Did the WHO Remove CML's Accelerated Phase in 2022?

Yes. In 2022, the World Health Organization (WHO) updated its 5th-edition classification system for blood cancers and officially removed the “accelerated phase” (AP) for Chronic Myeloid Leukemia (CML) ^{[1] [2]}. Under this specific classification, CML is now described in only two phases: Chronic Phase and Blast Phase ^{[1] [2]}. However, another expert group called the International Consensus Classification (ICC) still recognizes an accelerated phase, so you may hear both terms used by doctors ^{[1] [3]}.

Why Did the WHO Change Its Classification?

Historically, CML was described as having three phases: chronic, accelerated, and blast. This three-phase model was developed before the introduction of tyrosine kinase inhibitors (TKIs), which are oral targeted medicines that have dramatically improved CML survival ^[4]. Because of TKIs, progression to advanced phases has become less common for appropriately treated patients ^[4].

As treatment outcomes improved, researchers found that the traditional criteria for the accelerated phase were highly variable and did not always reliably predict a patient’s prognosis in the modern TKI era ^{[2] [1]}. Instead of relying on a broad intermediate “accelerated” category, the WHO approach encourages doctors to focus on individual high-risk features ^[2]. Today, clinical treatment guidelines emphasize monitoring a patient’s molecular response—measured by a standardized BCR::ABL1 PCR blood test—to ensure the medication is working ^[5].

Warning Signs Still Matter

It is important to understand that the WHO’s removal of the accelerated phase label does not mean the risk of disease progression has disappeared ^[4]. The clinical features that used to define the accelerated phase—such as rising blast counts (10–19%), treatment resistance, or the development of new chromosomal abnormalities—remain critical warning signs ^{[2] [1]}. If a patient develops these features, it often requires a change in medication or more intensive monitoring, regardless of whether the “accelerated” label is formally used.

The Current WHO Phases Explained

Under the 2022 WHO classification, CML is divided into:

• Chronic Phase: The phase in which the vast majority of patients are diagnosed. The disease progresses slowly, and the number of immature white blood cells (blasts) in the blood or bone marrow is typically less than 10% ^[4].
• Blast Phase: An advanced, aggressive phase defined by having 20% or more blasts in the blood or bone marrow, or by an accumulation of blasts outside the bone marrow (extramedullary disease) ^{[4] [1]}. Blast phase can be either myeloid or lymphoid, and it requires highly individualized, intensive treatment that may include a combination of TKIs, acute-leukemia therapies, and consideration for a stem-cell transplant ^{[4] [1]}.

Why You Might Still See the Term “Accelerated Phase”

Even though the 2022 WHO classification omitted it, you might still encounter the term “accelerated phase” in your medical journey:

• Other classification systems: The 2022 International Consensus Classification (ICC) kept a simplified version of the accelerated phase ^{[1] [3]}. Your clinic may use the ICC guidelines instead of the WHO.
• Older records and information: Medical records from before 2022, as well as many online resources and textbooks, still use the three-phase model. Seeing conflicting terms can be confusing, but it does not necessarily mean your disease has suddenly worsened.
• Clinical trials: Some ongoing research studies were designed using the three-phase system and continue to use the term to categorize patients ^[6].

If you see “accelerated phase” in your reports, discuss it with your hematologist to understand which criteria they are using and what specific lab results (like blast percentage or genetic testing) apply to your individual case.