Most people diagnosed with chronic myelomonocytic leukemia (CMML) have one of two different subtypes of CMML. Doctors classify CMML subtypes by 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 2001. The two subtypes are:
- CMML-1, which has less than 5 percent blasts in the blood and less than 10 percent blasts in the bone marrow
- CMML-2, which has more than 5 percent but less than 20 percent blasts in the blood and 10 to 20 percent blasts in the bone marrow
Most healthy individuals have less than 5 percent blast cells in their developing bone marrow cells.