Chronic myeloid leukemia (CML) is a cancer of white blood cells affecting adults and is rarely found in children. In CML, excess growth of immature white blood cells, known as granulocytes, occurs. These immature myeloblasts or granulocytes keep increasing in the bone marrow and subsequently in the blood, which in turn affects the development of other blood cells like red blood cells, white blood cells, and platelets. With advanced treatment, this cancer is now treatable with a good prognosis. People cannot genetically inherit CML from their parents.
Bone marrow and blood
Alternative Name of Chronic Myeloid Leukemia
Chronic granulocytic leukemia
Chronic myelogenous leukemia
Stages of Chronic Myeloid Leukemia
Chronic myelogenous leukemia has three stages.
Chronic phase: It is the initial stage of CML with no or minimal symptoms. Few blast cells (10%) are found in the bone marrow.
Accelerated phase: In this stage, the myeloblast increases to approximately 20% and other feature. The body starts presenting a few symptoms in this stage.
Blastic phase: In this phase, myeloblasts outnumber (more than 20%) the normal functioning RBCs, WBCs, and platelets. The symptoms become severe in this stage, which include enlargement of the spleen, severe infections, bleeding, and extreme weight loss, accompanied by weakness.
Chronic Myeloid Leukemia Causes
Radiation exposure: It is common among atomic bomb survivors or patients exposed to heavy radiation. The patients treated with a high dose of radiation for other cancers can develop CML. Exposure from dental and full-body scans is, however, safe and doesn’t cause CML.
Mutation in the stem cells: The exchange between two different sections of chromosomes (chromosome 9 and 22) in abnormal blood cells gives rise to a new mutated form of chromosome named Philadelphia chromosome, a commonly found gene in CML patients.
Chronic Myeloid Leukemia Symptoms and Signs
During the initial phase, CML doesn’t produce any symptom and may get detected through a routine blood test that shows an increased granulocyte count. In the extreme stage, also known as blast crisis, symptoms start appearing and those include:
A doctor diagnoses CML through different tests like complete blood count, biopsy, imaging after taking a complete medical history, and physical examination.
Complete blood count (CBC): This test can provide the initial picture of CML by showing immature granulocytes in the blood film.
Bone marrow biopsy: This is another test done to diagnose cancers. A needle is inserted into the bone to aspirate marrow and checked for the presence of cancerous cells.
Molecular testing: This test is done later to look for specific genes and proteins that code for the CML, for example, cytogenetic testing.
Typical test to diagnose CML
Fluorescence In situ Hybridization (FISH) is a typical test to diagnose CML as it can identify the BCR-ABL1 gene.
Other tests include Quantitative Polymerase Chain Reaction (qPCR).
Chronic Myeloid Leukemia Treatment
Targeted therapies have revolutionized the treatment of cancers like chronic myeloid leukemia by targeting only the defective part of the gene and sparing other cells. Imatinib, a tyrosine kinase inhibitor, is a type of targeted therapy and is a drug of choice for treating CML. Drugs like imatinib, nilotinib, dasatinib, etc. stop the growth and function of defective genes and eventually cause their death.
Chronic myeloid leukemia is an uncommon cancer type in India and occurs in 0.2 to 2 per 100,000 people in India. It is more common in men and occurs in late adulthood.
Chronic myeloid leukemia has a good prognosis if detected in earlier stages. Targeted therapies and bone marrow transplantation have increased the life span of patients of CML.
The natural progression of CML occurs in phases. Patients usually show no symptoms in this stage. If untreated, patients progress to subsequent phases, accelerated and then blastic phase. The later stages are accompanied by extreme diseased conditions and can be fatal. The median survival of CML decreases with advancing disease. However, diagnosis and treatment in the initial phases can dramatically change the course of this disease with an increase in the survival rate of patients.
Chronic myeloid leukemia is caused by translocation or switching of sections of two different chromosomes that form a new mutated chromosome, named the Philadelphia chromosome (named after the city where it was discovered by two scientists). This mutated chromosome BCR-ABL1 produces defective proteins (tyrosine kinase) that lead to uncontrolled growth of granulocytes in the marrow.