Leukemia is a cancer of the blood and bone marrow in which the body produces abnormal white blood cells that don’t function properly. These faulty cells multiply out of control and crowd out the healthy blood cells your body needs, leading to problems with fighting infections, carrying oxygen, and stopping bleeding. About 67.8% of people diagnosed with leukemia survive five years or longer, though that number varies widely depending on the type.
How Leukemia Develops
Your bone marrow constantly produces new blood cells: red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help your blood clot. Leukemia starts when one of the stem cells responsible for making blood cells picks up a genetic mutation that causes it to grow abnormally.
In acute forms of the disease, the mutated cells are immature and barely functional. They’re called blasts, and they replicate rapidly, filling the bone marrow and spilling into the bloodstream. Because the marrow is packed with these useless cells, it can’t produce enough healthy ones. That’s why leukemia doesn’t just cause one symptom; it disrupts multiple systems at once.
In chronic forms, the abnormal cells are partially mature. They look more like normal blood cells under a microscope, but they don’t work well and they divide too quickly. They build up more gradually in the blood and organs like the spleen and lymph nodes, which is why chronic leukemia often progresses more slowly and may go undetected for months or years.
The Four Main Types
Leukemia is classified along two axes: how fast it progresses (acute or chronic) and which type of white blood cell is affected (lymphoid or myeloid). This creates four major categories.
- Acute lymphoblastic leukemia (ALL) affects lymphoid cells and is the most common childhood cancer. It progresses quickly and requires immediate treatment, but cure rates in children are high.
- Acute myeloid leukemia (AML) affects myeloid cells. It occurs most frequently in adults over 60, though it can appear at any age. AML advances rapidly and is typically more difficult to treat than ALL.
- Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. It develops slowly, and some people live for years without needing treatment.
- Chronic myeloid leukemia (CML) also progresses slowly at first and is strongly associated with a specific genetic abnormality called the Philadelphia chromosome.
Symptoms and Why They Happen
Because leukemia disrupts the production of all healthy blood cells, not just white ones, it causes a wide range of symptoms. Each symptom traces back to a specific shortage:
Too few red blood cells means your tissues aren’t getting enough oxygen. That’s what causes the persistent fatigue, weakness, and pallor that many people notice first. Too few platelets makes it hard for blood to clot normally, which leads to easy bruising, frequent nosebleeds, and tiny red dots on the skin called petechiae (small broken blood vessels visible just beneath the surface). Too few functional white blood cells leaves you vulnerable to infections that come on frequently or hit harder than usual.
Other common signs include fever or chills, unexplained weight loss, night sweats, swollen lymph nodes, an enlarged spleen or liver, and bone pain or tenderness. None of these symptoms is unique to leukemia, which is part of what makes early detection challenging. Many people are diagnosed after routine blood work reveals an abnormal white blood cell count.
Known Risk Factors
Most cases of leukemia have no single identifiable cause, but several factors increase risk. Exposure to benzene, a chemical found in gasoline, cigarette smoke, certain adhesives, and industrial solvents, is one of the best-established environmental links. Cigarette smoke alone accounts for roughly half of the total benzene exposure in the U.S. population.
Previous radiation exposure, including from cancer treatment, raises the risk. So does a history of chemotherapy for a different cancer. Certain inherited genetic conditions, including Down syndrome, carry a higher likelihood of developing leukemia. Having a close family member with CLL slightly increases your own risk, though most people with leukemia have no family history of the disease.
How Leukemia Is Diagnosed
Diagnosis typically starts with a complete blood count that shows abnormal numbers of white blood cells, red blood cells, or platelets. If those results look suspicious, a bone marrow biopsy confirms the diagnosis. A pathologist examines the marrow sample under a microscope, looking for the proportion of immature blast cells. For AML, the current diagnostic threshold is 20% or more blast cells in the bone marrow, a standard set by the World Health Organization in 2001 (previously the cutoff was 30%).
Beyond identifying blasts, doctors run genetic and molecular tests on the leukemia cells themselves. These tests reveal specific mutations and chromosomal changes that determine the subtype and guide treatment decisions. This step matters enormously because two people with the same broad type of leukemia can have very different genetic profiles and very different prognoses.
Treatment Options
Treatment depends heavily on the type, the genetic profile, and the patient’s age and overall health. Chemotherapy remains the backbone for most acute leukemias, often given in phases: an initial intensive round to push the disease into remission, followed by additional cycles to keep it there.
Targeted therapies have transformed outcomes for certain subtypes. CML, for instance, is now managed with oral medications that specifically block the protein produced by the Philadelphia chromosome. Before these drugs existed, CML was far more dangerous; today, many patients take a daily pill and live normal lifespans.
Immunotherapy, particularly a technique called CAR T-cell therapy, has been a major advance for cases that don’t respond to standard treatment. In this approach, a patient’s own immune cells are collected, genetically modified in a lab to recognize and attack leukemia cells, then infused back into the body. The FDA approved the first CAR T-cell therapy in 2017 for children with ALL that had relapsed after other treatments. It’s now a standard option for those children and has been expanded as a second-line treatment for some adult blood cancers as well.
Stem cell transplant (also called bone marrow transplant) is another option, particularly for younger patients with aggressive disease. It involves replacing the diseased bone marrow with healthy marrow from a donor after high-dose chemotherapy or radiation wipes out the existing marrow.
Children vs. Adults
Leukemia behaves differently depending on age, and the differences go deeper than just which type is most common. ALL accounts for the majority of childhood leukemia cases, and children with ALL respond exceptionally well to treatment, with cure rates above 90% in many programs. AML in children, while less common, also has better outcomes than adult AML.
A large National Cancer Institute study found that the genetic makeup of AML in children is fundamentally different from AML in adults. Adult AML tends to be driven by point mutations (small changes in individual genes), while childhood AML more often involves large structural rearrangements of chromosomes. This distinction matters because treatments developed and tested primarily in older adults may not work the same way in children. Researchers increasingly recognize that pediatric leukemia needs therapies tailored to its own biology rather than scaled-down versions of adult protocols.
For adults, outcomes vary widely by subtype. CLL and CML often progress slowly enough that people live for decades with the disease, while AML in older adults remains one of the more challenging cancers to treat. Age, genetic risk factors within the leukemia cells, and how quickly the disease responds to initial treatment all shape the long-term outlook.