Chronic myelomonocytic leukemia (CMML) diagnosis

Chronic Myelomonocytic Leukemia (CMML) is difficult to diagnose and typically involves a series of repeated tests, including blood and bone marrow tests.

Your doctor usually can't confirm a diagnosis of CMML with one lab test result that shows abnormal blood counts. Instead, they will monitor you over time with repeated lab tests that show abnormal blood counts. This is done to rule out other diagnoses.

If there is uncertainty in the diagnosis, it is important to consider getting a second opinion.

Tests your doctor may use to diagnose CMML

Blood tests measure the number of red and white blood cells and platelets in the blood; bone marrow tests measure the fluid and tissue in your marrow.

Bone marrow and blood testing

Bone marrow testing involves two steps usually done at the same time in a doctor's office or a hospital:

• A bone marrow aspiration to remove a liquid marrow sample
• A bone marrow biopsy to remove a small amount of bone filled with marrow

Learn more about bone marrow tests.

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A “hematopathologist”—a specialist who studies blood cell diseases by examining samples of blood cells, bone marrow cells, and other tissues— looks for the following criteria to identify CMML:

• Persistent high levels of monocytes in the blood
• No evidence of a Philadelphia chromosome, which is seen in a similar disease known as “chronic myeloid leukemia" (CML). This can be determined based on a blood test.
• Less than 20 percent of blast cells in the blood and bone marrow
• Abnormalities in one or more types of precursor cells that develop into red blood cells, certain types of white blood cells, or platelets

Cytogenetic and molecular abnormalities

Cytogenetic abnormalities refer to abnormal changes in chromosomes, which may include broken, missing, rearranged, or extra chromosomes. Approximately 20 to 30 percent of CMML patients have chromosomal abnormalities, some of which can affect prognosis and treatment.

Molecular abnormalities refer to abnormal changes in genes. These abnormalities are known as gene mutations. Mutations that are acquired and not inherited are called "somatic mutations." In CMML, almost 90 percent of patients exhibit one or more somatic mutations. Some molecular abnormalities can affect prognosis and treatment.

Diagnosing CMML subtypes

Most people diagnosed with CMML have one of three different subtypes of CMML based on the percentage of blast cells ("blasts") in the blood and bone marrow.

Doctors use a classification system developed by the World Health Organization (WHO).

In most healthy people, there are no blasts in the blood and fewer than 5 percent in the bone marrow.

In addition, based on the white blood cell (WBC) count, CMML can be grouped into two subtypes:

• A dysplastic type (MD-CMML) defined by WBC < 13x10⁹/L (liters)
• A proliferative type (MP-CMML) defined by WBC ≥ 13x10⁹/L