T-cell acute lymphoblastic leukemia (T-ALL) is a fast-growing type of leukemia and a type of acute lymphoblastic leukemia (ALL). Also called T-cell acute lymphocytic leukemia or T-lymphoblastic leukemia, the condition develops from immature lymphocytes, a type of white blood cell.
About 5,700 people are diagnosed with ALL each year in the United States. ALL is the most common type of cancer in children, but it can occur in adults as well. Of all cases of ALL, about 10 percent to 25 percent are T-cell ALL.
Acute lymphoblastic leukemia develops when gene changes cause blood cells to grow out of control. Leukemias are divided into categories based on how fast they grow and which type of blood cell is affected. “Acute” means that the leukemia grows quickly, and “lymphoblastic” means that the leukemia develops from lymphoblasts. Lymphoblasts are immature lymphocytes — white blood cells that play different roles in helping the body fight infections.
ALL is further divided into subtypes depending on which type of lymphocyte is involved. The types of lymphocytes are B cells, T cells, and natural killer (NK) cells. T-ALL develops from T cells, which are responsible for activating the immune system and destroying other cells when they become infected.
Different subtypes of ALL tend to lead to the same sets of symptoms. These symptoms may include:
T-cell ALL also causes additional symptoms. Some people with this condition have an enlarged thymus (an organ behind the breastbone). An enlarged thymus may lead to breathing problems, coughing, or headaches.
By the time people are diagnosed with T-ALL, the leukemia cells have often spread to their central nervous system (CNS) — which includes the brain and spinal cord. When the brain is affected, T-cell ALL may cause headaches, blurry vision, and seizures.
If your doctor thinks you may have leukemia, they may prescribe tests to confirm a diagnosis. Blood tests are an important part of diagnosing leukemia. A test called a complete blood count measures the levels of each type of blood cell. Additional blood tests can identify possible problems with organs such as the kidneys or liver.
Most people with T-cell ALL need to have bone marrow tests. Bone marrow, the tissue found inside the bones, produces new blood cells. People with leukemia generally have many cancerous cells in their bone marrow. Testing the bone marrow helps a doctor diagnose blood cancer and identify which type of leukemia a person has. Bone marrow tests usually have two parts: During a bone marrow biopsy, a small sample of cells is removed from the bone. During a bone marrow aspiration, a sample of fluid is taken.
Cells from bone marrow and blood samples may be used for further laboratory testing. This may include cytogenetic tests to look at gene changes. A doctor may also use flow cytometry testing to look at a cell’s immunophenotype (proteins found on a cell’s surface). The information from these tests helps doctors determine effective treatments and estimate the prognosis (outlook) for a person’s particular condition.
Many people with ALL also need to have imaging tests. These can show if cancer cells have spread to certain organs and determine whether lymph nodes around the body are enlarged. Imaging tests might include:
Because T-ALL often spreads to the CNS, people with this condition will often require a lumbar puncture. During this procedure, doctors take a sample of fluid from the area around the spinal cord. They will then check this fluid for leukemia cells.
T-cell ALL is often treated in the same way as ALL that develops from B cells. However, people with T-ALL may be given more aggressive treatments.
When recommending a treatment plan, doctors will estimate a person’s risk level: high, standard, or low. This information helps doctors predict a person’s prognosis. People with T-cell ALL are usually classified as having a high-risk disease.
T-cell ALL is often treated with a combination of chemotherapy and steroid drugs. This treatment usually kills most of the leukemia cells. Chemotherapy is often given in multiple different phases: initial therapy, consolidation therapy, and maintenance therapy. During each phase, a person may receive different drugs at different doses. Initial and consolidation therapy phases may be more aggressive. Maintenance therapy often consists of low doses of chemotherapy drugs taken for two to three years.
Chemotherapy drugs that may be used to treat T-cell ALL include:
T-ALL is often treated with therapies that can prevent or treat the spread of leukemic cells to the central nervous system. These treatments often include intrathecal chemotherapy, in which chemotherapy drugs are injected into the fluid that surrounds the brain and spinal cord.
Targeted therapy drugs are sometimes given along with chemotherapy. These medications recognize and attack specific cancer genes or proteins. Most targeted therapies developed for ALL are used in B-cell ALL and won’t be effective against T-cell ALL. However, there are some options that may help certain people with T-ALL.
Arranon (nelarabine) is a targeted therapy drug approved by the U.S. Food and Drug Administration to treat T-cell ALL that is refractory (resistant to other treatments) or relapsed (came back after being treated with induction therapy). Nelarabine can help both children and adults have better outcomes. Now, researchers are also studying whether this drug may be helpful as a part of induction therapy for people undergoing treatment for the first time.
Some people with ALL have a gene change called the Philadelphia chromosome. Leukemia cells with this change can be targeted with tyrosine kinase inhibitors, a type of targeted therapy. These medications include Gleevec (imatinib), Sprycel (dasatinib), and Tasigna (nilotinib). However, this gene change is rare in T-cell subtypes of ALL.
If chemotherapy does not get rid of a person’s T-ALL cells, doctors may recommend stem cell transplantation. During this procedure, a person’s stem cells are replaced. Stem cells are the cells in the bone marrow that make new blood cells. A stem cell transplant consists of aggressive chemotherapy or radiation therapy treatments to kill as many leukemia cells as possible and make room in the bone marrow. This treatment is followed by an infusion of new stem cells, which replace damaged blood cells.
Overall, about 85 percent of people with T-ALL live for five years or more after being diagnosed. Children with T-ALL are likely to have better outcomes than adults. T-cell ALL can be cured (meaning all signs of leukemia disappear and don’t return) in about 4 out of 5 children. However, fewer than half of adult T-ALL cases can be cured.
One of the main factors that affects a person’s outlook is how well induction treatments work. If signs of cancer are gone at the end of induction therapy or at the end of consolidation therapy, a person usually has a good prognosis.
T-cell ALL is more likely to relapse than B-cell ALL. If T-ALL relapses, it is more difficult to treat. Therapies don’t often work as well, and people have an increased risk of having a worse outcome. People who have had multiple relapses may be able to try different chemotherapy drugs or participate in clinical trials.
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