What Is Leukemia?

In This Article

Leukemia is a group of blood-related cancers that affect white blood cell replication in the bone marrow. The abnormal cells crowd out the healthy cells, which affects their ability to fight infection and impedes the production of blood cells.

There are four major types of the disease. Most of the time, its cause is unknown, but risk factors include genetics, smoking, radiation, and environmental exposures.

Symptoms are non-specific and may include anemia, frequent infections, bruising, and weight loss.

Leukemia may be suspected on blood tests, but further testing is needed to make the diagnosis. Treatment depends on the type and may include chemotherapy, a stem cell transplant, and/or other options.

While acute leukemias are the most common cancer in childhood, in general, leukemia is more common in older adults.

Verywell / Emily Roberts

Types of Leukemia

Leukemia is first classified as acute or chronic and as either myelogenous or lymphocytic.

Acute vs. Chronic Leukemia

Acute leukemias arise from immature cells in the bone marrow (myeloblasts or lymphoblasts). These cells do not function like fully mature ones in fighting off infections. In addition, they often crowd the bone marrow, preventing the production of other blood cells such as red blood cells, other white blood cells, and platelets. Without treatment, acute leukemias often progress very rapidly.

Chronic leukemia arises from mature, but abnormal white blood cells. These cancers grow much more slowly and may be discovered accidentally when a blood count is done for another reason.

Myelogenous vs. Lymphocytic

All of the blood cells derive from pluripotential stem cells in the bone marrow thanks to a process called hematopoiesis. These cells differentiate into either myeloid cells (the myeloid cell line) or lymph cells (the lymphoid cell line). Myeloid cells differentiate into red blood cells, platelets, and the type of cells found in myeloid leukemia: neutrophils, monocytes, and more. Lymphoid cells differentiate into either B lymphocytes (B cells) or T lymphocytes (T cells), and lymphocytic leukemias may begin in either of these cell types.

Leukemia is actually hundreds of different diseases on a molecular level, with no two leukemias being exactly alike.

Acute Lymphocytic Leukemia (ALL)

Acute lymphocytic leukemia, also known as acute lymphoblastic leukemia, is the most common cancer in children. (Combined, acute leukemias are responsible for around a third of childhood cancers.) That said, around 40% of cases occur in adults. While the disease was almost universally fatal a few decades ago, it is now curable in the majority of children diagnosed.

Chronic Lymphocytic Leukemia (CLL)

Chronic lymphocytic leukemia is the most common leukemia in adults and is often diagnosed before any symptoms develop. In some ways, it is very similar to some lymphomas and is treated in a similar fashion.

Acute Myeloid Leukemia (AML)

Although often thought of as childhood cancer, acute myeloid leukemia (acute myelogenous leukemia) is actually more common in adults. In fact, it is the most common form of acute leukemia in these individuals.

The treatment is more aggressive than for other forms of leukemia and often requires in-hospital treatment for the first few weeks. There are several different subtypes of acute myeloid leukemia that differ in many ways, including the prognosis.

One type of AML, acute promyelocytic leukemia, is treated with additional medications specific to the disease. It has the best prognosis of these cancers.

Chronic Myeloid Leukemia (CML)

Chronic myeloid leukemia (CML) is much more common in older adults. CML was the first type of cancer to be successfully controlled with targeted therapies—drugs that zero in on specific abnormalities in the growth of the cells.

These treatments have changed the prognosis from almost universally fatal (eventually) to largely controllable over the long-term with continued treatment.

Both CML and CLL have the potential to become acute leukemia over time.

Leukemia vs Lymphoma

Both leukemias and lymphomas are considered "blood-related cancers" or "liquid cancers," but there are differences. While there are exceptions, some major differences between leukemias and lymphomas include:

  • Location of origin: Leukemias begin in the bone marrow, whereas lymphomas begin in lymph nodes.
  • Symptoms: Lymphomas commonly present with enlarged lymph nodes or constitutional symptoms such as weight loss, night sweats, and fever. Leukemia often presents due to signs of low levels of the blood cells made in the bone marrow, such as pallor, lightheadedness, and fatigue (due to a low red blood cell count), infections (due to improperly functioning white blood cells), and bruising and bleeding (due to a low platelet count).
  • Incidence: Lymphomas are more common than leukemias.
  • Age of onset: Some types of leukemias are more common in children, whereas lymphomas are, by and large, more common in adults.

Leukemia Symptoms

The signs and symptoms of leukemia are often non-specific and may occur with other medical conditions.

Many of these symptoms are related to the decreased number of blood cells (red blood cells, white blood cells, and platelets) produced by the bone marrow or the excess number of white blood cells associated with leukemia.

With acute leukemia, symptoms may come on very rapidly, in a matter of days, whereas with chronic leukemias, symptoms often have a gradual onset over months.

Common symptoms include:

  • Fatigue, weakness, and a general feeling of being unwell
  • Frequent infections
  • Bone and joint pain
  • Unexplained fevers
  • Night sweats
  • Abnormal bruising
  • Bleeding, such as nosebleeds, bleeding when brushing teeth, or heavy periods
  • Enlargement of lymph nodes
  • Enlargement of the spleen or liver


The possible causes and risk factors for leukemia vary between the different forms of the disease.

Radiation exposure is one of the better-studied risk factors and can include radiation related to atomic bombs, nuclear accidents, medical radiation therapy, and even radiation related to diagnostic procedures such as CT scans.

Home and environmental exposures to chemicals such as benzene (found in paints, solvents, gasoline, and more) have also been linked with leukemia.

Smoking is a significant risk factor for AML, and leukemia may be more common in children whose parents smoked during pregnancy.

ALL is more common in children, especially those under age 5 years, while CLL and CML are more common in older adults.

Infection with the human T-cell leukemia virus (HTLV-1) is also a significant risk factor for leukemia, but is uncommon in the United States.

Some medical conditions (such as myelodysplastic syndromes ) as well as previous chemotherapy increase risk.

There are several possible risk factors that are being investigated as well, such as certain dietary practices and radon exposure in the home.

A family history of the disease increases the risk with CLL, but appears to have little role in CML and ALL. Some genetic syndromes, such as Down syndrome and Fanconi anemia elevate risk as well.


The diagnosis of leukemia is often suspected based on the results of a complete blood count (CBC) and peripheral smear, although further tests are usually needed to make the diagnosis.

A bone marrow aspiration and biopsy are helpful in looking for an increased number of blasts in acute leukemia.

Studies on the cells obtained, such as cytochemistry and flow cytometry, can help distinguish AML from ALL, as well as distinguish the subtypes of acute leukemia.

Chromosome and gene studies are very helpful. Cytogenetics (looking at chromosomes in the cancer cells) can find abnormal numbers and characteristics of chromosomes that are common with leukemia.

Further studies such as fluorescent in situ hybridization (FISH) and polymerase chain reaction (PCR) can find other abnormalities in genes and chromosomes that cannot be detected on a cytogenetic analysis alone.

The presence of the Philadelphia chromosome (simplistically, an elongated chromosome 9 and a shortened chromosome 22) is found in over 90% of people with CML.


With acute leukemias (AML and ALL), the mainstay of treatment is usually aggressive induction chemotherapy followed by further chemotherapy, and then maintenance therapy or a bone marrow/peripheral stem cell transplant.

Since chemotherapy does not penetrate well into the brain and spinal cord, preventive treatment (drugs injected directly into the spinal fluid) is often needed with ALL to prevent these cells from persisting and growing.

The treatment of CML has been revolutionized since the advent of targeted medications called tyrosine kinase inhibitors (TKIs), such as Gleevec (imatinib). These medications target a pathway involved in the reproduction of cancer cells and halt the growth of many of these cancers.

The treatment options for leukemia vary with the type of disease.

There are now first-, second-, and third-generation TKIs available, so options exist even if one particular leukemia becomes resistant to one drug. Since targeted therapies control the growth of cancer, but do not kill cancer cells, treatment is often required for the duration of a person's life.

With CLL, treatment is not usually required in the early stages of the disease, and many people can be "treated" with a period of watchful waiting with periodic blood tests. When the disease progresses, treatment with one or more chemotherapy drugs used alone or in combination with a monoclonal antibody or a small molecule (Ibrutinib) is then used.

Since leukemia cells are carried in the bloodstream, and thus throughout the body, local treatments such as surgery or radiation therapy are used infrequently.

Other treatment options are available for leukemias that do not respond to the treatments above, if a person is unable to tolerate treatments, or if the cancer recurs despite treatment.


There are many dimensions to coping with leukemia. Physically, concerns ranging from the need for blood transfusions to the risk of infections may require frequent office visits and careful attention to infection prevention.

Emotionally, leukemia can cause many ups and downs, as is the case with other types of cancer. Leukemia can be even more isolating because of prolonged hospitalizations and infection risk.

Many people survive for years or decades after, or with, leukemia, making attention to the late effects of cancer treatment and other survivorship issues critical.

For young people, concerns over fertility can also arise. Socially, relationships may change or family friction may occur as those around you adjust.

Finally, practical issues ranging from financial concerns to insurance issues can add stress. Fortunately, there are many organizations available that can help people sort through the complex issues that arise during leukemia treatment.


Though it's not always possible to prevent leukemia, there are some ways you may be able to reduce your risk. As with many cancers, eating a diet rich in fruits and vegetables and maintaining a healthy weight may help.

Having an awareness of chemicals at home and on-the-job is also important. While many people think of pesticide exposure as an occupational hazard, home pesticides (such as pet flea collars, home and garden weed killers, and even medications to treat lice) have been implicated in leukemia.

Smoking is thought to be responsible for roughly 20 % of cases of AML. Parental smoking has also been linked with childhood leukemia.

Benzene is a known carcinogen associated with leukemia and can be found in many paints, varnishes, glues, and other home and automotive products.

Recently, attention has also been paid to reducing unnecessary medical radiation associated with diagnostic procedures. While the benefits of these tests often outweigh the risks, it's important to consider other tests or procedures that may not have the same radiation risk and make sure that a test is truly needed.

A Word From Verywell

Leukemia differs from solid tumors in many ways, and those who haven't faced the disease may not recognize many of the challenges. Leukemia is clearly a marathon rather than a sprint, even though treatments may also be more aggressive than with many cancers.

With some leukemias, such as CML, treatment continues throughout life.

Learning as much as you can about the disease and connecting with others through support groups or online communities can be a tremendous help both for getting support from others who understand the special challenges and for staying abreast of the rapidly changing treatment options available.

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Additional Reading
  • Centers for Disease Control and Prevention. Leukemia. Updated 06/12/18. https://www.cdc.gov/cancer/leukemia/index.htm
  • National Cancer Institute. Leukemia – Health Professional Version. https://www.cancer.gov/types/leukemia/hp
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