CHRONIC MYELOGENOUS LEUKEMIA (CML)
Leukemias are malignant hematological neoplasms which are characterized by replacement of the bone marrow with neoplastic stem cells. Usually, leukemic cells enter the blood and cause excessive numbers of abnormal cells noted on the peripheral smear; however, sometimes the marrow is hypofunctional and leukopenia may be noted.
Chronic myelogenous leukemia (CML) accounts for 15-20% of all leukemias. It usually affects persons in the third to sixth decades of life, with a slight male predominance. Progression of this disorder is slow, and a median survival of 3 years may be expected. There are three phases, an initial chronic phase characterized by excessive production of white cells, an accelerated phase characterized by fever and bone pain, and the blast crisis, which is an accelerated phase that is not responsive to therapy and is fatal.
Symptoms include fatigue, weakness, weight loss, fever, night sweats, and anorexia. Occasionally, patients initially complain of a dragging sensation in the abdomen, which is secondary to splenomegaly. Splenomegaly with or without a friction rub is a characteristic finding on physical exam as is lymphadenopathy.
Associated laboratory abnormalities include a normocytic anemia, significant leukocytosis (predominantly neutrophils but excess amounts of basophils and eosinophils are common), thrombocytosis (noted early in the disease course), a near total lack of leukocyte alkaline phosphatase (LAP), and the characteristic presence of the Philadelphia chromosome (bcr/abl translocation) in either peripheral blood or bone marrow testing (which may also be present in acute lymphocytic leukemia). The Philadelphia chromosome is present in approximately 90% of cases of CML, and it represents a chromosomal reciprocal translocation from the long arm of chromosome 22 to chromosome 9. The presence of the Philadelphia chromosome and the lack of LAP helps distinguish CML from a leukemoid reaction. In essence, the diagnosis is made when there is the association of splenomegaly, leukocytosis (especially if immature granulocytes with basophilia and eosinophilia are present), and the Philadelphia chromosome plus the near total lack of leukocyte alkaline phosphatase. Philadelphia negative disease can be identified by FISH (Fluorescence In Situ Hybridization) or PCR on blood or bone marrow samples.
Therapy entails interferon alfa, imatinib, nilotinib, dastinib, hydroxyurea, or allogenic stem cell transplantation for chronic phase disease. Consultation with a hematologist/oncologist is essential for appropriate therapeutic decisions. Minimal residual disese (MRD) refers to the continued presence of leukemic cells that are not detected on bone marrow histology during or after treatment. Reverse transcriptase-polymerase chain reaction (RT-PCR) is an essential tool to screen for MRD in CML.