Juvenile myelomonocytic leukemia (JMML) diagnosis

Diagnosing juvenile myelomonocytic leukemia (JMML) usually involves ruling out other similar diseases such as chronic myelomonocytic leukemia (CMML) and chronic myeloid leukemia (CML), especially if your child is older than 6 years.  

The tests doctors commonly used to diagnose JMML include: 

• Blood tests
• Bone marrow aspiration and biopsy
• Cytogenetic and molecular tests that look for cytogenetic (chromosomal) and molecular abnormalities (gene mutations) in the cancer cells 

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Diagnostic criteria for JMML

Category 1 (all of the following): 

• Presence of an enlarged spleen
• A persistent elevated monocyte count in the blood greater than 1x109/L, which is equivalent to 1,000 monocytes per microliter of blood (1,000/µl)
• The absence of the Philadelphia chromosome (Ph chromosome) and the BCR-ABL1 gene rearrangement. The Ph chromosome is an abnormality of chromosome 22 found in the marrow and blood cells of patients with CML.
• Less than 20 percent blast cells circulating in the blood and present in the bone marrow 

Category 2 (at least one of the following): 

• Somatic (change in DNA that happens after conception) mutation in PTPN11, KRAS, or NRAS genes
• Clinical diagnosis of neurofibromatosis type 1 (NF1) or NF1 gene mutation 
• Germline CBL gene mutation 

Category 3 (if criteria from Category 2 are not met, two of the following are acceptable): 

• Monosomy 7 (only one chromosome from a pair) or any other chromosomal abnormality
• Higher levels of hemoglobin F than is normal for the age of the patient
• Myeloid precursors (predecessor of red blood cells, platelets, and some types of white blood cells) in the blood
• Granulocyte-macrophage colony-stimulating factor (GM-CSF) hypersensitivity in colony assay
• Hyperphosphorylation of STAT5 

Cytogenetic (Chromosomal) and molecular abnormalities 

Nearly all JMML patients have an abnormality in a specific gene or chromosome. A mutation in the genes of the RAS pathway is detected in more than 95 percent of JMML patients. Monosomy 7 and other chromosome 7 abnormalities occur in approximately 25 percent to 30 percent of patients.