Chronic myelogenous leukemia

(medicine) A form of leukemia in which immature granulocytes are predominant and the life expectancy is 1-20 years or more.

Key Terms: Accelerated phase, Basophil, Blast, Bone marrow, Chemotherapy, Chronic phase, Hypercellular, Leukapheresis, Philadelphia (Ph) chromosome, Remission.

Definition

Chronic myelocytic leukemia (CML) is a cancer of white blood cells in which too many white blood cells are made in the bone marrow. Chronic myelogenous leukemia and chronic myeloid leukemia are other names for CML and refer to the identical disease. Depending on the type of white blood cell that is involved, chronic leukemia can be classified as chronic lymphocytic leukemia or chronic myelocytic leukemia. In chronic myelocytic leukemia, there is an increased proliferation of white blood cells called granulocytes.

Description

Chronic leukemia is a cancer that starts in the blood cells made in the bone marrow. The bone marrow is the spongy tissue found in the large bones of the body. The bone marrow makes precursor cells called "blasts" or "stem cells" that mature into different types of blood cells. Unlike acute leukemias, in which the process of maturation of the blast cells is interrupted, in chronic leukemias, the cells do mature and only a few remain as immature cells. However, even though the cells appear normal, they do not function as normal cells.

The different types of cells produced in the bone marrow are red blood cells (RBCs), which carry oxygen and other materials to all tissues of the body; white blood cells (WBCs), which fight infection; and platelets, which play a part in the clotting of the blood. The white blood cells can be further subdivided into three main types: the granulocytes, monocytes, and the lymphocytes.

The granulocytes, as their name suggests, have granules (particles) inside them. These granules contain special proteins (enzymes) and several other substances that can break down chemicals and destroy microorganisms such as bacteria. Monocytes are also important in defending the body against pathogens.

The lymphocytes form the third type of white blood cell. There are two main types of lymphocytes: T lymphocytes and B lymphocytes. They have different functions within the immune system. The B cells protect the body by making antibodies. Antibodies are proteins that can attach to the surfaces of bacteria and viruses. This attachment sends signals to many other cell types to come and destroy the antibody-coated organism. The T cell protects the body against viruses. When a virus enters a cell, it produces certain proteins that are projected onto the surface of the infected cell. The T cells can recognize these proteins and produce certain chemicals (cytokines) that are capable of destroying the virus-infected cells. In addition, the T cells can destroy some types of cancer cells.

Chronic leukemias develop very gradually. The abnormal lymphocytes multiply slowly, but in a poorly regulated manner. They live much longer than normal cells and thus their numbers build up in the body. The two types of chronic leukemias can be easily distinguished under the microscope. Chronic lymphocytic leukemia (CLL) involves the T or B lymphocytes. In chronic myelocytic leukemia (CML), the cells affected are the granulocytes. In addition, CML involves abnormalities of both the blood platelets, structures that help blood to clot, and the red blood cells, the blood cells that carry oxygen.

Very rarely will CML appear in children. Juvenile CML is a distinct disease of children younger than 14 years of age. There is a decrease in the number of blood platelets, substances that help the blood to clot. And there is an increase in certain white blood cells.!

Demographics

Slightly more men than women are affected by CML. The average patient is between 50 and 60 years of age. However, CML can affect people of any age. Chronic leukemias account for 1.2% of all cancers. Chronic myelocytic leukemia is generally seen in people in their mid-40s. According to the estimates of the American Cancer Society (ACS), approximately 4,400 new cases of leukemia were diagnosed in the year 2000, 2,600 in men and 1,800 in women. Between 1973 and 1991, the rate at which CML appeared in the United States decreased slightly.

Causes and Symptoms

People exposed to nuclear and other radiation are at increased risk for CML. Thus, people who have had higher exposure to radiation for medical reasons are at increased risk of developing this cancer. Parents with CML do not have children who are more than normally likely to develop CML. However, it is possible that people whose immune system exhibits certain characteristics are at increased risk for the disease.

CML develops in a two- or three-stage progression. First, the chronic phase appears. Between 60 and 80 percent of patients next exhibit the symptoms of what is called the accelerated phase. The final stage of CML is the terminal blastic phase.

Symptoms of chronic phase CML appear in 60%–85% of patients. This means 15% to 40% of all the people diagnosed with CML have no symptoms at all and are diagnosed with the disease only because of the results of a routine blood test. Patients who do have symptoms most frequently find themselves to have fatigue, weight loss, or pain. Some patients have a mass of tissue or an enlarged liver that the doctor is able to feel. Some patients experience strokes, visual problems, a lowering of alertness or responsiveness, priapism, and ringing in the ear. Many patients in accelerated phase CML have no specific symptoms. However, fever, weight loss, and night sweats may appear.

Patients with terminal, blastic phase CML often experience symptoms. There may be fever, weight loss, night sweats, and bone pain. Many patients develop infections. Many have anemia (low counts of red blood cells) and many bleed easily.

Diagnosis

There are no screening tests available for chronic leukemias. The detection of these diseases may occur by chance during a routine physical examination.

People who have CML have an unusually high number of white blood cells. Somewhat less than half of these people also have high numbers of blood platelets. Most patients have mild anemia. The composition of the bone marrow in CML patients also differs from that of a healthy person. The marrow is described as being hyper-cellular. This means that the number of cells present in the bone marrow is unusually great.

If the doctor has reason to suspect leukemia, he or she will conduct a very thorough physical examination to look for enlarged lymph nodes in the neck, underarm, and pelvic region. Swollen gums, an enlarged liver or spleen, bruises, or pinpoint red rashes all over the body are among the signs of leukemia. Urine and blood tests may be ordered to check for microscopic amounts of blood in the urine and to obtain a complete differential blood count. This count will give the numbers and percentages of the different cells found in the blood.

Standard imaging tests such as x rays, computed tomography scans (CT scans), and magnetic resonance imaging (MRI) may be used to check whether the leukemic cells have invaded other organs of the body, such as the bones, chest, kidneys, abdomen, or brain.

Many doctors consider the presence of the Philadelphia (Ph) chromosome to be a crucial factor in the diagnosis of CML. The Ph chromosome is formed if some of the genetic material in two specific parts of two specific genetic units, called chromosomes, have exchanged some content in a particular way and created an arrangement of genetic material characteristic of CML patients.

Laboratory findings indicate when a patient enters the accelerated phase of CML. There may be more than 15% blasts (immature cells) in the blood. Alternately, the accelerated phase has started when more than 30% of the blood may be composed of a combination of blasts and promyelocytes. Promyelocytes are immature granulocytes. Another marker for the start of the accelerated phase is when the blood contains more than 20% of another white blood cell, called a basophil. Finally, the accelerated phase may be heralded by there being more than 100,000,000,000 platelets per liter of blood. The terminal, blastic phase of CML is heralded by measurements of 30% or more of blasts in either the bone marrow or the blood.

Clinical Staging, Treatments, and Prognosis

Staging

Several different staging systems are in use. Most of these make use of the fact that a number of factors relevant to patients with CML say something about the patient's prognosis. Among these factors are the patient's age, the white blood cell count, the platelet count, the percentage of blast cells and basophil cells in either the blood or the bone marrow, the size of the liver, the size of the spleen, population of red blood cells that have a central portion called a nucleus, and the evolution of certain cell clones.

Treatment

It is very fortunate that several years ago the American Society of Hematology convened an Expert Panel on Chronic Myeloid Leukemia. This panel reviewed available therapies and published its findings in 1999. The findings were rigorously based upon evidence provided by the best research. The panel, comprised of top doctors from around the world, carefully sifted through all of the studies on treatment for CML and put aside all those studies performed with questionable methodology. This is a most important document relevant to CML therapy.

Since the publication of the findings of the expert panel, however, a new medicine has demonstrated great success in studies. This new medicine is known as STI571, Imatinib mesylate, or Gleevec. Since Gleevec was such a new drug in 2001, few studies have been conducted to evaluate its long-term effects. Furthermore, researchers have not had an opportunity to view the effects of imatinib mesylate over a period of five, 10, or 20 years.

In terms of CML therapy, the situation in 2001 was the following: physicians have the reliable report of the Expert Panel and a little bit of new information about a new medication. How the Expert Panel's findings and this new information should be integrated with the results of recent studies of imatinib mesylate is an issue that cancer doctors are currently resolving.

The Expert Panel looked at treatment of the chronic phase of CML. One therapy examined by the panel is busulfan (BUS). Another is hydroxyurea (HU). Both BUS and HU are chemotherapy medications. Studies have demonstrated that CML patients in chronic phase given HU live longer than patients given BUS.

Another therapy examined by the expert panel is interferon-alpha. Interferon is a chemical normally made in the cells of the body. It helps protect the body against viruses and also seems to have some effect against certain cancers. The interferon used as medicine is a laboratory-manufactured copy of the interferon produced by the body. The Expert Panel concluded that patients in chronic phase CML who have received interferon live longer than those given HU or BUS. This conclusion applies, in particular, to patients who have had little prior treatment for CML, who start interferon treatment soon after diagnosis, and who have certain other characteristics. However, side effects of interferon therapy are greater than those of therapy with HU or BUS. Patients who develop the side effects of interferon may feel like they have the flu. Patients receiving interferon seem to do better if they also receive chemotherapy with either HU or a medicine called Ara-C, or cytarabine.

Bone marrow transplantation (BMT) is an effective treatment for CML. In BMT, the patient's diseased bone marrow is replaced with healthy marrow. There are two ways of doing a bone marrow transplant. In an allogeneic bone marrow transplant, healthy marrow is taken from another person (donor) whose tissue is either the same or very closely resembles the patient's tissues. The donor may be a twin, a sibling, or a person who is not related at all. First, the patient's bone marrow is destroyed with very high doses of chemotherapy and radiation therapy. To replace the destroyed marrow, healthy marrow from the donor is given to the patient.

In the second type of bone marrow transplant, called an autologous bone marrow transplant, some of the patient's own marrow is taken out and treated with a combination of anticancer drugs to kill all the abnormal cells. This marrow is then frozen to save it. The marrow remaining in the patient's body is then destroyed with high dose chemotherapy and radiation therapy. Following that, the patient's own marrow that was frozen is thawed and given back to the patient.

Allogeneic BMT may be used soon after diagnosis or after a patient has been treated with interferon or chemotherapy. The Expert Panel found that carefully designed, well-controlled, randomized studies have not been conducted on BMT therapy for CML. In the studies that do exist, scientists performed BMT on a group of patients and then observed the results. These studies show that BMT may lead to long-term remission. Remission is achieved if the disease becomes diminished for a period. Patients appear to live longer if they received chemotherapy followed by BMT. But the Expert Panel cautions that the results of these observational studies cannot be relied upon. One problem with them might be, for example, that the patients chosen to receive BMT might have started out being healthier than patients who did not receive BMT. The side effects of BMT may be severe, and a large number of CML patients receiving BMT die as a direct result of the BMT.

Therefore, one important consideration when BMT is being considered is whether the conditions under which the individual patient might receive BMT are favorable. In other words, is a very suitable marrow donor available? Is the patient within two years of CML diagnosis? It is important that patients understand clearly the ptential benefits and risks of BMT. One comment made by the Expert Panel is that younger patients who hope to live a very long time after CML diagnosis are more likely to benefit from allogeneic BMT. Autologous BMT has not achieved superior long-term results.

The recent studies of imatinib mesylate found it very effective in two groups of CML patients. One group was made up of patients who had unsuccessful results with interferon alfa therapy. The other group of CML patients studied were in the blast phase of the disease. Both studies found the medication to be effective and well tolerated. However, studies reporting on the effectiveness of imatinib mesylate over periods of five years or longer were not yet available in 2001.

Because leukemia cells can spread to all the organs via the blood stream and the lymph vessels, surgery is not considered an option for treating the leukemias.

The Expert Panel was careful to state that patient preferences should be taken into account as a treatment plan is developed. No approach to CML therapy is perfect. Each provides some benefit and is accompanied by certain side effects and risks. Which therapy or therapies is best for each individual patient depends upon on certain facts, such as the age of the patient and whether the patient is suffering from illnesses other than CML. In addition, the Expert Panel explains that the personal preferences of each patient are an important consideration. For example, some patients would rather avoid potential severe side effects and would be willing to give up the potential of living another few months or years. Other patients would be entirely unwilling to accept this way of looking at risks and benefits. It is important that health care professionals educate patients as to what treatment options are available and the perfections and imperfections associated with each. The opinions of each patient should be an important factor in deciding which treatment is best for that patient.

In the accelerated and blastic phase of CML, aggressive chemotherapy may be given. Combination chemotherapy, in which multiple drugs are used, is more effective than using a single drug for the treatment. Interferon and BMT may be used, although results are not as good as for patients in the chronic phase of CML.

It should be mentioned that during treatment the doctor may order a procedure called leukapheresis. This lowers the numbers of white blood cells circulating in the patient's body. Also, either before or after therapy, it may be necessary to provide the patient with a transfusion of blood platelets. In addition, antibiotics are often used to help prevent infection in leukemia patients.

Prognosis

The most important factor in determining the likeli-hood that a patient receiving interferon therapy will achieve long-term survival is whether there is a positive response to interferon-alfa. Although experience with imatinib mesylate is being gathered in studies, this drug remains so new that doctors do not know what effect it will have on the prognosis of CML patients. Once the threat of transplantation-related complications has passed, patients receiving BMT may achieve longer survival than patients receiving interferon therapy.

Before the discovery of modern therapies, patients often spent between three-and-a-half and five years in the chronic phase. Then some patients entered an accelerated phase, from which most died within 18 months. Once patients were in the terminal, blastic phase most died within six months. However, all of this has changed with the arrival of newer therapeutic techniques. Just as many patients used to die from heart attack while similar patients may now live for decades, so cancer patients are achieving longer lives.

Coping With Cancer Treatment

Cancer patients need supportive care to help them come through the treatment period with physical and emotional strength in tact. Many patients experience feelings of depression, anxiety, and fatigue, and many experience nausea and vomiting during treatment. Studies have shown that these can be managed effectively if discussed with a doctor.

Questions to Ask the Doctor

• How can I obtain supportive care so I come through this not only alive but with my family and emotional life intact?
• What sort of benefit and what sort of side effects might each of the available treatment options bring?
• Would you please inform me about the treatment options and let me tell you about the priorities in my life so I can participate in forming a treatment plan?
• What is my prognosis?
• Are blasts present?
• Has complete remission or partial remission been achieved?
• What can I do to lower my risk of infection during chemotherapy?

Prevention

Although some cancers are related to known risk factors, such as smoking, in leukemias, there are no definitive risk factors. Therefore, at the present time, there is no way known to prevent the leukemias from developing. People who are at an increased risk for developing leukemia because of proven exposure to ionizing radiation, the organic liquid benzene, or people who have a history of other cancers of the lymphoid system (Hodgkin's lymphoma) should undergo periodic medical checkups.

Resources

Books

Braunwald, Eugene, et al. Harrison's Principles of Internal Medicine. 15th ed. New York: McGraw-Hill, 2001.

Humes, H. David, et al. Kelley's Textbook of Internal Medicine. 4th ed. Philadelphia: Lippincott Williams & Wilkins, 2000.

Pazdur, Richard, et al. Cancer Management: A Multidisciplinary Approach: Medical, Surgical, & Radiation Oncology. 4th ed. Melville, NY: PRR, 2000.

Periodicals

Drucker B. J., et al. "Activity of a specific inhibitor of the BCR-ABL tyrosine kinase in the blast crisis of chronic myeloid leukemia and acute lymphoblastic leukemia with the Philadelphia chromosome." New England Journal of Medicine 344 (2001): 1038-1042.

Drucker, B. J., et al. "Efficacy and safety of a specific inhibitor of the BCR-ABL tyrosine kinase in chronic myeloid leukemia." New England Journal of Medicine 344 (2001): 1031-1037.

Silver, Richard T., et al. "An evidence-based analysis of the effect of busulfan, hydroxyurea, interferon, and allogeneic bone marrow transplantation in treating the chronic phase of chronic myeloid leukemia: developed for the American Society of Hematology." Blood, 94 (1999): 1517-1536.

Organizations

The American Cancer Society publishes useful texts, which include: Adult Chronic Leukemia - Overview, Leukemia - Adult Chronic: Treatment, Leukemia - Adult Chronic: Detection and Symptoms, Leukemia: Adult Chronic FAQ [Frequently Asked Questions], and Leukemia - Adult Chronic: Prevention & Risk. Telephone:1-800-ACS-2345. Web site: .

The Leukemia & Lymphoma Society (Formerly Leukemia Society of America) publishes useful texts available through the Internet or by mail. Some publications include: Chronic Myelogenous Leukemia (CML), Choosing a Specialist. Choosing a Treatment Facility, Making Intelligent Choices About Therapy, Understanding Blood Counts, Patient Aid Program, and Family Support Group. Telephone:1-800-955-4572. Web site: .

The National Cancer Institute publishes useful texts available through the Internet or by mail, and answers questions by telephone. Some publications include: Leukemia, What You Need to Know About Leukemia, PDQ - Treatment Patients: Chronic Myelogenous Leukemia, and Complementary & Alternative Therapies for Leukemia, Lymphoma, Hodgkin's Disease, & Myeloma. Telephone: 1-800-4CANCER. Web site: .

National Coalition for Cancer Survivorship. 1010 Wayne Avenue, 7th Floor, Silver Spring, MD 20910-5600. Telephone: (301) 650-9127 and (877)NCCS-YES [877-622-7937). Web site: .

—Lata Cherath, Ph.D.; Bob Kirsch

Cell-mediated lympholysis.

Chronic myelogenous leukemia
Classification and external resources
The Philadelphia chromosome as seen by metaphase FISH.
ICD-10	C92.1
ICD-9	205.1
ICD-O:	M9875/3
DiseasesDB	2659
MedlinePlus	000570
eMedicine	med/371
MeSH	D015464

Chronic myelogenous (or myeloid) leukemia (CML), also known as chronic granulocytic leukemia (CGL), is a cancer of the white blood cells. It is a form of leukemia characterized by the increased and unregulated growth of predominantly myeloid cells in the bone marrow and the accumulation of these cells in the blood. CML is a clonal bone marrow stem cell disorder in which proliferation of mature granulocytes (neutrophils, eosinophils, and basophils) and their precursors is the main finding. It is a type of myeloproliferative disease associated with a characteristic chromosomal translocation called the Philadelphia chromosome. It is now treated with imatinib and other targeted therapies, which have dramatically improved survival.

Contents 1 Signs and symptoms 2 Diagnosis 3 Pathophysiology 4 Classification 4.1 Chronic phase 4.2 Accelerated phase 4.3 Blast crisis 5 Treatment 5.1 Chronic phase 6 Prognosis 7 Epidemiology 8 References 9 External links

Signs and symptoms

Patients are often asymptomatic at diagnosis, presenting incidentally with an elevated white blood cell count on a routine laboratory test. In this setting, CML must be distinguished from a leukemoid reaction, which can have a similar appearance on a blood smear. Symptoms of CML may include: malaise, low-grade fever, gout, increased susceptibility to infections, anemia, and thrombocytopenia with easy bruising (although an increased platelet count (thrombocytosis) may also occur in CML). Splenomegaly may also be seen.^[1][2]

Diagnosis

CML is often suspected on the basis on the complete blood count, which shows increased granulocytes of all types, typically including mature myeloid cells. Basophils and eosinophils are almost universally increased; this feature may help differentiate CML from a leukemoid reaction. A bone marrow biopsy is often performed as part of the evaluation for CML, but bone marrow morphology alone is insufficient to diagnose CML.^[2][3]

Ultimately, CML is diagnosed by detecting the Philadelphia chromosome. This characteristic chromosomal abnormality can be detected by routine cytogenetics, by fluorescent in situ hybridization, or by PCR for the bcr-abl fusion gene.^[2]

Controversy exists over so-called Ph-negative CML, or cases of suspected CML in which the Philadelphia chromosome cannot be detected. Many such patients in fact have complex chromosomal abnormalities which mask the (9;22) translocation, or have evidence of the translocation by FISH or RT-PCR in spite of normal routine karyotyping.^[4] The small subset of patients without detectable molecular evidence of bcr-abl fusion may be better classified as having an undifferentiated myelodysplastic/myeloproliferative disorder, as their clinical course tends to be different from patients with CML.^[5]

Pathophysiology

CML was the first malignancy to be linked to a clear genetic abnormality, the chromosomal translocation known as the Philadelphia chromosome. This chromosomal abnormality is so named because it was first discovered and described in 1960 by two scientists from Philadelphia, Pennsylvania: Peter Nowell of the University of Pennsylvania and David Hungerford of the Fox Chase Cancer Center at Temple University. ^[6]

In this translocation, parts of two chromosomes (the 9th and 22nd by conventional karyotypic numbering) switch places. As a result, part of the BCR ("breakpoint cluster region") gene from chromosome 22 is fused with the ABL gene on chromosome 9. This abnormal "fusion" gene generates a protein of p210 or sometimes p185 weight (p is a weight measure of cellular proteins in kDa). Because abl carries a domain that can add phosphate groups to tyrosine residues (a tyrosine kinase), the bcr-abl fusion gene product is also a tyrosine kinase.^[1][3]

The fused bcr-abl protein interacts with the interleukin 3beta(c) receptor subunit. The bcr-abl transcript is continuously active and does not require activation by other cellular messaging proteins. In turn, bcr-abl activates a cascade of proteins which control the cell cycle, speeding up cell division. Moreover, the bcr-abl protein inhibits DNA repair, causing genomic instability and making the cell more susceptible to developing further genetic abnormalities. The action of the bcr-abl protein is the pathophysiologic cause of chronic myelogenous leukemia. With improved understanding of the nature of the bcr-abl protein and its action as a tyrosine kinase, targeted therapies have been developed (the first of which was imatinib mesylate) which specifically inhibit the activity of the bcr-abl protein. These tyrosine kinase inhibitors can induce complete remissions in CML, confirming the central importance of bcr-abl as the cause of CML.^[3]

Classification

CML is often divided into three phases based on clinical characteristics and laboratory findings. In the absence of intervention, CML typically begins in the chronic phase, and over the course of several years progresses to an accelerated phase and ultimately to a blast crisis. Blast crisis is the terminal phase of CML and clinically behaves like an acute leukemia. One of the drivers of the progression from chronic phase through acceleration and blast crisis is the acquisition of new chromosomal abnormalities (in addition to the Philadelphia chromosome).^[1] Some patients may already be in the accelerated phase or blast crisis by the time they are diagnosed.^[2]

Chronic phase

Approximately 85% of patients with CML are in the chronic phase at the time of diagnosis. During this phase, patients are usually asymptomatic or have only mild symptoms of fatigue or abdominal fullness. The duration of chronic phase is variable and depends on how early the disease was diagnosed as well as the therapies used. Ultimately, in the absence of curative treatment, the disease progresses to an accelerated phase.^[2]

Accelerated phase

Criteria for diagnosing transition into the accelerated phase are somewhat variable; the most widely used criteria are those put forward by investigators at M.D. Anderson Cancer Center,^[7] by Sokal et al.,^[8] and the World Health Organization.^[5][9] The WHO criteria are perhaps most widely used, and define the accelerated phase by any of the following:

• 10–19% myeloblasts in the blood or bone marrow
• >20% basophils in the blood or bone marrow
• Platelet count <100,000, unrelated to therapy
• Platelet count >1,000,000, unresponsive to therapy
• Cytogenetic evolution with new abnormalities in addition to the Philadelphia chromosome
• Increasing splenomegaly or white blood cell count, unresponsive to therapy

The patient is considered to be in the accelerated phase if any of the above are present. The accelerated phase is significant because it signals that the disease is progressing and transformation to blast crisis is imminent.^[5]

Blast crisis

Blast crisis is the final phase in the evolution of CML, and behaves like an acute leukemia, with rapid progression and short survival.^[2] Blast crisis is diagnosed if any of the following are present in a patient with CML:^[10]

• >20% myeloblasts or lymphoblasts in the blood or bone marrow
• Large clusters of blasts in the bone marrow on biopsy
• Development of a chloroma (solid focus of leukemia outside the bone marrow)

Treatment

Chronic phase

Chronic phase CML is treated with inhibitors of tyrosine kinase, the first of which was imatinib mesylate (marketed as Gleevec or Glivec; previously known as STI-571). In the past, antimetabolites (e.g. cytarabine, hydroxyurea), alkylating agents, interferon alfa 2b, and steroids were used, but these drugs have been replaced by imatinib. Imatinib was approved by the United States FDA in 2001 and specifically targets BCR/abl, the constitutively activated tyrosine kinase fusion protein caused by the Philadelphia chromosome translocation. It is better tolerated and more effective than previous therapies. The IRIS study is an international study that compared interferon/cytarabine combination with imatinib. Long term follow up demonstrating the superiority of imatinib regimens is clear cut. However, the data of this study which allowed cross-over to Glivec has never been presented in an intent to treat analysis. The question remains as to whether Glivec treatment following cytarabine/interferon is better than Glivec alone in the long term is left unanswered. Bone marrow transplantation was also used as initial treatment for CML in younger patients before the advent of imatinib, and while it can often be curative, there was a high rate of transplant-related mortality. The transplant-related mortality rate in the present is less than 5%. ^[3]

As described below, a number of newer drugs are being used to treat the minority of patients who develop imatinib resistance. However, trials such as SPIRIT 2 are also underway to evaluate these newer drugs as 'upfront' therapy for patients with newly diagnosed chronic phase CML.

To overcome imatinib resistance and to increase responsiveness of TK inhibitors, two novel agents have been developed. The first, dasatinib, is a TK inhibitor that blocks several oncogenic proteins and has been approved by the US FDA to treat CML patients who are either resistant to or intolerant of imatinib in 2007. Another TK inhibitor, nilotinib, is also approved by the US FDA for the same indication. Nilotinib is designed to bind more tightly than imatinib to the Bcr-Abl abnormal fusion protein responsible for chronic myeloid leukemia. Dasatanib is being compared with Imatinib for first line therapy in the SPIRIT II trial being undertaken in the United Kingdom. Study on the combination of alpha Interferon with Imatanib is currently recruiting in higher risk patients in chronic phase CML.

Dasatanib and nilotinib failed to overcome the imatinib resistance caused by the T315I mutation. All current treatments for this mutation are experimental. Recently Chemgenex released results of their open label Phase 2/3 study (CGX-635-CML-202) which investigated the use of omacetaxine, administered subcutaneously in CML patients who had failed imatinib and who have the highly drug resistant T315I kinase domain mutation.

Dr. Jorge Cortes, MD, Professor of Medicine and Deputy Chair in the Department of Leukemia at The University of Texas, MD Anderson Cancer Center, a lead investigator in the study, presented the data. Dr. Cortes said, “It appears that omacetaxine was well tolerated in this study and durable hematological and cytogenetic responses were observed in some CML patients with the T315I mutation.” He added that “Several novel drugs have already been investigated in this difficult-to-treat population, but they have not had a reasonable risk:benefit ratio. These results suggest that omacetaxine may represent the first viable treatment option for this population of patients who currently have no established treatment options.”

Stem cell transplantation is an option for those patients who developed T315I mutation.^[11][12]

In 2005 favourable results of vaccination were reported with the BCR/abl p210 fusion protein in patients with stable disease, with GM-CSF as an adjuvant.^[13]

Prognosis

In one analysis of several clinical studies, three different risk groups were identified based on a prognostic scoring system that includes several variables: age, spleen size, blast count, platelet count, eosinophil count and basophil count. In the lowest risk group, the median survival time was 98 months. In the middle group, the median was 65 months, and in the highest risk group, the median was about 42 months. Of all patients analyzed, the longest survival time was 117 months.^[14] However, this study pre-dates the advent of treatments using targeted therapy. A follow-up on patients using imatinib published in the New England Journal of Medicine shows an overall survival rate of 89% after five years.^[15]

Epidemiology

CML occurs in all age groups, but most commonly in the middle-aged and elderly. Its annual incidence is 1–2 per 100,000 people, and slightly more men than women are affected. CML represents about 15–20% of all cases of adult leukemia in Western populations.^[1] The only well-described risk factor for CML is exposure to ionizing radiation; for example, increased rates of CML were seen in people exposed to the atomic bombings of Hiroshima and Nagasaki^[16]

References

1. ^ ^{a b c d} Faderl S, Talpaz M, Estrov Z, Kantarjian HM (1999). "Chronic myelogenous leukemia: biology and therapy". Annals of Internal Medicine 131 (3): 207–219. PMID 10428738. 
2. ^ ^{a b c d e f} Tefferi A (2006). "Classification, diagnosis and management of myeloproliferative disorders in the JAK2V617F era". Hematology Am Soc Hematol Educ Program 2006: 240–245. doi:10.1182/asheducation-2006.1.240. PMID 17124067. 
3. ^ ^{a b c d} Hehlmann R, Hochhaus A, Baccarani M; European LeukemiaNet (2007). "Chronic myeloid leukaemia". Lancet 370 (9584): 342–50. doi:10.1016/S0140-6736(07)61165-9. PMID 17662883. 
4. ^ Savage DG; Szydlo RM; Goldman JM (1997). "Clinical features at diagnosis in 430 patients with chronic myeloid leukaemia seen at a referral centre over a 16-year period". Br J Haematol 96 (1): 111–116. doi:10.1046/j.1365-2141.1997.d01-1982.x. PMID 9012696. 
5. ^ ^{a b c} Tefferi A, Thiele J, Orazi A, Kvasnicka HM, Barbui T, Hanson CA, Barosi G, Verstovsek S, Birgegard G, Mesa R, Reilly JT, Gisslinger H, Vannucchi AM, Cervantes F, Finazzi G, Hoffman R, Gilliland DG, Bloomfield CD, Vardiman JW (2007). "Proposals and rationale for revision of the World Health Organization diagnostic criteria for polycythemia vera, essential thrombocythemia, and primary myelofibrosis: recommendations from an ad hoc international expert pane". Blood 110 (4): 1092–1097. doi:10.1182/blood-2007-04-083501. PMID 17488875. 
6. ^ Nowell PC (2007). "Discovery of the Philadelphia chromosome: a personal perspective". Journal of Clinical Investigation 117 (8): 2033–2035. doi:10.1172/JCI31771. PMID 17671636. 
7. ^ Kantarjian H, Dixon D, Keating M, Talpaz M, Walters R, McCredie K, Freireich E (1988). "Characteristics of accelerated disease in chronic myelogenous leukemia". Cancer 61 (7): 1441–6. doi:10.1002/1097-0142(19880401)61:7<1441::AID-CNCR2820610727>3.0.CO;2-C. PMID 3162181. 
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External links

• Chronic Myeloid Leukemia at American Cancer Society
• CML information from The Leukemia & Lymphoma Society
• Merck Manual:Chronic Myelocytic Leukemia (CML)

v • d • e Myeloid Hematological malignancy/leukemia histology (ICD-O 9590-9989, C81-C96, 200-208) CFU-GM/ and other granulocytes CFU-GM Myelocyte AML: Acute myeloblastic leukemia (M0, M1, M2), APL/M3 MP (Chronic neutrophilic leukemia) Monocyte AML (AMoL/M5, Myeloid dendritic cell leukemia) CML (Philadelphia chromosome, Accelerated phase chronic myelogenous leukemia) Myelomonocyte AML (M4) MD-MP (Juvenile myelomonocytic leukemia, Chronic myelomonocytic leukemia) Other Histiocytosis CFU-Baso AML (Acute basophilic) CFU-Eos AML (Acute eosinophilic) MP (Chronic eosinophilic leukemia/Hypereosinophilic syndrome) MEP CFU-Meg AML (AMKL/M7) MP (Essential thrombocytosis) CFU-E AML (Erythroleukemia/M6) MP (Polycythemia vera) MD (Refractory anemia, Refractory anemia with excess of blasts, Chromosome 5q deletion syndrome, Sideroblastic anemia, Paroxysmal nocturnal hemoglobinuria, Refractory cytopenia with multilineage dysplasia) CFU-Mast Mastocytoma (Mast cell leukemia, Mast cell sarcoma, Systemic mastocytosis) Multiple/unknown AML (Acute panmyelosis with myelofibrosis, Myeloid sarcoma) · MP (Myelofibrosis) · Acute biphenotypic leukaemia myeloid navs: cells/physio, disease of RBCs+megakaryocytes/monocytes+granulocytes/neoplasia, symptoms+signs/eponymous

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