CML

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What is chronic myeloid leukemia?

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm (MPN), a chronic, progressive hematologic disorder in which there is abnormal production of blood cells by stem cells in the bone marrow. Most people with CML have a genetic mutation in which part of the genetic material from one chromosome is transferred to another chromosome. The resulting chromosome is called the Philadelphia chromosome. This chromosomal abnormality results in a great overproduction of white blood cells (WBCs) by the bone marrow. Because the WBCs are produced by an abnormal clone, they do not provide the normal function of WBCs (which is to help the body to fight infection). The overabundance of these abnormal WBCs (or leukemic cells) leaves less room for normally functioning WBCs, as well as red blood cells (RBCs; the cells that carry oxygen to tissues) and platelets (the cells that help the blood to clot) in the blood.

CML is a rare. The estimated number of new cases of CML in the United States in 2013 was 5,920. 1 The average age at CML diagnosis is approximately 64 years. CML is more common in men than women.

Symptoms

CML develops over several years. Approximately one-third to one-half of individuals have no symptoms of CML, 2 which may be discovered during routine blood work that indicates an elevated WBC count. Symptoms that may develop as CML progresses include anemia (abnormally low RBCs), which contributes to feelings of fatigue and weakness; fullness or bloating in the left upper abdominal area, or feeling full after eating a small amount of food (early satiety), that may indicate an enlarged spleen; weight loss; fever; and night sweats.2

Complications

As CML progresses, headaches; bone and joint pain; severe abdominal pain; fever; worsening anemia, splenomegaly, and night sweats; bleeding complications; and infections may occur. 2

Diagnosis

Both physical examination and a series of laboratory tests are used to determine if signs and symptoms are consistent with CML. Physical examination will determine whether the spleen is enlarged. Blood samples will be obtained for a complete blood count to examine the numbers of WBCs, RBCs, and platelets, as well as for microscopic analysis of specific characteristics of WBCs. Samples of bone marrow will be obtained to look for the Philadelphia chromosome and other chromosomal abnormalities, as well as a specific gene found in CML cells, called the BCR-ABL gene. 2,3

If these tests confirm a diagnosis of CML, the laboratory tests are used to determine how aggressive it is, or the phase of the disease. There are three phases of CML: chronic phase, which is the earliest phase and typically associated with the best responses to treatment; accelerated phase, where the disease is becoming more aggressive; and blastic phase, where CML is advanced and its effects are severe and life-threatening.

Current Treatments

The primary treatment for CML, particularly when diagnosed as chronic phase, is targeted therapy, 2-4 which acts on specific malignant cells, without harming normal cells. Targeted therapies belong to a class of drugs known as tyrosine kinase inhibitors (TKIs). TKIs for CML target a cellular protein made by the BCR-ABL gene, called BCR-ABL. TKIs used as front-line therapy for chronic phase CML include imatinib, dasatinib, and nilotinib. The choice of TKI for initial therapy may be based on a variety of factors, including the patient’s age, concurrent medical conditions, and the aggressiveness of CML.5 Dasatinib and nilotinib may be used successively as subsequent therapies in patients who stop responding to or cannot tolerate a previous TKI used for treatment. Bosutinib may be used in patients who have been treated with and not responded to imatinib, dasatinib, and nilotinib, and ponatinib may be used after all other treatments, or if a genetic mutation occurs following treatment with the other TKIs.4,6

In patients with chronic-phase CML who do not respond to or cannot tolerate TKIs, allogeneic stem cell transplantation (alloSCT) may be recommended.4 AlloSCT involves administration of high- or reduced-intensity regimens of chemotherapy or radiation to impair the bone marrow’s ability to make new stem cells, followed by transplantation of stem cells from a healthy donor.

Patients with accelerated phase or blastic phase CML may also be treated with TKIs, depending on their previous exposure to them. AlloSCT may be recommended in patients who do not respond to TKIs. Sometimes, chemotherapy may be required prior to alloSCT. 4

The safety and effectiveness of other new drugs for the treatment of CML are currently being evaluated in clinical trials.

References

  1. American Cancer Society. Cancer Facts and Figures 2013. Atlanta: American Cancer Society; 2013.
  2. Jabbour E, Kantarjian H. Chronic myeloid leukemia: 2012 update on diagnosis, monitoring, and management. Am J Hematol. 2012;87:1038-1045.
  3. Cortes J, Kantarjian H. How I treat newly diagnosed chronic phase CML. Blood. 2012;120:1390-1397.
  4. Baccarani M, Deininger M, Gianantonio R, Hochhaus A, Soverini S, Apperley JF, et al. European LeukemiaNet recommendations for the management of chronic myeloid leukemia: 2013. Blood. 2013;122:872-884.
  5. Hughes T, White D. Which TKI? An embarrassment of riches for chronic myeloid leukemia patients. Hematology Am Soc Hematol Educ Program. 2013;2013:168-175.
  6. American Cancer Society. Leukemia–Chronic myeloid (myelogenous). www.cancer.org/cancer/leukemia-chronicmyeloidcml/d… Last update December 30, 2013. Accessed January 26, 2014.