CML is the most common disorder of the MPN group. It is characterized by a slow but progressive production of clonal myeloid cells, leading to hypercellularity of both the bone marrow and peripheral blood. Along with increasing myeloid hematopoietic activity in the bone marrow, cell production also occurs within the spleen and liver via extramedullary hematopoiesis, leading to splenomegaly. Extramedullary masses (tumors) in CML have a green coloration due to the presence of myeloperoxidase. These tumors are appropriately referred to as "chloromas."
CML has three distinct phases: chronic, accelerated, and blast phases. Usually when a patient is diagnosed during the chronic phase, the prognosis is good since response to therapy can be successful. When CML has progressed into accelerated or blast phase (blastic leukemia), treatment can be difficult and survival rates decline to around six months. It can take years, with effective treatment, for CML to progress to the accelerated and blast phases. CML is associated with an eventual transformation into acute myeloid leukemia (AML) or acute lymphoblastic leukemia (ALL).
Patients report a variety of symptoms that typically include:
- Difficultly breathing
- Weight loss or appetite loss
- Night sweats
- Bone/joint pain
- Bleeding complications
- Susceptibility to infections
The incidence of CML increases with age and most commonly occurs in patients over 70 years of age.