CML Overview

What is CML?

CML is a type of cancer that starts in the bone marrow. It results in immature white blood cells growing out of control. This guide covers the chronic phase of CML. This is when most patients are diagnosed.

Chronic persisting for a long time, slow growing
Myeloid relating to bone marrow and to red blood cells, platelets, and certain types of white blood cells
Leukemia a group of cancers that affect blood cells


What causes this disease?

CML comes from a random mutation. It’s not likely that the patient did anything that led to this disease. It is more common as people age, and it’s slightly more common in men than in women. In rare instances, it can come from being exposed to high doses of radiation. Otherwise, no other risk factors are known.

The patient didn’t inherit it from their family through genetics. And it can’t be passed around like a cold, so it didn’t come from anyone else.

It’s simply a random event.

How common is CML?

In the US, there are more than 8,000 new cases of CML diagnosed every year. It accounts for about 15% of all types of leukemia (blood cancers) in adults. It can happen at any age, but the average age at diagnosis is about 64.1

The number of people living with CML has increased over the years. In part, this is due to advances in treatment and monitoring. In the US, it is estimated that there will be at least 140,000 people living with CML by 2030.2

incidence number of new cases identified for a disease
prevalence how many people are living with the disease

How is CML diagnosed?

It’s important to have an annual checkup. This disease is usually suspected based on routine blood work. A few people might experience some symptoms, like fatigue or night sweats. But most don’t.

CML will be confirmed with multiple tests requiring blood and bone marrow samples. A key part of the diagnosis is the presence of the Philadelphia chromosome that everyone with CML has. It’s formed when a patient’s DNA randomly breaks but is put back together improperly. The care team will also need to determine the point at which the DNA broke, sometimes called a “breakpoint”. This guide is written about the subtype that about 99% of CML patients have—hence the name “Major” breakpoint.

Infographic show chromosomes 9 and 22 getting broken and then stuck together to create the Philadelphia chromosome; in addition, show two bowls of different colors and sizes getting broken and then accidentally glued back together, with some indication that it wouldn’t function properly (or other creative means of graphically representing it)

Once CML is confirmed, it’s extremely important to get treatment and monitoring—even if the individual doesn’t feel sick. Excess growth of cancer cells eventually crowds out healthy cells. This can lead to severe sickness and death.3

How is CML treated?

Targeted medications are available. CML is typically treated with a class of medication called tyrosine kinase inhibitor (TKIs).3 The first TKI on the market is called Gleevec® (Novartis), or its generic name imatinib. It was featured on the cover of Time magazine in 2001.4 Since then, additional TKIs have been approved. Each patient will work with their doctor to determine the best option of medication and dosage.



  • %IS: an estimate of the level of leukemia in the blood, lower numbers mean less evidence of leukemia
  • Advanced Phase: a rapidly progressing disease that is Accelerated (rapid uncontrolled growth) and then Blast crisis (difficult to control and dangerous)
  • BCR-ABL1: abnormal genetic molecules created by the Philadelphia chromosome that cause CML, sometimes called a “fusion gene”
  • Bone Marrow: spongy tissue inside some bones (e.g. hip and thigh) that produces many types of blood cells
  • Breakpoints: the exact spot where there is a break in the genes involved in CML
  • Chronic Phase: a long, slow-growing period of CML, often without symptoms, but can progress to Advanced Phase if not treated
  • Chromosome: a long strand of DNA
  • Complete Hematologic Response: CHR, results from blood work have returned to normal, including white blood cells and platelets
  • Complete Molecular Response: CMR, PCR results for BCR-ABL1 are undetectable in a particular test, sensitive tests are better
  • Complete Cytogenetic Response: CCyR, cytogenetic results where the Philadelphia chromosome is undetectable, roughly equivalent to ≤1%IS (≥MR2), 100-fold lower than at diagnosis
  • Cytogenetic Test: a method of examining the structure of the chromosomes, assess the presence or amount of the Philadelphia chromosome
  • Deep Molecular Response: DMR, a sustained period of monitoring where PCR results for BCR-ABL1 are extremely low (<0.01%IS, >MR4), 10,000-fold lower than at diagnosis
  • Early Molecular Response: EMR, PCR results for BCR-ABL1 have reduced to ≤10%IS (≥MR1), 10-fold lower than at diagnosis, at both 3 and 6 months after starting TKI
  • International Scale: IS, a standardized scale for estimating the level of leukemic cells in the blood by measuring BCR-ABL1 (reported as %IS)
  • Leukemia: a group of cancers that affect blood cells
  • Leukemic cells: white blood cells that multiply abnormally; they are immature, meaning that they’re not ready for their normal functions like destroying infectious agents
  • Log reduction: a 10-fold drop in BCR-ABL1 results, such as MR1 to MR2
  • Major Molecular Response: MMR, PCR results for BCR-ABL1 have reduced to ≤0.1%IS (≥MR3) after starting TKI treatment, 1,000-fold lower than at diagnosis
  • Minimal Residual Disease: MRD, general term for the low number of leukemic cells that might persist after treatment
  • Monitoring: a program of testing over time to assess how well CML therapy is working
  • MR value: molecular response, an estimate of the level of leukemia in the blood, higher numbers mean less evidence of leukemia
  • Myeloid: relating to bone marrow and to red blood cells, platelets, and certain types of white blood cells
  • PCR: Polymerase Chain Reaction, a specialized method to estimate the amount of BCR-ABL1 in the blood (also called RT-qPCR or qPCR)
  • Philadelphia Chromosome: a random mistake in the DNA that causes CML, sometimes abbreviated Ph+
  • t(9;22): the translocation also known as the Philadelphia chromosome, resulting from chromosomes 9 and 22 switching sections with each other
  • Treatment-Free Remission: TFR, a lifelong period of monitoring where PCR results for BCR-ABL1 are extremely low or undetectable after discontinuing TKI therapy
  • Tyrosine Kinase Inhibitor: TKI, a class of medications that target the molecules that cause CML
  • Translocation: a type of mistake in DNA where two sections break and then switch with each other
  • White Blood Cell: WBC, also called a leukocyte, cells that circulate the body and help fight infection and disease

CML Overview


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