What Is Leukemia?
A plain-language explanation of leukemia, a group of blood cell cancers, based on National Cancer Institute resources.
Source: National Cancer Institute · Verified 2026-07-02
The 30-second version
Leukemia is a broad term for cancers of the blood cells. The type depends on which blood cell becomes cancer and whether it grows quickly or slowly. It happens most often in adults older than 55, but it is also the most common cancer in children younger than 15.
Key takeaways
- Leukemia is a broad term for cancers of the blood cells.
- The type of leukemia depends on which blood cell becomes cancer and how fast it grows.
- Leukemia occurs most often in adults older than 55.
- It is also the most common cancer in children younger than 15.
- There are several types of leukemia, including acute and chronic forms.
Choose how you want to understand this
The full explanation.
The simple version
Leukemia is a broad term for cancers of the blood cells. Instead of describing a single disease, the word covers a group of related cancers that begin in blood cells.
Leukemia is not one illness — it is a family of blood cell cancers.
What decides the type
The type of leukemia depends on two things:
- The type of blood cell that becomes cancer.
- Whether the cancer grows quickly or slowly.
Because of this, two people can both have "leukemia" and yet have very different types. This is why a healthcare team looks closely at exactly which cells are involved and how fast the cancer is growing.
Who it affects
Leukemia occurs most often in adults older than 55.
At the same time, it is also the most common cancer in children younger than 15. So while it is often thought of as a childhood cancer, it is actually more common in older adults — it simply affects both groups.
Leukemia can happen at many ages, but it is most common in adults older than 55.
The main types
Leukemia has several types. These include:
- Acute lymphoblastic leukemia
- Acute myeloid leukemia
- Chronic lymphocytic leukemia
- Chronic myeloid leukemia
- Hairy cell leukemia
The words "acute" and "chronic" point to how fast the cancer grows. Acute types grow quickly, and chronic types grow slowly. The other words describe the kind of blood cell involved.
Prevention and screening
The National Cancer Institute does not have PDQ evidence-based information about prevention or screening for leukemia. This means there is no standard evidence-based screening test listed for it the way there is for some other cancers. Your healthcare team is the best source for guidance about your own situation.
Watch instead
Animated lessons are in production. Here’s the planned video slate for this topic — each one will be based on the same NCI-sourced explanation you’re reading.
What Is Leukemia: the quick overview
A one-breath explanation you can watch before an appointment.
Coming soonWhat Is Leukemia, explained simply
The core ideas with friendly animation and plain language.
Coming soonUnderstanding what is leukemia — full lesson
A deeper walkthrough covering the key takeaways and common questions.
Coming soonVideo transcript▾
A full, readable transcript will appear here when the video is published — so the lesson is accessible whether you prefer to watch, listen, or read. For now, the article above is the complete text version.
Suggested animation storyboard▾
- 1Open on a calm title card: "What Is Leukemia?" with the Cancer Explained mark.
- 2Narrator reads the 30-second summary while a soft animated diagram builds on screen: "Leukemia is a broad term for cancers of the blood cells. The type depends on which blood cell becomes cancer and whether it grows quickly or slowly. It happens most often in adults older than 55, but it is also the most common cancer in children younger than 15."
- 3Scene 2: illustrate the idea — "Leukemia is a broad term for cancers of the blood cells."
- 4Scene 3: illustrate the idea — "The type of leukemia depends on which blood cell becomes cancer and how fast it grows."
- 5Scene 4: illustrate the idea — "Leukemia occurs most often in adults older than 55."
- 6Close on a reminder card: this is educational only; talk with your healthcare team, and a link to the NCI source.
Words to know
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Quick knowledge check
According to this article, what is leukemia?
Frequently asked questions
▸What is leukemia?
Leukemia is a broad term for cancers of the blood cells. The type depends on which kind of blood cell becomes cancer and whether it grows quickly or slowly.
▸Who gets leukemia?
Leukemia occurs most often in adults older than 55. It is also the most common cancer in children younger than 15.
▸Are there different kinds of leukemia?
Yes. Leukemia has several types, including acute lymphoblastic leukemia, acute myeloid leukemia, chronic lymphocytic leukemia, chronic myeloid leukemia, and hairy cell leukemia.
▸Does the speed of growth matter?
Yes. Part of what defines a type of leukemia is whether it grows quickly (acute) or slowly (chronic).
▸Is there a screening test for leukemia?
The National Cancer Institute does not have PDQ evidence-based information about prevention or screening for leukemia. Your healthcare team can explain more about your situation.
Test your understanding
A few quick questions to check what you took away. Not a test of anything medical — just a way to review.
0 of 4 answered
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Review key terms
Study 8 flashcards built from this topic’s key terms and common questions — flip each card to reveal a plain-language explanation.
Questions to ask your healthcare team
Consider bringing these questions to your next appointment.
- What type of leukemia is being discussed in my case?
- Does this type tend to grow quickly or slowly?
- What do my blood test results mean?
- Where can I find trustworthy information about this type of leukemia?
- Who will be part of my care team?
- What questions should I be asking that I haven't thought of yet?
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