Leukemia is cancer that starts in blood-forming cells

Leukemia is a cancer of the blood. It begins when bone marrow—the spongy tissue inside your bones—starts making too many white blood cells that don't work properly. These abnormal cells multiply faster than healthy ones, crowd out normal blood cells, and eventually spread into the bloodstream and other organs. Unlike solid tumors you can see on an X-ray, leukemia is a disease of the blood itself.

The disease develops over time. In most cases, a single cell in the bone marrow develops a genetic change that causes it to divide uncontrollably. This happens by chance—not because of anything you did or didn't do. As these abnormal cells multiply, they interfere with the bone marrow's ability to make healthy red blood cells, white blood cells, and platelets, which leads to the symptoms people experience.

Key Takeaways

  • Leukemia starts in bone marrow when cells begin dividing uncontrollably and crowd out healthy blood cells.
  • There are four main types of leukemia, divided by how fast they develop and which type of white blood cell is affected.
  • Common symptoms include fatigue, frequent infections, easy bruising, and bleeding that doesn't stop quickly.
  • Diagnosis requires a blood test and usually a bone marrow biopsy to confirm the type and plan treatment.
  • Treatment options vary widely depending on the type of leukemia, age, and overall health, and may include chemotherapy, targeted drugs, or stem cell transplant.

The four main types of leukemia

Leukemia is divided into four main categories based on how fast it develops and which type of white blood cell is involved. Acute lymphoblastic leukemia (ALL) develops quickly and affects lymphoid cells, which normally fight infection. Acute myeloid leukemia (AML) also develops quickly but affects myeloid cells, a different type of white blood cell. Both acute forms progress rapidly and require prompt treatment.

Chronic lymphocytic leukemia (CLL) develops slowly and affects lymphoid cells over months or years. Chronic myeloid leukemia (CML) develops slowly and affects myeloid cells. People with chronic leukemia may not have symptoms for a long time and might discover the disease during a routine blood test.

The type matters because it determines how the disease behaves, how fast it spreads, and which treatments work best. A doctor will identify which type you have through blood tests and bone marrow examination before discussing treatment options.

Why symptoms happen and what to watch for

Symptoms occur because abnormal leukemia cells crowd out healthy blood cells. When there aren't enough healthy red blood cells, you feel tired and short of breath. When white blood cells aren't working properly, infections become more frequent and harder to fight. When platelets—cells that help blood clot—are too few, you bruise easily or bleed from small cuts.

Common symptoms include persistent fatigue that doesn't improve with rest, fever that comes and goes, frequent infections like sore throats or pneumonia, easy bruising or bleeding gums, and bleeding that takes longer than normal to stop. Some people also have bone or joint pain, swollen lymph nodes, or a swollen spleen that causes discomfort in the upper left abdomen.

Symptoms vary depending on the type of leukemia and how advanced it is. Acute leukemia symptoms often appear suddenly over days or weeks. Chronic leukemia may cause no symptoms at all in early stages, which is why some people discover it by chance during a blood test for something else.

How leukemia is diagnosed

Diagnosis begins with a blood test that counts different types of blood cells and looks for abnormal ones. If the blood test shows signs of leukemia, the next step is usually a bone marrow biopsy—a procedure where a doctor uses a needle to remove a small sample of bone marrow, usually from the hip bone. This sample is examined under a microscope to confirm leukemia is present and to identify which type.

Additional tests may follow to understand the disease better. These can include flow cytometry (which identifies the exact type of leukemia cell), cytogenetics (which looks for specific genetic changes in the cells), and imaging tests like a chest X-ray or CT scan to see if the disease has spread to other organs.

The results of these tests tell doctors how aggressive the leukemia is, what the likely course will be, and which treatments have the best chance of working. This information guides all treatment decisions going forward.

How leukemia develops differently in children and adults

Leukemia occurs in both children and adults, but the types differ by age group. In children, acute lymphoblastic leukemia (ALL) is the most common type. In adults, acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CLL) are more common. Chronic myeloid leukemia (CML) can occur at any age but is more common in adults.

The prognosis and treatment approach also differ. Children with ALL often have better survival rates than adults with the same disease, partly because their bodies tolerate intensive chemotherapy better. Adults with chronic leukemia may live for years with the disease managed through treatment, while acute leukemia in adults requires immediate, aggressive therapy.

Age affects not only which type of leukemia develops but also how the body responds to treatment and what side effects are most likely. Doctors take age into account when recommending treatment options.

Treatment approaches depend on the type and stage

Treatment for leukemia varies widely based on the specific type, how advanced it is, your age, and your overall health. Chemotherapy uses drugs to kill leukemia cells and is the foundation of treatment for most types. Targeted therapy drugs attack specific genetic changes in leukemia cells and are used for certain types, particularly CML. Immunotherapy helps your immune system recognize and destroy leukemia cells.

For some people, a stem cell transplant (also called a bone marrow transplant) may be recommended. This procedure replaces diseased bone marrow with healthy stem cells from a donor or from your own cells collected and treated beforehand. Transplants are intensive but can offer the best chance of long-term remission for certain types of leukemia.

Some people with chronic leukemia may not need immediate treatment. Doctors monitor these cases closely with regular blood tests and imaging, starting treatment only when the disease begins to progress. This approach, called "watch and wait," avoids the side effects of treatment when the disease is stable.

Living with leukemia and what happens after treatment

During treatment, regular blood tests and bone marrow exams track how well the therapy is working. Remission means leukemia cells are no longer detectable in the blood or bone marrow, though it does not always mean the disease is cured. Some people remain in remission for years or for life. Others may experience a relapse, where leukemia cells return.

After treatment ends, follow-up care continues for years. Doctors monitor blood counts regularly and watch for signs of relapse or side effects from treatment. Some treatments, particularly chemotherapy and stem cell transplants, can cause long-term effects like heart problems, infertility, or secondary cancers, so ongoing screening is important.

Life after leukemia treatment looks different for each person. Some return to normal activities quickly. Others need time to rebuild strength and manage side effects. Support from doctors, nurses, social workers, and support groups helps many people adjust to life after treatment and manage the uncertainty that comes with cancer.

Frequently Asked Questions

Is leukemia hereditary or contagious?

Leukemia is not contagious—you cannot catch it from another person. It is rarely hereditary. Most cases develop because of a genetic change that happens by chance in a single cell, not because of genes inherited from parents. A very small number of families have inherited conditions that increase leukemia risk, but this is uncommon.

What causes leukemia?

The exact cause of most leukemia cases is unknown. Risk factors include age (it is more common in older adults and in children under five), exposure to high-dose radiation, certain chemicals like benzene, smoking, and some genetic conditions. Having a risk factor does not mean you will develop leukemia—many people with risk factors never do.

Can leukemia be cured?

Some types of leukemia can be cured, particularly in children with ALL and some adults with AML who respond well to treatment. Others, like CLL, are often managed as a chronic disease rather than cured. Cure rates depend on the type, age, genetic factors in the leukemia cells, and how well the person responds to treatment. Your doctor can discuss what remission and long-term survival look like for your specific situation.

How long does leukemia treatment take?

Treatment duration varies widely. Intensive chemotherapy for acute leukemia may last several months to a year or more. Chronic leukemia treatment may continue for years or indefinitely. Stem cell transplants involve hospitalization for weeks followed by months of recovery and monitoring. Your doctor will outline the expected timeline based on your type of leukemia and treatment plan.

What should I do if I have symptoms that concern me?

Contact your primary care doctor and describe your symptoms. A blood test can rule out leukemia or identify it early. Early diagnosis does not change the underlying disease, but it allows treatment to begin when it is most likely to work. Do not wait for symptoms to worsen—persistent fatigue, frequent infections, or unexplained bruising warrant a medical evaluation.