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Understanding the Disease

Philadelphia chromosome–positive chronic myeloid leukemia (Ph+ CML)

What is Ph+ CML?

Philadelphia chromosome–positive chronic myeloid leukemia (Ph+ CML) is a type of cancer affecting the blood and bone marrow. In people with Ph+ CML, the bone marrow produces too many white blood cells, and these cells are often immature or damaged.


In Ph+ CML, your bone marrow cells have an abnormal chromosome that causes your body to produce too many white blood cells. These abnormal white blood cells crowd out normal healthy cells.

What Causes Ph+ CML?

Ph+ CML is caused when genetic material from one chromosome switches position with genetic material from another chromosome. This series of images shows the creation of the Philadelphia chromosome and the BCR-ABL1 gene, the genetic culprits in Ph+ CML.

Chromosomes 9 and 22

We have 46 chromosomes that are found within most of our cells. Within these chromosomes is DNA which codes for our genes. Genes contain instructions for making proteins that are used throughout the body. Damaged genes may create faulty proteins, which may cause harm.1

This image shows normal chromosomes 9 and 22. Within these chromosomes are the normal genes, ABL1 on chromosome 9, and BCR on chromosome 22.


Chromosomes 9 and 22

The Switch

In Ph+ CML, pieces of chromosomes 9 and 22 have broken off and switched places.1


The SwitchThe Switch

Creation of the Philadelphia Chromosome

This creates a new abnormal chromosome called the Philadelphia chromosome, often abbreviated as Ph.


The Philadelphia chromosome contains the abnormal gene, BCR-ABL1, which is the genetic culprit in Ph+ CML.


Creation of the Philadelphia Chromosome

Genes create proteins

In Ph+ CML, the faulty BCR-ABL1 gene creates a faulty protein which is also called BCR-ABL1.1,2


If the faulty BCR-ABL1 protein were healthy, it would send a signal to the bone marrow to turn on and off the production of white blood cells as needed.1,2


But in Ph+ CML, the faulty BCR-ABL1 protein only signals to the bone marrow to be turned on, creating too many white blood cells.1,2 These immature white blood cells, called blasts, are often damaged and can crowd out healthy blood cells.3 This could lead to anemia, fatigue, organ failure, and ultimately, death.2


Genes create proteins


Hear a story from a real patient with Ph+ CML

Robert is a real patient taking TASIGNA® (nilotinib) capsules for Ph+ CML and was compensated by Novartis for his participation in the Ph+ CML Stories Series.

The National Comprehensive Cancer Network makes no warranties of any kind whatsoever regarding their content, use or application and disclaims any responsibility for their application or use in any way.


  1. Druker BJ. Translation of the Philadelphia chromosome into therapy for CML. Blood. 2008;112:4808-4817.
  2. Referenced with permission from the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) for Chronic Myeloid Leukemia V.4.2018. © 2018 National Comprehensive Cancer Network, Inc. All rights reserved. The NCCN Guidelines® and illustrations herein may not be reproduced in any form for any purpose without the express written permission of NCCN. To view the most recent and complete version of the NCCN Guidelines, go online to
  3. National Cancer Institute at the National Institutes of Health. NCI dictionary of cancer terms: blast. Bethesda, MD: U.S. Department of Health and Human Services. Available at: Accessed March 20, 2013