T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive form of blood cancer. It falls into a broader category of leukemia called acute lymphoblastic leukemia (ALL). ALL is the most common form of cancer in children. It’s most often diagnosed between ages 2 and 10.

About 6,000 people are diagnosed with ALL each year in the United States. T-ALL makes up about 12 to 15 percent of ALL cases in children and up to 25 percent of cases in adults.

The 5-year survival rates for T-ALL have steadily improved in recent years, reaching 85 percent in some clinical trials, according to 2016 research. However, the survival rate drops significantly in people whose cancer doesn’t respond to chemotherapy or relapses.

Keep reading to learn how T-ALL differs from other forms of leukemia, how it’s typically treated, and what your outlook may be with this condition.

Leukemia is a group of blood cancers. It happens when there are too many abnormal or immature blood cells in the blood-producing stem cells in your bone marrow.

These cancers are classified as acute leukemias if they progress quickly without treatment, or chronic leukemias if they spread slowly. They’re further classified into one of two categories, depending on which types of blood cells they affect:

  • Myeloid leukemias start in myeloid cells that become red blood cells, platelets, and a type of white blood cells called myeloblasts.
  • Lymphocytic leukemias start in lymphocytes that become three types of white blood cells: natural killer cells, T cells, and B cells.

The four main categories of leukemia are:

T-ALL is a subcategory of ALL. It primarily affects early forms of cells that become T-cells. T cells are a type of white blood cell that attacks foreign invaders and produces cytokines that activate other parts of your immune system.

In people with T-ALL, at least 20 percent of the white blood cells produced by bone marrow are not fully developed. These improperly developed white blood cells crowd out healthy blood cells and weaken your immune system.

It’s not entirely clear what causes T-ALL in some people but not others. However, some risk factors for ALL include:

  • radiation or chemical exposure
  • certain viral exposures
  • certain genetic syndromes

T-ALL has also been linked to genetic mutations in bone marrow stem cells.

People with T-ALL have fewer healthy white blood cells than usual and are more at risk of developing infections. T-ALL can also cause issues with blood clotting and bleeding disorders due to a low platelet count.

Commonly reported symptoms in people with ALL tend to be general and can include:

People with newly diagnosed T-ALL are usually treated with multidrug chemotherapy for 2 to 3 years, according to 2016 research.

You may receive cranial radiation therapy if the cancer enters your central nervous system. It’s more common for T-ALL to reach your central nervous system than for types of ALL that primarily affect B cells.

Chemotherapy is broken into three phases:

  • Induction. This phase tries to destroy as many cancer cells as possible and induce remission.
  • Consolidation and intensification. The goal here is to kill lingering cancer cells that may not be detectable.
  • Maintenance. This third phase aims to keep the cancer from coming back and is the longest of the phases.

Chemotherapy regimens can vary based on many individual factors, but often include:

  • anthracyclines such as daunorubicin or doxorubicin
  • steroids such as dexamethasone or prednisolone
  • vincristine with intrathecal methotrexate, which is injected into the spinal column to prevent cancer from spreading to your central nervous system
  • an intensification phase containing cyclophosphamide and cytarabine
  • L-asparaginase

Clinical trials from 2016 that compared the use of dexamethasone versus prednisone during the induction phase have that found dexamethasone reduces rates of relapse.

There’s no standard treatment for people who relapse, but the FLAG chemotherapy regimen is often used. It includes:

  • fludarabine
  • cytarabine
  • granulocyte colony-stimulating factor

Nelarabine is a drug specifically licensed for relapsed T-ALL that doesn’t respond to initial treatment. It can be effective, but about 15 percent of people who receive nelarabine develop neurotoxicity, which can cause severe and irreversible side effects.

Chemotherapy with bone marrow transplants

Some people with T-ALL receive a bone marrow transplant during the consolidation phase of treatment. This is done to replace bone marrow cells damaged during chemotherapy.

A procedure called an allogeneic transplant is often most effective. An allogeneic transplantation is when you receive bone marrow cells from a close relative or a compatible donor.

An autologous stem cell transplant may also be used if a donor isn’t available. This procedure involves removing your own healthy bone marrow cells before intense chemotherapy and reinfusing them once chemotherapy is finished.

Targeted therapies

Researchers are continuing to explore new treatment options for T-ALL and other forms of leukemia. One promising area of research is targeted therapies.

Targeted therapies are medications that identify and attack certain types of cancer cells. Unlike traditional chemotherapy, these drugs specifically target cancer cells and largely leave healthy cells intact.

Clinical trials are currently examining the potential benefit of different types of targeted therapy for T-ALL.

Many studies have found an overall survival rate for T-ALL of more than 85 percent in children, according to 2016 research. Survival in adult patients is less than 50 percent, mainly due to a decreased ability to handle high levels of chemotherapy compared to younger patients.

Research shows that people who don’t respond well to treatment or who relapse have a less promising outlook, with a survival rate of around 7 percent. About 20 percent of children and 40 percent of adults relapse, and 80 percent of relapses occur within 2 years of diagnosis.

T-ALL is a type of leukemia in which your body produces too many immature T-cells that crowd out healthy blood cells. It can cause a wide range of symptoms, including bleeding issues, suppressed immune system, and severe fatigue, among others.

The outlook for T-ALL is typically good in children, with some clinical trials reporting a survival rate of more than 85 percent. The survival rate in adults is less than 50 percent, but researchers are continuing to improve their understanding of T-ALL and the best ways to treat it.