Overview

Definition

Chronic myeloid leukemia is a chronic myeloproliferative neoplasm characterized by uncontrolled and dysregulated proliferation of the granulocytic lineage (mature and maturing cells), with a maintained capacity for differentiation. Chronic myeloid leukemia is also known as chronic myelocytic leukemia or chronic myelogenous leukemia.

Epidemiology

• 20% of all leukemia in adults
• Incidence:
  • In the United States: 1–2 cases per 100,000 inhabitants 
  • Increases with age
• Median age at presentation: approximately 55 years
• Slight male predominance
• No known familial predisposition 
• Prevalence of CML is increasing in developed countries due to the effect of ABL1 kinase inhibitors.

Etiology

• Not known in most cases
• High-dose ionizing radiation is an important risk factor.

Pathophysiology

Hematopoiesis

Hematopoiesis starts with a hematopoietic stem cell, which is prompted to divide and differentiate with appropriate chemical stimuli (hemopoietic growth factors).

• Lymphoid stem cells give rise to lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes.
• Myeloid stem cells eventually differentiate into platelets Platelets Platelets are small cell fragments involved in hemostasis. Thrombopoiesis takes place primarily in the bone marrow through a series of cell differentiation and is influenced by several cytokines. Platelets are formed after fragmentation of the megakaryocyte cytoplasm. Platelets, erythrocytes Erythrocytes Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes, granulocytes (neutrophils, basophils, eosinophils), and monocytes:
  • IL-3 stimulates the differentiation of multipotent hematopoietic stem cells into myeloid progenitor cells.
  • Granulocyte macrophage colony-stimulating factor (GM-CSF) → differentiation from myeloid progenitors to granulocytes (neutrophils) and monocytes 
  • IL-5 → differentiation to eosinophils
  • Thrombopoietin (TPO) → differentiation to thrombocytes ( platelets Platelets Platelets are small cell fragments involved in hemostasis. Thrombopoiesis takes place primarily in the bone marrow through a series of cell differentiation and is influenced by several cytokines. Platelets are formed after fragmentation of the megakaryocyte cytoplasm. Platelets)
  • EPO → differentiation to erythrocytes Erythrocytes Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes (RBCs)

Mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations

Chronic myeloid leukemia is an acquired abnormality of the hematopoietic stem cells in the bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow.

• Mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations occurs in the BCR-ABL1 fusion gene:
  • Involves BCR on chromosome 22 and ABL1 on chromosome 9
  • Typically results from a reciprocal (9;22)(q34;q11) translocation giving rise to the Philadelphia (Ph) chromosome:
    • Abnormal chromosome 22
    • Hallmark genetic aberration of CML
  • BCR-ABL1 fusion gene produces a unique product, the BCR-ABL1 fusion protein.
• BCR-ABL1 protein:
  • Oncogenic protein that induces a persistently enhanced tyrosine kinase activity
  • Deregulated tyrosine kinase activity leads to CML through:
    • Overproliferation of myeloid cells in the bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow
    • Discordant maturation of cells
    • ↓ Apoptosis 
• The clinical hallmark of CML is the uncontrolled production of mature and immature granulocytes:
  • Predominantly neutrophils
  • Some basophils and eosinophils
• ↑ Division of cells → ↑ expansion of the bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow 

Clinical Presentation

General clinical features

• From anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and increased cell turnover:
  • Fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, night sweats
  • Malaise, fatigue
  • Weight loss
• From splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly and splenic infarction:
  • LUQ pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain or fullness
  • Early satiety
• From platelet dysfunction: 
  • Petechiae
  • Ecchymosis
  • Bleeding
• From expanding bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow: 
  • Sternal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain/tenderness
  • Bone pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
• From ↑ uric acid production (uric acid released as a result of cell degradation): gouty arthritis
• From hyperviscosity-related or thrombotic events (due to severe leukocytosis and/or thrombocytosis):
  • Confusion
  • Headache
  • Blurred vision
  • Priapism

Phases of disease

The symptoms discussed above vary in severity depending on the 3 disease phases of CML (based on the immature WBCs or blast cells in the blood or bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow).

Chronic stable phase:

• Blast cells: < 10%
• Most patients present in the chronic stable phase.
• Insidious onset with generally mild symptoms:
  • Up to 50% of patients are asymptomatic (diagnosis based on laboratory tests).
  • Fatigue, malaise
  • Weight loss, sweating
  • Abdominal fullness
• Indolent clinical course with a duration of several years
• Response to therapy is excellent.

Accelerated phase:

• Untreated CML usually progresses to the accelerated phase.
• ≥ 1 of the following features:
  • Blast cells: increase to 10%–19%.
  • Peripheral blood basophils: > 20%
  • Platelet count: < 100,000/µL, not due to therapy
  • Platelets: > 1 million/µL, unresponsive to therapy
  • Progressive splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly and increasing WBC, resistant to therapy
  • New chromosome changes (evolution of leukemic cells seen as chromosomal abnormalities in addition to the Philadelphia chromosome)
• Cells multiply aggressively and cause:
  • Fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever
  • Significant weight loss
  • Severe fatigue
  • Significant bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones and joint pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
  • Abdominal fullness/ pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
  • Bleeding
  • Thrombotic or hyperviscosity symptoms
• Response to therapy is less favorable.

Blast crisis (or acute phase):

• Myeloid or lymphoid blasts proliferate in an uncontrolled manner.
• Presence of ≥ 1 of the following:
  • > 20% of peripheral blood or bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow blasts
  • Large clusters of blasts on bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow biopsy
  • Extramedullary blast proliferation (other tissues/organs beyond the marrow)
• Indistinguishable from acute leukemia: fever, bleeding, petechiae, ecchymosis, pallor, and progressive splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly
• Response to therapy is poor.

Management

Treatment goals and options

• Goals of therapy:
  • Hematologic remission: achieving normal blood counts and spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen size
  • Cytogenetic remission: no Philadelphia chromosome–positive cells
  • Molecular remission: negative BCR-ABL1 fusion gene on PCR
• Treatment is based on the specific disease phase, and options include:
  • Tyrosine kinase inhibitors (TKIs):
    • Inhibit the constitutively active tyrosine kinase and cause apoptosis of neoplastic cells
    • Preferred initial treatment
    • Imatinib, dasatinib, nilotinib, bosutinib, ponatinib
    • Adverse effects: nausea, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, fluid retention, myelosuppression, QT prolongation
  • Allogeneic hematopoietic cell transplantation (HCT)
  • Other agents (used if refractory to initial treatment and/or patient is not a transplant candidate):
    • Hydroxyurea: to reduce WBC
    • Interferon alfa (with/without cytarabine)
    • Busulfan
    • Omacetaxine mepesuccinate (inhibitor of protein synthesis)

Treatment approach

Chronic stable phase:

• TKIs:
  • Treatment of choice for almost all newly diagnosed patients
  • To achieve long-term control in the majority of patients, with cytogenetic and molecular responses
• The prognosis is good.

Accelerated phase:

• Tends to be difficult to control
• TKIs:
  • An initial response may be seen but is generally short-lived.
  • Significant relapse rate even after successful treatment with TKIs
• Allogeneic HCT: 
  • Potentially curative
  • Referral for transplantation (with search for a donor) is also initiated during TKI treatment for all eligible patients.
• The prognosis is poor.

Blast crisis:

• Aggressive disease
• All therapies discussed thus far are viable options.
• Manage as acute leukemia.
• Palliative treatment to relieve symptoms
• The prognosis is dismal.

Monitoring and supportive management

• Monitor the following:
  • CBC to determine hematologic response
  • Chromosome banding analysis (percentage of Philadelphia chromosome–positive cell) to determine cytogenetic response
  • BCR-ABL1 by quantitative PCR to determine the molecular response
• Follow-up of response is critical in predicting when therapies other than TKIs should be considered.
• Supportive therapies:
  • Blood transfusions for anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview
  • Platelet transfusions for thrombocytopenia Thrombocytopenia Thrombocytopenia occurs when the platelet count is < 150,000 per microliter. The normal range for platelets is usually 150,000-450,000/µL of whole blood. Thrombocytopenia can be a result of decreased production, increased destruction, or splenic sequestration of platelets. Patients are often asymptomatic until platelet counts are < 50,000/µL. Thrombocytopenia
• Tumor lysis syndrome Tumor lysis syndrome Tumor lysis syndrome is a potentially lethal group of metabolic disturbances that occurs when large numbers of cancer cells are killed rapidly. The lysed cells release their intracellular contents into the bloodstream, resulting in the development of hyperkalemia, hyperuricemia, hyperphosphatemia, hypocalcemia, and acute kidney injury. Tumor Lysis Syndrome:
  • Medical emergency caused by metabolic disturbances that occurs when large numbers of cancer cells are killed rapidly
  • Lysis of tumor cells leads to the release of intracellular contents into the bloodstream:
    • Electrolyte imbalances (↑ potassium, ↑ phosphate, ↓ calcium) → neurologic, cardiac, and GI complications
    • Increase in nucleic acid breakdown → hyperuricemia, which can lead to AKI AKI Acute kidney injury refers to sudden and often reversible loss of renal function, which develops over days or weeks. Azotemia refers to elevated levels of nitrogen-containing substances in the blood that accompany AKI, which include BUN and creatinine. Acute Kidney Injury
  • Management:
    • Hydration
    • Allopurinol
    • Rasburicase

Differential Diagnosis

Other chronic myeloproliferative neoplasms

• Primary myelofibrosis Primary myelofibrosis Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by chronic myeloproliferation with nonclonal fibroblastic deposition, resulting in bone marrow fibrosis. The abnormality stems from genetic mutations of the hematopoietic stem cells (typically, JAK2 mutation). Primary symptoms are anemia and extramedullary hematopoiesis,. Primary Myelofibrosis: chronic myeloproliferative neoplasm characterized by fibrosis of the bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow and extramedullary hematopoiesis in the spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen and liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Primary myelofibrosis Primary myelofibrosis Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by chronic myeloproliferation with nonclonal fibroblastic deposition, resulting in bone marrow fibrosis. The abnormality stems from genetic mutations of the hematopoietic stem cells (typically, JAK2 mutation). Primary symptoms are anemia and extramedullary hematopoiesis,. Primary Myelofibrosis is linked to mutations in JAK2, CALR, and MPL. There is no BCR-ABL1 fusion gene. Clinical findings are severe fatigue, splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly, hepatomegaly, and anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview. The peripheral blood smear is leukoerythroblastic and contains precursors of WBCs and RBCs, nucleated RBCs, and teardrop cells. Diagnosis is made by bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow examination and molecular testing. Management includes allogeneic HCT and therapy with ruxolitinib and fedratinib.
• Polycythemia vera Polycythemia vera Polycythemia vera (PV) is a chronic myeloproliferative neoplasm characterized by the overproduction of RBCs. In addition, the WBC and platelet counts are also increased, which differentiate PV from erythrocytosis seen with chronic hypoxia and other chronic conditions. Polycythemia Vera: unregulated overproduction of hematopoietic stem cells, mainly RBCs, despite low levels of EPO: In polycythemia vera, there is a gain-of-function mutation in the JAK2 gene. The majority of the patients present with hyperviscosity symptoms. Management includes phlebotomy, low-dose aspirin, and myelosuppressive therapies.
• Essential thrombocythemia Essential thrombocythemia Essential thrombocythemia (ET) is a type of myeloproliferative neoplasm characterized by the clonal thrombocytosis linked to somatic mutations involving Janus kinase 2 (JAK2), calreticulin (CALR), and myeloproliferative leukemia virus oncogene (MPL). Patients can be asymptomatic or present with vasomotor symptoms. Essential Thrombocythemia: proliferation of megakaryocytes, usually due to JAK2, CALR, and MPL mutations, that results in thrombocytosis: The clinical manifestations of essential thrombocythemia are headaches, visual disturbances, and erythromelalgia. Excessive platelet counts result in both thrombosis and bleeding. Management is aimed at reducing the platelet count (with hydroxyurea) and decreasing the risk of thrombosis (by systemic anticoagulation and/or antiplatelet agents Antiplatelet agents Antiplatelet agents are medications that inhibit platelet aggregation, a critical step in the formation of the initial platelet plug. Abnormal, or inappropriate, platelet aggregation is a key step in the pathophysiology of arterial ischemic events. The primary categories of antiplatelet agents include aspirin, ADP inhibitors, phosphodiesterase/adenosine uptake inhibitors, and glycoprotein IIb/IIIa inhibitors. Antiplatelet Agents).
• CNL: rare disorder characterized by the proliferation of mature granulocytes in the blood and marrow: Organ infiltration can occur in CNL, leading to hepatosplenomegaly. There is no Philadelphia chromosome, but an increased LAP score is noted in CNL. Chronic neutrophilic leukemia does not usually progress to AML AML Acute myeloid leukemia (AML) is a hematologic malignancy characterized by the uncontrolled proliferation of myeloid precursor cells. Seen predominantly in older adults, AML includes an accumulation of myeloblasts and a replacement of normal marrow by malignant cells, which leads to impaired hematopoiesis. Acute Myeloid Leukemia. Management options are not well defined, but the JAK1/2 inhibitor, ruxolitinib, is an option.
• CEL CEL Chronic eosinophilic leukemia (CEL) is a chronic myeloproliferative neoplasm caused by autonomous clonal proliferation of normal-appearing eosinophils, resulting in increased eosinophils in the peripheral blood and bone marrow. The disorder is a myeloid variant of hypereosinophilic syndrome (HES) and is associated with tissue infiltration leading to end-organ damage. Chronic Eosinophilic Leukemia, not otherwise specified: rare clonal chronic myeloproliferative disorder characterized by excessive production of eosinophils in the bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow leading to proliferation in the blood and organ infiltration (hepatomegaly/ splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly): According to cytogenetics in CEL CEL Chronic eosinophilic leukemia (CEL) is a chronic myeloproliferative neoplasm caused by autonomous clonal proliferation of normal-appearing eosinophils, resulting in increased eosinophils in the peripheral blood and bone marrow. The disorder is a myeloid variant of hypereosinophilic syndrome (HES) and is associated with tissue infiltration leading to end-organ damage. Chronic Eosinophilic Leukemia, CEL CEL Chronic eosinophilic leukemia (CEL) is a chronic myeloproliferative neoplasm caused by autonomous clonal proliferation of normal-appearing eosinophils, resulting in increased eosinophils in the peripheral blood and bone marrow. The disorder is a myeloid variant of hypereosinophilic syndrome (HES) and is associated with tissue infiltration leading to end-organ damage. Chronic Eosinophilic Leukemia does not exhibit the Philadelphia chromosome or the BCR-ABL1 fusion gene. Management is supportive and involves imatinib therapy.

Other disorders that resemble CML

• Leukemoid reaction: condition characterized by WBC > 50,000/µL from causes other than leukemia: Neutrophilia and prominent left shift, usually in response to infection, are typical. Findings include toxic granulation in the neutrophils, a high LAP score, lack of a myelocyte bulge, and most importantly, the presence of an obvious cause for neutrophilia. Cytogenetic or molecular testing is performed to rule out CML if the distinction cannot be made. Management is supportive and involves treatment of the underlying etiology. Leukapheresis is indicated in the case of hyperviscosity.
• Chronic myelomonocytic leukemia (CMML): rare myelodysplastic/myeloproliferative neoplasm with increased production of maturing monocytic cells and, sometimes, dysplastic neutrophils. Chronic myelomonocytic leukemia is often accompanied by constitutional symptoms, splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly, anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview, and/or thrombocytopenia Thrombocytopenia Thrombocytopenia occurs when the platelet count is < 150,000 per microliter. The normal range for platelets is usually 150,000-450,000/µL of whole blood. Thrombocytopenia can be a result of decreased production, increased destruction, or splenic sequestration of platelets. Patients are often asymptomatic until platelet counts are < 50,000/µL. Thrombocytopenia. Bone marrow morphology shows prominent dysplasia in at least 2 of the 3 myeloid lineages. There is no Philadelphia chromosome or BCR-ABL1 gene. Management includes supportive care, hydroxyurea, a hypomethylating agent, and allogeneic HCT.