T-cell leukemia is an uncommon type of blood cell cancer that affects your white blood cells.

T cells are a type of white blood cell. The purpose of these blood cells is to help your body detect and fight off infection or illness.

These blood cells form and begin to develop in your bone marrow. Immature T cells leave your bone marrow and become mature T cells in your thymus gland, a small organ located behind your breast bone.

Damaged DNA in a T cell can cause uncontrolled cell growth and division. This overproduction of cells is how T-cell leukemia starts.

This article will help explain what T cell leukemia is, the typical symptoms, and how this condition is most often diagnosed and treated.

Leukemia is cancer of your blood cells and the tissues that make these blood cells.

There are many different kinds of leukemia. They’re classified according to whether they’re fast growing (acute) or slow growing (chronic) and by the type of blood cell involved. Most often leukemia involves white blood cells.

There are two kinds of white blood cells. Let’s look at each type in more detail.

Lymphoid cells

These white blood cells are known as lymphocytes, which are the main cells that make up lymph tissue, a major part of your immune system. They help your body fight infection. There are two main types of lymphocytes:

  • T cells. These cells circulate in your blood looking for infected or foreign cells. When they find one, they destroy the cell and send a signal that activates your immune system.
  • B cells. These cells produce antibodies to stop foreign invaders, like viruses or bacteria, from harming your body.
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Myeloid cells

When blood stem cells develop into new blood cells, they can either become lymphocytes or myeloid cells.

Myeloid cells can develop into white blood cells (other than lymphocytes), red blood cells, or platelets. The following types of white blood cells are all examples of mature myeloid cells:

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The four main types of leukemias that can develop include:

Blood cells are made in your bone marrow. Primitive stem cells form there and develop into immature precursor cells. Some of these stay in your bone marrow and become mature B cells. Other precursor cells leave your bone marrow and travel to your thymus where they become mature T cells.

Lymphocytic leukemia develops when the DNA in precursor cells change (mutate) or become damaged. Instead of maturing, the damaged DNA tells these cells to multiply uncontrollably. The result is a large number of abnormal copies of the cell in your bone marrow and bloodstream.

Lymphoma develops when this process occurs in a lymph node or other lymphatic tissue. Most lymphocytic leukemias involve B cells, but there are a few T-cell leukemias.

T-cell prolymphocytic leukemia (T-PLL) is a good example of cancer that affects your T cells, and it’s been studied more than other types.

In the rest of this article, we’ll focus on T-PLL when describing T-cell leukemia.

The most common symptom of T-PLL is an extremely high white blood cell count (lymphocytosis) of about 100,000 cells/microliter (mL) or more. The normal range is 4,000 to 11,000/mL.

Up to 30 percent of people with T-PLL have a high white blood cell count but no other symptoms. In this instance, T-PLL is stable or only progresses slowly. This is called inactive T-PLL.

Eventually, though, the disease becomes active and causes symptoms. This usually happens within 2 years of developing a high white blood cell count.

When symptoms are present, they might include:

  • a rash or other skin lesion caused by white blood cells moving into your skin tissue
  • fluid buildup in your abdominal cavity (ascites) or around your lungs (pleural effusion)
  • swelling and edema in your legs, the skin around your eyes, or the membrane covering your eye (conjunctiva)

Symptoms commonly associated with most other types of leukemia and lymphoma are uncommon in the early stages of T-PLL. But symptoms may appear as the illness progresses. So-called B-cell symptoms can develop, which include:

Sometimes, your bone marrow becomes overcrowded with the large number of T cells, so fewer red blood cells and platelets can be produced. This may cause:

There are also certain symptoms that may indicate white blood cells have infiltrated your organs. Your doctor may notice these during a physical exam and can include:

There aren’t many known risk factors for T-PLL. The average age of diagnosis is about 65, and men are diagnosed with the condition slightly more often than women. It hasn’t been found in children or young adults, except as described below.

You’re more likely to get T-PLL if you have ataxia telangiectasia. This is a rare inherited condition that begins in childhood and affects your immune and nervous systems.

The characteristic symptom is a progressive loss of the ability to coordinate movements (ataxia). As it worsens, activities like walking and balancing become more difficult.

People with ataxia telangiectasia are younger when they develop T-PLL. It usually begins at age 30 or younger.

Your doctor will first do a thorough physical exam. If they suspect some type of condition related to your blood, they’ll order your blood to be tested.

These tests will analyze your white blood cell count and also look for markers and other characteristics of your lymphocytes. Typical tests include:

  • a complete blood count with differential to determine the numbers of each kind of blood cell
  • a peripheral blood smear to evaluate the blood cells under a microscope
  • a flow cytometry to evaluate lymphocyte size, shape, surface markers, and other characteristics
  • an analysis of lymphocyte T-cell receptor arrangements
  • karyotyping to examine your chromosomes
  • fluorescence in situ hybridization (FISH) to look for genetic abnormalities

The information that’s gathered from these tests will help determine whether you meet the criteria for a diagnosis of T-PLL.

Additionally, testing for human T-lymphotropic virus (HTLV) type 1 is usually done. If it’s positive, it means you have adult T-cell leukemia/lymphoma, which is caused by the virus and not T-PLL.

A CT scan of your abdomen, pelvis, and chest will usually be done prior to treatment to evaluate your major organs, such as your liver, spleen, and lymph nodes.

Red blood cells or platelets are usually also evaluated with a bone marrow biopsy before treatment begins.

If you’re asymptomatic, you’ll be followed closely with monthly physical exams and white blood cell counts until your T-PLL becomes active.

Since there’s no benefit until it becomes active, asymptomatic, inactive T-PLL isn’t treated.

Active T-PLL is treated with chemotherapy. The drug of choice is alemtuzumab (Lemtrada), either alone or in combination with other drugs.

The response rate to this drug is as high as 90 percent, with up to 80 percent of people achieving complete remission. Although the response to first time chemotherapy can be good, relapse usually occurs within 2 years of remission.

For anyone in complete remission, an allogenic stem cell transplant — which can involve donations from bone marrow or blood — will be considered. However, finding a suitable donor can be difficult.

If there’s no donor available, an autologous stem cell transplant — which is a sample collected from you before chemotherapy — may be a good option.

T-PLL is a very aggressive type of leukemia. On average, people with T-PLL live about 20 months after diagnosis. This hasn’t changed significantly in over 30 years, even as newer and better treatments have become available.

When relapse occurs, remission can be achieved again using a “plan b” medication or treatment option, but it typically lasts only 6 to 9 months.

Although it’s a rare disease, T-PLL is one of the most common T-cell leukemias. It’s very aggressive and requires treatment early on. The most common symptom of this T-cell leukemia is a very high white blood cell count.

The diagnosis is made by physical exam and various types of blood tests to determine T-cell characteristics.

When you’re symptomatic, early treatment with intravenous chemotherapy is recommended. Stem cell transplant is considered for anyone who achieves complete remission.