to individuals impacted by cancer, free of cost.

The outlook for CMML and CML can be influenced by several factors, such as:

• your age and overall health
• the category of CMML or phase of CML that you have
• what types of genetic changes are present
• the severity of your symptoms
• which types of treatment have been tried already, if any

Keep in mind that the data and statistics used when discussing outlook do not reflect individual experiences. This information is developed based on observations of many people over long periods of time.

If you’re diagnosed with CMML or CML, your oncologist and care team will work with you to develop a treatment plan that’s tailored for your individual needs.

CMML

According to the ACS, people with CMML-0 or CMML-1 have a better outlook than those with CMML-2.

CMML can also progress to acute myeloid leukemia in about 15 to 30 percent of people, according to Cancer Research UK. While this can happen with any category of CMML, it’s more likely in people with CMML-2.

CML

The outlook for CML has greatly improved since the introduction of TKIs.

A 2016 study published in the Journal of Clinical Oncology followed the health journeys of people who had CML between the years of 1973 and 2013. The study found that the life expectancy of people with CML now approaches that of the general population — meaning that they can expect to live to what’s considered a normal lifespan.

Many people with CML will need continuing treatment over their lifetime to help keep their cancer in remission. It’s estimated that 5 to 7 percent of people with CML will still progress to the blastic phase, according to a 2020 review.

But TKI therapy can help some people with chronic CML keep their condition well controlled for long enough that they may no longer need treatment — just careful monitoring. Work closely with a doctor to determine whether you can stop treatment and what to do if you find that the condition returns and treatment is needed again.