T-cell lymphoblastic lymphoma (T-LBL)

by David Li MD
December 13, 2024

This article is designed to help you understand your pathology report for T-cell lymphoblastic lymphoma. Each section explains an important aspect of the diagnosis and what it means for you.

What is T-cell lymphoblastic lymphoma?

T-cell lymphoblastic lymphoma (T-LBL) is a type of cancer caused by immature T cells called lymphoblasts. These are a type of white blood cell that normally helps the body fight infections. T-LBL is most common in children and teenagers but can also affect adults about 25% of the time. It accounts for 85–90% of all lymphoblastic lymphomas and is slightly more common in boys and young men, though it can develop in people of any gender or age.

What are the symptoms of T-cell lymphoblastic lymphoma?

The symptoms of T-LBL depend on where the disease is found in the body. Many patients have a large tumour in a part of the chest called the mediastinum, where the thymus and other organs are located. The presence of a large tumour in the mediastinum can cause:

• Shortness of breath, often due to fluid buildup around the lungs (pleural effusion) or the heart (pericardial effusion).
• A persistent cough or chest discomfort.

Other symptoms of T-LBL include:

• Feeling tired.
• Pain in the bones.
• Easy bruising or bleeding.
• Swelling in the abdomen due to an enlarged liver or spleen.

If you are experiencing any of these symptoms, your doctor may order tests to determine the cause.

What causes T-cell lymphoblastic lymphoma?

The exact cause of T-LBL is not fully understood, but doctors know that changes in specific genes can contribute to its development. These genetic changes allow cancer cells to grow and divide uncontrollably. Some factors that may increase the risk of developing T-LBL include:

• Exposure to harmful chemicals or radiation.
• Inherited genetic traits.
• A weakened immune system.

Although these factors can increase risk, many people who develop T-LBL have no identifiable cause.

What is the difference between T-cell lymphoblastic lymphoma and T-cell acute lymphoblastic leukemia?

T-LBL and T-cell acute lymphoblastic leukemia (T-ALL) are closely related. The main difference lies in where the cancer cells are found:

• T-ALL: The cancer cells are mostly in the blood and bone marrow.
• T-LBL: The cancer cells are found primarily in the lymph nodes, the thymus (a gland in the chest), or other body areas.

Because they are so similar, the diagnostic process and treatment for T-ALL and T-LBL often overlap.

How is this diagnosis made?

Doctors use several steps to diagnose T-LBL:

1. Medical history and physical exam: Your doctor will ask about your symptoms, medical history, and family history and perform a physical exam to look for signs of the disease.
2. Blood tests: A blood sample is checked for abnormal cells, including a complete blood count (CBC), to measure the numbers and types of blood cells.
3. Biopsies: A bone marrow or lymph node biopsy is often needed to confirm the diagnosis. In these procedures, a small sample of tissue is taken and examined under a microscope by a pathologist.
4. Genetic tests: Additional tests may look for changes in the cancer’s DNA to confirm the diagnosis and guide treatment.

What do the cancer cells look like under the microscope?

The cancer cells in T-LBL are immature T cells called lymphoblasts. These cells are immature because they have not fully developed into functional T cells. Normally, T cells mature in the bone marrow over several days, but in T-LBL, these cells remain immature and grow uncontrollably.

When examined under a microscope, these cancer cells appear round and purple. They look purple because the nucleus, the part of the cell that holds genetic material, takes up most of the space inside the cell. This makes the cytoplasm, or the “body” of the cell, appear very small. Pathologists describe this as a high nucleus-to-cytoplasm (N:C) ratio, which is a common feature of lymphoblasts in T-LBL.

What tests help confirm the diagnosis?

Pathologists use several tests to diagnose T-LBL and to rule out other conditions:

• Flow cytometry: Flow cytometry examines cells based on the proteins they make. T-LBL cells usually show markers found on immature T cells, such as CD3, CD7, CD1a, CD4, and CD8. The results from flow cytometry help confirm the diagnosis and classify the cancer based on the stage of T cell development.
• Immunohistochemistry: Immunohistochemistry uses special stains to highlight proteins in the cancer cells. T-LBL cells often test positive for T cell markers like CD3 and CD7, as well as markers of immaturity like TdT and CD34. These stains help identify the cancer and distinguish it from other diseases.
• Genetic tests: These tests look for changes in the cancer’s DNA that drive its growth. Common genetic changes in T-LBL include:
  • Translocations: A translocation is a piece of DNA swapped between chromosomes. These often involve chromosomes 14q, 7q, and 7p.
  • Deletions: A deletion is a missing piece of DNA. A common deletion involves chromosome 9p.
  • Mutations: Mutations in the NOTCH1 and FBXW7 genes are often found in T-LBL. These changes can allow cancer cells to survive longer and divide more quickly than normal cells.

What is minimal residual disease (MRD)?

After treatment, some cancer cells may remain in the body. This is called minimal residual disease (MRD). Testing for MRD helps doctors see how well the treatment worked and whether additional therapy is needed. MRD tests are very sensitive and can detect even a single cancer cell among a million healthy cells.

Is T-cell lymphoblastic lymphoma staged like other cancers?

No, T-LBL is not staged like other solid tumours. Instead, doctors look at factors like age, genetic changes, and treatment response to understand how the disease may behave. Children with T-LBL have a higher survival rate (80-90% for five years) than adults (around 50%).

What happens next?

After diagnosis, people with T-LBL are cared for by a team of specialists. Ongoing tests, like blood counts and bone marrow biopsies, monitor how well the treatment is working. MRD testing is important for tracking the disease and deciding if more treatment is needed.