Chronic myeloid leukemia (CML, also known as chronic myelocytic, myelogenous, or granulocytic leukemia) is classified as one of the myeloproliferative neoplasms, along with polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). (See "Overview of the myeloproliferative neoplasms".)
This group of diseases shares several distinct features:
- They are clonal disorders of hematopoiesis that arise in a hematopoietic stem or early progenitor cell.
- They are characterized by the dysregulated production of a particular lineage of mature myeloid cells with fairly normal differentiation.
- They exhibit a variable tendency to progress to acute leukemia.
- They share abnormalities of hemostasis and thrombosis.
The individual myeloproliferative neoplasms predominantly affect a single myeloid cell type, resulting in an excess of neutrophils in CML, erythrocytes in PV, and platelets in ET. However, there is considerable overlap between the clinical features as patients with CML, for example, often have thrombocytosis.
CML is almost invariably associated with an abnormal chromosome 22 known as the Philadelphia chromosome, often abbreviated as Ph, Ph(1), or Ph1 [1,2]. The Philadelphia chromosome t(9;22)(q34;q11) results in the formation of a unique gene product (BCR-ABL1), which is a constitutively active tyrosine kinase. This deregulated tyrosine kinase is implicated in the development of CML and has become a primary target for the treatment of this disorder.