ATL is a rare cancer that results from long-term infection with the HTLV-1 virus. Most subtypes of this cancer are aggressive and have a poor outlook. But emerging treatments may offer new hope.

Adult T-cell leukemia (ATL) is a rare and aggressive cancer of the immune system. It’s also called adult T-cell leukemia/lymphoma (ATLL).

ATL occurs when a specific virus infects immune system cells called T cells. But it can be decades after infection before cancer develops.

Though the virus affects between 10 and 20 million people worldwide, fewer than 5% of people with an infection will develop ATL later in life.

ATL is difficult to treat and generally has a poor outlook. But new treatments in development have the potential to improve survival rates.

What are T cells?

T cells are a type of white blood cell called lymphocytes. T cells are part of the immune system and protect your body from infections. If a T cell comes across an infected cell while circulating the blood, it will destroy the cell and send out a signal to your immune system.

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ATL results from long-term infection with human T-cell leukemia virus type 1 (HTLV-1), also known as human T-lymphotropic virus-1. People can contract or transmit the virus through:

  • breast milk
  • sexual contact
  • blood transfusions
  • sharing contaminated needles

HTLV-1 is a type of retrovirus. It was the first human retrovirus scientists ever linked to cancer.

Researchers are still trying to understand exactly how the virus causes ATL. Over time, the virus damages the cells’ DNA, which causes them to grow uncontrollably.

People with a longstanding HTLV-1 infection are at the highest risk of ATL. Since the virus stays dormant in the body for decades, people who develop an infection at a young age have a higher risk of having ATL later in life.

Still, only about 4% of people with HTLV-1 end up with a later diagnosis of ATL.

You may be at a higher risk of ATL if you live in one of the following areas where HTLV-1 is endemic (widespread):

  • Japan
  • the Caribbean
  • sub-Saharan Africa
  • the Middle East
  • South and Central America

Japan reports more ATL cases each year than any other country. The virus isn’t common in North America but may be emerging among intravenous (IV) drug users in the United States.

Since the virus can spread through breast milk, babies who drink breast milk may be more likely to contract HTLV-1 than babies who don’t.

Countries that screen blood donations for HTLV-1, such as the United States, have a low risk of spreading the virus through blood transfusions.

There are four subtypes of ATL:

  • Acute: About 55% of ATL cases are acute. Acute ATL is the most aggressive form of ATL.
  • Lymphoma: About 20% of ATL cases are lymphoma. This type also tends to grow aggressively.
  • Chronic: This type accounts for another 20% of ATL cases. Doctors may categorize chronic ATL as either favorable or unfavorable, depending on how the disease affects the body.
  • Smoldering: This is the least common form of ATL (5% of cases) and the least aggressive.

Signs and symptoms of ATL will depend on the type. But in general, you might expect:

Favorable chronic and smoldering ATL usually cause milder symptoms.

About half of people with ATL experience skin lesions. The lesions may appear red, scaly, patchy, flat, or crusted. They usually aren’t itchy.

A doctor will likely ask about your symptoms and medical history. They may take a blood or bone marrow sample or a small piece of affected tissue, such as a swollen lymph node or a skin lesion. They’ll send the sample to a specialist to look for signs of ATL.

Treatment for ATL may depend on the subtype and your overall health.

For acute, lymphoma, and unfavorable chronic ATL, treatment may include:

A stem cell transplant could potentially cure ATL. But this procedure carries serious risks, such as infection, transplant rejection, and even death. Younger people often cope better with a stem cell transplant and have fewer complications than older people.

Researchers are currently studying several new treatments in clinical trials to see if they can improve the outcome for people with ATL. For example, the immunotherapy drug lenalidomide has shown promising results in a phase 2 clinical trial. Researchers are also testing it in another study in combination with chemotherapy.

For smoldering and favorable chronic ATL, which grow more slowly, your doctor may instead monitor the cancer before moving to more aggressive treatment. This is called active surveillance.

The outlook is poor for most subtypes of ATL. In a large retrospective study in Japan, median survival for each subtype was:

ATL subtypeMedian survival (months)

Median survival is the time from either diagnosis or the start of treatment that half of people are still alive.

About half of people with smoldering or favorable chronic ATL eventually progress to acute ATL.

Resources for support

Talk with a doctor about resources available to help with your cancer journey, including any support groups that meet virtually or in person. A social worker or financial counselor may be able to help you navigate the financial aspects of care. A mental health counselor can help you cope with the emotions that may come with a cancer diagnosis.

You can find more support resources from these organizations:

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ATL is a rare cancer due to long-term infection with HTLV-1. Though ATL has a poor outlook, new treatments are emerging that could improve survival rates. If you’ve recently received an ATL diagnosis, ask your doctor about participating in a clinical trial in your area.