Can CML progress to AML (Acute Myelogenous Leukemia)?

For the most part, the simple answer is "no", CML does not progress to AML (there have been reported cases over the years of CML patients developing AML, however the occurrence is extremely rare). While blast crisis (BC) CML is similar to the acute leukemias, there are still differences. BC in CML can be delineated into two different types: myeloid blast crisis which closely resembles AML and lymphoid blast crisis which closely resembles ALL. 

CML progresses through phases that are different from the acute leukemias. CML is differentiated into Chronic Phase, Accelerated Phase and Blast Phase.

Most patients are diagnosed with CML when in the chronic phase of the disease. If those in chronic phase go untreated, they may rapidly progress to the accelerated and blast phases of the disease. All efforts should be made to manage CML while in the chronic phase. 

Each phase of CML can be described and differentiated by the number of immature cells found in the bone marrow. In Chronic phase, an individual's immature cells (called blasts) make up less than 10% of their bone marrow. In the Accelerated phase of CML, the amount of immature cells in the bone marrow comprise 10% to 30% of the total blood cells. In the Blast phase of CML, greater than 30% of the blood cells in the bone marrow are immature cells. 

If a patient presents with a high number of immature cells in the bone marrow, the determination of what type of leukemia he or she has may not be readly available. At times, bone marrow material or blood from a past blood test can be used to identify the presence of the Philadelphia chromosome, or the BCR-ABL translocation. While very rare cases of some acute lymphoblastic leukemias can have the Phladelphia chromosome present, the vast majority do not. In these rare individuals, an oncologic pathologist will be able to see slight variations in the breakpoint region, that identify these as atypical Philadelphia chromosome findings and will warrant additional information to diagnose correctly.

Most pathologists will also look at the remaining normal cells in the patients blood and bone marrow. In CML you would likely see a large number of neutrophils and basophils. In patients with acute leukemias, the blood tests would show that the basophils are not as elevated and that the distribution of cell types would look more like a normal array. This knowledge assists in the determination of leukemia type. Blast crisis in a CML patient is extremely dangerous and all efforts should be made to avoid a patient's progression to this phase.