NCCN Guidelines for Patients® | Chronic Myeloid Leukemia

11 NCCN Guidelines for Patients ® : Chronic Myeloid Leukemia, 2018 BCR-ABL1 is a fusion gene. It is not found in normal blood cells. It is not passed down from parents to children. It codes for a protein that causes too many granulocytes to be made. These granulocytes aren’t normal. They don’t mature and don’t die as they should. BCR-ABL1 is formed by a translocation between chromosomes 9 and 22. See Figure 4 . Chromosome 9 has the ABL gene. During the translocation, the ABL gene attaches to chromosome 22. This abnormal chromosome 22 is called the Philadelphia chromosome. The Philadelphia chromosome is the hallmark of CML. It contains the BCR-ABL1 gene. If you do not have the Philadelphia chromosome or the BCR-ABL1 gene, you do not have CML. Three phases There are three phases of CML. They are called chronic, accelerated, and blast phases. They are based on the number of blasts in the blood and marrow. Blasts are early forms of blood cells. They are stem cells that can’t become normal, mature cells. Most cases of CML don’t have high blast counts. High numbers of blasts are a sign of more advanced phases of CML. Chronic phase The first phase of CML is called the chronic phase. In this phase, there is an increased number of white blood cells in the blood, marrow, or both. Less than 10 out of every 100 blood cells are blasts (<10%). Most often, there are no cancer symptoms in the chronic phase. If present, symptoms are often mild. You may have fatigue. You may have a feeling of 1 CML basics Three phases Figure 4 Philadelphia chromosome The Philadelphia chromosome is formed by a translocation between parts of chromosomes 9 and 22. It contains the abnormal BCR-ABL1 fusion gene. Copyright © 2017 National Comprehensive Cancer Network ® (NCCN ® ). Chromosome 9 ABL gene Chromosome 22 BCR gene Normal chromosomes Chromosomes break Changed chromosomes BCR-ABL1 gene Philadelphia chromosome Chromosome 9 Chromosome 22 Chromosome 9 BCR gene ABL gene