T-cell leukemia is an uncommon form of cancer that causes a type of white blood cells known as T cells to grow uncontrollably in a person’s bone marrow. Adult T-cell leukemia (ATL) is one form of the condition and results from a viral infection.

This information comes from the American Cancer Society.

Experts call the virus that causes ATL human T-cell leukemia virus type-1 (HTLV-1). This virus can also cause a type of lymphoma that begins in the immune system rather than the bone marrow. Doctors refer to the two conditions collectively as adult T-cell leukemia/lymphoma (ATLL).

This article looks at the types, symptoms, and causes of ATL. It also considers the treatment options and survival rates for those with the condition.

Looking over a person's shoulder as they discuss adult T-cell leukemia with a doctor, who sits opposite them. The patient is wearing a blue shirt, while the doctor wears a white coat and stethoscope around their neck. Aside from the blue shirt, the image is in black-and-white.Share on Pinterest
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T-cell leukemia is a relatively rare form of cancer. Like other types of leukemia, it affects blood-forming cells in the bone marrow. These are cells that will go on to become blood cells but that are still in their early, or immature, form.

In addition to plasma, blood consists of red blood cells, white blood cells, and platelets. These cells go through several stages of development before becoming mature.

T-cell leukemia causes an abnormality in a specific type of immature white blood cells, known as T lymphocytes or T cells. T cells protect the body from infection. If these cells become cancerous, they divide and grow uncontrollably.

ATL is a type of T-cell leukemia caused by HTLV-1. The condition is rare in the United States, but it is more common in Japan, parts of Africa, South America, the Middle East, and the Caribbean.

Most people who contract HTLV-1 do not go on to develop any serious disease. HTLV-1 affects around 10 million people globally, but only 2–5% of them develop symptomatic ATLL.

There are four subtypes of ATLL:

  • Smoldering: This type grows slowly and may cause few or no symptoms.
  • Chronic: Chronic ATL also grows slowly. Doctors further categorize chronic ATL into favorable and unfavorable types, depending on the impact the condition is having on a person’s body.
  • Acute: This type grows the fastest and accounts for over 50% of all ATL cases. It is aggressive and the most challenging to treat of all the subtypes.
  • Lymphoma: This subtype begins in the immune system rather than the bone marrow. It can behave in a similar way to acute ATL, growing quickly and aggressively. Another name for this subtype is lymphomatous.

Learn about the differences between leukemia and lymphoma here.

Symptoms of ATL can vary depending on the subtype a person has. People with the smoldering subtype may not have noticeable symptoms or may only develop a few skin lesions.

People with more aggressive forms of ATL may experience:

Hypercalcemia can be serious. It causes symptoms such as:

Children who develop ATLL often experience the acute or lymphomatous subtypes. Many develop an enlarged thymus, an organ that resides in front of the trachea, or windpipe. This can cause breathing problems.

To diagnose ATLL, a doctor will need to take samples of blood, bone marrow, or tissue. This may involve:

A healthcare professional can take blood from a vein in the arm, whereas bone or bone marrow usually comes from a hip bone.

A specialist will then examine the samples for signs of ATLL using various methods. They may use a microscope to examine them closely, or machines that test the sample’s proteins and DNA.

It is possible for ATL to go into remission. This means doctors cannot detect ATL in the body, and a person has no symptoms. Remission can be permanent or temporary.

However, ATL is often aggressive. The acute, lymphoma, and unfavorable chronic subtypes are more difficult to treat, while the favorable chronic and smoldering subtypes have a better prognosis.

For slow-growing forms of ATL, doctors may adopt a “watch and wait” approach to see whether the condition progresses. If the symptoms are mild and do not progress, a person may not need treatment or may not require it for some time.

Around 25% of cases of chronic or smoldering ATLL ultimately progress to the acute form. Anyone with acute ATLL typically undergoes treatment.

First-line treatment for ATL is antiviral therapy. Those with the lymphoma subtype seem to respond better to chemotherapy. Depending on the circumstances, a doctor may recommend one or both approaches.

Some individuals may also receive a stem cell transplantation from a donor, although this combined treatment is still under evaluation for its effectiveness.

Clinical trials are also testing the potential of immunomodulating drugs for ATL treatment.

ATL has a short overall survival rate, even with prompt treatment. This is because ATL is resistant to chemotherapy.

Data from 2000–2009 show that ATL patients who underwent intensive chemotherapy followed by stem cell transplantation had average survival times of:

Average (median) survival timeOverall survival rate after 4 years
Acute8.3 months11%
Lymphomatous10.6 months16%
Chronic31.5 months36%
Smoldering55 months52%

Anyone who has completed treatment for ATLL will receive continuous health monitoring as part of their follow-up care. As the time spent in remission increases, these appointments become less frequent.

ATL occurs due to an infection with HTLV-1, a virus that belongs to the same class of viruses as HIV.

Similarly to HIV, HTLV-1 spreads through contact with bodily fluids. It can transmit through:

There is no cure or vaccine for HTLV-1. There is also no consistent method of screening for HTLV-1 worldwide and no way for doctors to predict who will go on to develop ATL. For this reason, preventing its spread is vital for preventing ATL.

However, because most people with HTLV-1 experience no symptoms, this can be challenging. Few studies have looked at the best ways of preventing HTLV-1 transmission.

Approaches that may help include:

  • Avoiding or limiting breastfeeding: People with newborns may want to reduce the amount of time they breastfeed, or to avoid breastfeeding altogether. Alternatively, people can use the “freeze-thaw” method, which involves expressing the milk, freezing it, and then thawing it before giving it to an infant. This kills the cells that contain HTLV-1. A person should contact a doctor to help them choose the most suitable approach.
  • Screening blood donors: There are ways that health organizations can screen blood donors for HTLV-1 before they give blood. This can reduce transmission via blood transfusions.
  • Barrier methods of birth control: There are no studies confirming that barrier methods of birth control prevent HTLV-1 transmission. As methods such as condoms and dental dams can prevent other sexually transmitted infections from spreading, it is a good idea to use them.

Individuals should seek guidance from a doctor if they have any concerning symptoms, such as new rashes, skin lesions, or persistent fatigue.

They should also contact a doctor if they have come into contact with HTLV-1 at any point.

Where possible, schedule regular doctor visits. These give doctors an opportunity to perform physical examinations and obtain blood tests, as necessary. These may pick up on early signs of illness.

Some people with the slow-growing subtypes of T-cell leukemia have no symptoms. For these individuals, it is essential to visit a doctor as soon as any symptoms appear, because this could be a sign of the disease progressing.

ATL is a type of leukemia that affects the body’s T cells, which play a crucial role in the immune system. An HTLV-1 infection causes ATL.

ATL is often aggressive and difficult to treat. Those with a slow-growing subtype, such as smoldering ATL, usually have a better prognosis. The treatment may involve chemotherapy, antiviral drugs, or stem cell transplantation.