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Understanding leukemia

Classification, risk groups and prognosis

After a diagnosis, doctors work out not only the name of the leukemia but also its exact subtype, its risk group and the prognosis. These three ideas form the basis of the treatment plan. This topic explains how leukemias are classified, why they are not given “stages” the way solid tumors are, how risk groups are built, and what a prognosis means — and what it does not.

Last updated: ~7 min read
A delicate glowing tree on a dark navy background branching from a single shining stem cell; at the tips of the branches are groups of translucent cells in different colours, with a faint DNA helix in the background and a calm mood.
Figure 1.Concept: classification splits the single word “leukemia” into exact types and subtypes.

01Short answer

Classification defines which type and subtype of leukemia someone has. Two main international systems are used today: the 5th edition of the WHO classification (2022) and the International Consensus Classification (ICC, 2022); both combine how the cells look, their surface markers and, above all, their genetic changes. Acute leukemias are not divided into stages I–IV like solid tumors, because the disease is spread throughout the body in the blood and marrow from the start; risk groups are used instead. CLL has Rai and Binet stages, and CML has phases. The risk group (for example, favourable, intermediate or adverse in AML under ELN 2022) is based on genetics, age, blood counts and response to treatment, and it helps decide how intensive treatment should be, including whether a transplant is needed. A prognosis is an estimate based on the experience of a group of similar people, not a personal verdict; it can change and improve during treatment.

02Simple explanation

Classification is the leukemia’s “full name”. “Leukemia” is a general word; doctors are more precise — for example, “AML with an NPM1 mutation” or “B-cell ALL with ETV6::RUNX1”. This exact name matters for choosing treatment.

In many cancers, a tumor is given a stage (I–IV) based on its size and spread. Acute leukemias are different: the leukemia cells are in the blood and marrow from the very beginning. So “stage IV” does not apply to leukemia and does not carry that frightening meaning.

A risk group is a category that helps predict how the disease will respond to treatment. It is based mainly on the genetics of the leukemia cells, age, blood counts and the first results of treatment.

The risk group helps choose the intensity of treatment: in a favourable group, unnecessarily harsh treatment can be avoided; in a high-risk group, stronger treatment, such as a stem cell transplant, can be planned.

A prognosis is an estimate of how the disease is likely to go. It is based on the results of many people like you, but it does not write your personal story in advance. You can tell your doctor how much you want to know about your prognosis, and when.

03Scientific explanation

Classification systems: the 5th edition of the WHO classification (2022) classifies tumors by defining genetic changes wherever possible; for most genetically defined types of AML the 20% blast cut-off has been dropped, while the 20% cut-off is kept at the border between MDS and AML. The ICC (2022) proposes a 10% blast threshold for many genetically defined AMLs and created an “MDS/AML” category for cases with 10–19% blasts. The old FAB system (M0–M7) is no longer used as the main classification. WHO 2022 no longer requires an accelerated phase in CML and instead highlights high-risk features, because in the TKI era the 10-year overall survival in CML is 80–90%.

Risk in acute leukemias: ELN 2022 divides AML in adults into favourable, intermediate and adverse risk groups based on genetic findings (for example, an NPM1 mutation without FLT3-ITD is favourable, a TP53 mutation adverse). In childhood ALL (NCI), the risk group depends on B or T lineage, age and white count (standard risk: age 1 to under 10 and white count <50,000/µL), genetics, CNS involvement and MRD at the end of induction. In APL, risk is defined by the white count at diagnosis (≤10 × 10⁹/L low–intermediate, >10 × 10⁹/L high).

Stages and risk in chronic leukemias: for CLL, the Rai (0–IV) and Binet (A–C) systems take into account enlarged lymph nodes, spleen and liver, as well as anemia and low platelets. The CLL-IPI combines five factors: a TP53 change or del(17p), unmutated IGHV, β2-microglobulin above 3.5 mg/L, clinical stage (Rai I–IV or Binet B–C) and age over 65; the result is a low, intermediate, high or very high risk group. For CML, the ELN 2020 recommendations prefer the ELTS score — based on age, spleen size, blood blasts and platelets — to the Sokal score.

Prognostic factors (NCI): the type of disease and its genetic changes, age and health before the illness, and response to treatment. Response to treatment — especially MRD — can refine the prognosis beyond the estimate made at diagnosis. Risk groups are based on large studies and change as new drugs arrive: for example, Ph-positive ALL and APL, once regarded as having a poor outlook, now have much better results thanks to targeted therapy.

04What happens in the body?

Why does the name matter?

Dozens of subtypes with different treatments and courses hide behind the single word “AML”. An exact classification lets your doctor choose the most suitable proven treatment and lets you look for the right information about your own disease. Classification is often completed once genetic results arrive, so the diagnosis may be refined in the first days.

The risk group: a map for treatment

A risk group is a kind of road map: it shows how intensive treatment should be and at what point a transplant should be discussed. The risk group is not fixed — the response to treatment, especially the MRD result, can refine or change it. This lets doctors adjust the plan in good time.

In front of a translucent human figure on a dark navy background, a path divides into three softly glowing roads in green, gold and blue tones; all of them lead towards the same clear light in the distance.
Figure 2.A risk group is a road map that helps choose how intensive treatment should be.

Prognosis: about a group, not about you

Prognosis figures are based on people treated years ago and may not fully reflect the newer treatments available today. They are averages: some people have an easier path, others a harder one. Talking about prognosis with your doctor can be difficult — writing questions down beforehand and bringing someone close to you can help.

A softly glowing road stretching towards a distant horizon on a dark navy background; blood cells along it grow gradually brighter, with a calm dawn light on the horizon.
Figure 3.A prognosis is an estimate for a group; each person’s path is different and can change over time.

A prognosis can change

A good response to treatment, a lasting remission and no relapse as time goes by all improve the prognosis. Medicine keeps moving too: new targeted drugs and immunotherapies have changed results in many types of leukemia. So the number you hear on the day of diagnosis is not the last word on your journey.

05From diagnosis to prognosis

Four steps — from an exact name to a personal treatment plan.

Exact diagnosis — Microscope, markers and genetics.1Exact diagnosisMicroscope, markers and genetics.
Classification — Type and subtype under WHO 2022 or ICC.2ClassificationType and subtype under WHO 2022 or ICC.
Risk group — Genetics, age, blood counts, overall health.3Risk groupGenetics, age, blood counts, overall health.
Response and reassessment — MRD and remission refine the plan.4Response and reassessmentMRD and remission refine the plan.
The right treatmentIntensity is chosen according to risk.
Realistic expectationsPrognosis is based on group data.
A picture that can changeA good response improves the outlook.

06Classification and risk tools in the main leukemias

LeukemiaHow it is classified / stagedRisk toolWhat matters most for the outlook
AMLWHO 2022 or ICC; genetic subtypesELN 2022: favourable / intermediate / adverseGenetics, age and overall health, MRD
APLA distinct type of AML with PML::RARAWhite count: ≤10 or >10 × 10⁹/LEarly treatment; ATRA + arsenic trioxide
ALLB or T lineage; genetic subtypesStandard / high risk (age, white count, genetics)Genetics and MRD
CMLChronic or blast phaseELTS (or Sokal) scoreMolecular response to TKIs
CLLRai (0–IV) and Binet (A–C) stagesCLL-IPITP53 / del(17p), IGHV status
Hairy cell leukemiaClassic HCL is separated from other B-cell diseasesNo separate widely used scoreUsually a good response to treatment

* This table is a simplified summary; risk systems are updated from time to time and may differ between centres. Your hematologist will explain your risk group and what it means.

07Key terms

Classification
Defining the type and subtype of leukemia according to international rules.
WHO 2022
The 5th edition of the World Health Organization classification of blood and lymphoid tumors.
ICC
International Consensus Classification — a parallel system published in 2022.
Stage
How far a disease has spread; used only in some leukemias (such as CLL).
Risk group
A category patients are placed in according to the expected course of disease.
ELN
European LeukemiaNet — an expert group that writes recommendations for AML and CML.
CLL-IPI
An international prognostic index for CLL based on five factors.
ELTS score
A score that estimates risk in people with CML treated with TKIs.
Prognosis
An estimate of the likely course of a disease.
Prognostic factor
A feature that affects the prognosis, such as a genetic change or age.

08Key points

  • Classification gives the leukemia its exact “full name”.
  • The main systems are WHO 2022 and ICC 2022; both give genetics great weight.
  • Acute leukemias are not divided into stages I–IV.
  • CLL uses Rai and Binet stages; CML uses phases.
  • The risk group helps choose how intensive treatment should be.
  • Response to treatment, especially MRD, refines the risk group.
  • A prognosis is an estimate for a group, not a personal verdict.
  • A prognosis can improve over time and with new treatments.

09Frequently asked questions

What stage is my leukemia?

In acute leukemias (AML, ALL), stages are not used; the subtype and risk group are defined instead. CLL has a Rai or Binet stage, and CML has a phase (chronic or blast). Ask your hematologist which system applies to your disease.

I am in the “high-risk” group. Does that mean I will not be cured?

No. High risk means the disease needs stronger treatment, so doctors strengthen the plan — for example, they may offer a transplant or a clinical trial. Many people in high-risk groups also reach long-lasting remission.

Can my risk group change?

Yes. Once genetic results arrive or the response to treatment has been assessed, the risk group may be refined. For example, MRD that clears quickly is a good sign, while persistent residual disease may lead to a change of plan.

I do not want to know my prognosis. Is that normal?

Completely normal. The NCI notes that seeking information about prognosis is a personal decision. You can tell your doctor how much you want to know; some people prefer this information to be shared only with their loved ones.

Do the numbers I found online apply to me?

Not entirely. They are averages for large groups, often of people treated years ago, and they do not take into account your genetics, age or response to treatment. It is better to interpret the numbers together with your hematologist.

Why won’t my doctor give me an exact prognosis?

Because no one can know an individual person’s future for certain. Doctors talk about probabilities and can give more precise information as treatment goes on. That is not vagueness — it is honesty.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. What is my risk group, and what is it based on?

  2. Could my risk group change during treatment?

  3. Can you explain my prognosis in a way I can understand?

  4. Is there anything I can do myself to improve my outlook?

My questions

12Sources

  1. National Cancer Institute (NCI). Understanding Cancer Prognosis
  2. American Cancer Society. How Is Acute Myeloid Leukemia Classified?
  3. American Cancer Society. Typing of Acute Lymphocytic Leukemia (ALL)
  4. American Cancer Society. Chronic Lymphocytic Leukemia Stages
  5. American Cancer Society. Phases of Chronic Myeloid Leukemia
  6. Leukemia (Nature) — WHO 5th edition. The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic Neoplasms
  7. Leukemia (Nature) — WHO 5th edition. The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Lymphoid Neoplasms
  8. Blood (American Society of Hematology), 2022. International Consensus Classification of Myeloid Neoplasms and Acute Leukemias: integrating morphologic, clinical, and genomic data
  9. Blood (American Society of Hematology), 2022. Diagnosis and management of AML in adults: 2022 recommendations from an international expert panel on behalf of the ELN
  10. Leukemia (Nature), 2020. European LeukemiaNet 2020 recommendations for treating chronic myeloid leukemia
  11. The Lancet Oncology, 2016. An international prognostic index for patients with chronic lymphocytic leukaemia (CLL-IPI): a meta-analysis of individual patient data
  12. National Cancer Institute (NCI). Childhood Acute Lymphoblastic Leukemia Treatment (PDQ®) — Health Professional Version
  13. National Cancer Institute (NCI). Chronic Lymphocytic Leukemia Treatment (PDQ®) — Health Professional Version
  14. National Cancer Institute (NCI). Adult Acute Myeloid Leukemia Treatment (PDQ®) — Patient Version
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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