T-cell acute lymphoblastic leukemia (T-ALL) is a type of blood cancer that begins in the bone marrow and can spread to other organs. It is one of two forms of acute lymphoblastic leukemia (ALL), the most common childhood cancer.

Doctors diagnose around 6,600 individuals with ALL annually. T-ALL accounts for approximately 12–15% of child cases and up to 25% of adult cases of ALL. Although more common in adults than children, its incidence decreases with age.

In this article, we explore T-ALL and its symptoms. We also examine the potential treatments and outlook for the condition and compare it to other forms of leukemia.

T-ALL is a fast-growing blood cancer that progresses quickly. Doctors may also call it precursor T-lymphoblastic leukemia or T-cell acute lymphocytic leukemia.

T-ALL affects the stem cells in the bone marrow that produce lymphoid cells. In this case, white blood cells are called T lymphocytes. T lymphocytes are immune cells that help keep a person healthy by directly killing cells carrying infections, activating other immune cells, and regulating the immune response with chemicals called cytokines.

In people with T-ALL, at least 20% of the white blood cells in the bone marrow or blood are atypical. And those with under 20% of these cells may have a similar condition called T-lymphoblastic lymphoma, which doctors manage with similar treatments.

In T-ALL, the immature white blood cells accumulate in the bone marrow and crowd out healthy white blood cells, weakening the immune system. The cells may also build up in the liver, spleen, and lymph nodes.

The most common symptoms of T-ALL are nonspecific. Therefore, doctors may find distinguishing the condition from typical childhood diseases challenging.

T-ALL results in fewer healthy blood cells, so it may cause generalized symptoms such as:

An individual with T-ALL may also develop swollen lymph nodes in the middle of their chest, affecting their breathing or circulation.

Doctors often treat T-ALL with multidrug chemotherapy and steroids for 2–3 years. These chemotherapy agents include medications that kill cancer cells or stop them from dividing.

Doctors usually administer chemotherapy in cycles of treatment comprising a series of dosages of the chemotherapy medication before a recovery period.

If tests reveal that T-ALL cells are in the fluid surrounding the brain and spine, doctors may inject chemotherapy agents into these areas, which is a treatment called intrathecal chemotherapy. Individuals may also receive cranial radiation therapy.

The exact schedule and type of chemotherapy depend on the individual’s age and general health.

If chemotherapy is unsuccessful and the individual is young and fit, doctors may suggest a stem cell transplant, also known as a bone marrow transplant.

First, the individual undergoes chemotherapy or radiation to kill cancer cells and suppress the immune system. They then receive an infusion of healthy bone marrow cells that travel through the blood and into the bone marrow. Eventually, these new cells should multiply and begin making healthy blood cells.

The outlook for an individual with T-ALL is generally good. Children have an overall survival rate of more than 85% after 5 years, although this figure is less than 50% in adults. One reason for this could be that children may handle high levels of chemotherapy more effectively than adults.

However, some research shows that this 5-year survival rate may drop to around 7% in individuals who relapse or do not respond well to treatment. Around 1 in 5 children and 2 in 5 adults relapse, with 80% of these relapses occurring within 2 years of diagnosis.

Certain risk factors increase an individual’s risk of T-ALL, including:

  • Age: Although most types of leukemia are common in older individuals, ALL leukemias are the exception. ALL occurs most commonly in children aged 2–5 years, while T-ALL is most common in slightly older children.
  • Biological sex: T-ALL affects males more than females.

There are also a few known risk factors for ALL in general, including:

  • radiation exposure
  • chemical exposure, such as chemotherapy drugs and benzene
  • viral infections, such as human T-cell lymphoma/leukemia virus 1 and Epstein-Barr virus
  • genetic syndromes, such as Down syndrome and Fanconi anemia
  • race, as ALL is more common in white people

Doctors classify various forms of leukemia according to the type of cells they affect and how quickly the disease progresses. The following information explores the similarities and differences between T-ALL and other types of leukemia.

B-cell ALL

B-cell ALL is the other form of ALL. Like T-ALL, it is a fast-growing cancer that affects the lymphoblasts. However, it tends to affect younger children.

Leukemia starts in the early forms of B cells rather than T cells in most children with ALL.

B-cell ALL has several subtypes, including mature B-cell ALL or Burkitt’s leukemia.

Learn more about B-cell ALL.

Acute myeloid leukemia (AML)

Like T-ALL, AML is a fast-growing blood cancer. However, it develops in the following different bone marrow cells:

  • Myeloblasts: These form neutrophils, eosinophils, and basophils, which are white blood cells called granulocytes.
  • Monoblasts: These become white blood cells called monocytes and macrophages.
  • Erythroblasts: These mature into red blood cells.
  • Megakaryoblasts: These transform into megakaryocytes, the cells that make platelets.

AML has various subtypes, including acute promyelocytic leukemia. Doctors classify these leukemias depending on the cells it affects and the types of genetic changes they feature.

Unlike T-ALL, AML typically affects adults and is more common.

Learn more about AML.

Chronic myeloid leukemia (CML)

CML is a slow-growing cancer of immature or myeloid bone marrow cells. It commonly affects adults, but it can also develop in children.

CML differs from T-ALL in that it has three phases depending on the number of immature white blood cells or blasts identifiable in the blood or bone marrow.

The early, chronic phase causes only mild symptoms. However, the accelerated phase, where atypical cells are more common, may cause:

The accelerated phase may not respond as well to treatment.

The final phase of CML is the blast phase, where leukemia cells have spread outside the bone marrow, and the disease resembles aggressive acute leukemia such as AML or ALL.

Learn more about CML.

T-ALL is a blood cancer that results in the body producing high levels of atypical or immature T cells. These cells then crowd out the healthy blood cells that form part of the immune system.

Because the condition compromises the immune system, it can lead to an increased risk of infections and other symptoms such as bleeding issues and severe fatigue.

Doctors treat T-ALL with chemotherapy, and they may recommend bone marrow transplants, depending on an individual’s health.

Many children with T-ALL have a good outlook, with 5-year survival rates of more than 85%, but this figure drops to 50% in adults.

Research is ongoing to find new ways to treat and manage this challenging condition.