Lymphoblastic Lymphoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC and Aleksandra Paliga MD FRCPC
April 21, 2026

Lymphoblastic lymphoma is an aggressive cancer of the immune system that starts in immature lymphocytes called lymphoblasts. Lymphoblasts are the earliest, most immature form of lymphocytes — the white blood cells that normally mature into either B cells (which make antibodies) or T cells (which coordinate immune responses and kill infected cells). In lymphoblastic lymphoma, lymphoblasts fail to mature normally and instead multiply uncontrollably, forming masses in the lymph nodes, thymus, and other tissues. Lymphoblastic lymphoma is closely related to acute lymphoblastic leukemia (ALL) — in fact, they are caused by the same type of abnormal cell. The difference is anatomical: in lymphoblastic lymphoma, the abnormal cells grow primarily as solid masses in tissues with minimal involvement of the blood and bone marrow, while in ALL they proliferate predominantly in the blood and bone marrow. When lymphoma and leukemia features are both present, the disease is classified based on the degree of bone marrow involvement. This article provides an overview of lymphoblastic lymphoma to help you understand your diagnosis, and links to detailed articles for each subtype.

What are the types of lymphoblastic lymphoma?

Lymphoblastic lymphoma is classified based on whether the lymphoblasts originate from T cell precursors or B cell precursors — two distinct developmental lines that give rise to all lymphocytes. This distinction matters because T-LBL and B-LBL have different typical presentations, different sites of involvement, and slightly different treatment considerations.

T-cell lymphoblastic lymphoma (T-LBL)

T-cell lymphoblastic lymphoma (T-LBL) accounts for approximately 85–90% of all lymphoblastic lymphoma cases and is the most common type. It arises from immature T cell precursors — cells that would normally mature inside the thymus into functional T cells. Reflecting this thymic origin, T-LBL characteristically presents with a large mass in the mediastinum (the area of the chest between the lungs, where the thymus sits), which can cause cough, chest pressure, and shortness of breath. T-LBL most commonly affects adolescents and young adults and is more common in males than females. For full details about T-LBL including microscopic features, immunohistochemistry, genetic testing, staging, and treatment, see the dedicated article: T-Cell Lymphoblastic Lymphoma (T-LBL): Understanding Your Pathology Report.

B-cell lymphoblastic lymphoma (B-LBL)

B-cell lymphoblastic lymphoma (B-LBL) accounts for approximately 10–15% of all lymphoblastic lymphoma cases. It arises from immature B cell precursors and most commonly presents with lymph node masses in the head and neck region, skin involvement, or bone involvement rather than the mediastinal mass typical of T-LBL. B-LBL occurs across a wider age range, including young children. For full details about B-LBL including immunohistochemistry, genetic testing, and treatment, see the dedicated article: B-Cell Lymphoblastic Lymphoma (B-LBL): Understanding Your Pathology Report.

How are the two types different?

  • Cell of origin — T-LBL arises from immature T cell precursors that have entered the thymus; B-LBL arises from immature B cell precursors in the bone marrow or lymph nodes.
  • Typical location — T-LBL characteristically presents with a mediastinal (chest) mass; B-LBL most often involves lymph nodes of the head and neck, skin, or bone, without a mediastinal mass.
  • Age — Both affect children, adolescents, and young adults, but T-LBL has a stronger predilection for adolescent males; B-LBL occurs more evenly across the pediatric age range.
  • Protein markers — T-LBL cells express T cell proteins (CD3, CD7, CD2) and markers of immaturity (TdT, CD34). B-LBL cells express B cell proteins (CD19, CD79a, PAX5) and markers of immaturity (TdT, CD10). Both types are defined by TdT positivity, which identifies cells as immature lymphoblasts and distinguishes this disease from mature lymphomas.
  • Treatment and prognosis — Both are treated with similar intensive ALL-type chemotherapy protocols. Prognosis is excellent in children and good but somewhat less favorable in adults for both types.

Who gets lymphoblastic lymphoma?

Lymphoblastic lymphoma is most commonly diagnosed in children, adolescents, and young adults, though it can occur at any age. The median age at diagnosis is approximately 20 years. It is more common in males than females, particularly for T-LBL in adolescents. Together, T-LBL and B-LBL represent the second most common lymphoma in children and young adults, after Hodgkin lymphoma. In older adults, lymphoblastic lymphoma is uncommon but does occur and is treated with the same intensive approach.

What are the symptoms of lymphoblastic lymphoma?

Symptoms depend on the type and location of the lymphoma. The most characteristic and often dramatic presentation of T-LBL is a large mass in the mediastinum — the space in the chest behind the breastbone and between the lungs. This mass can grow rapidly and cause cough, shortness of breath, a sense of chest pressure or tightness, and swelling of the face, neck, and arms (called superior vena cava syndrome) if it compresses the large blood vessel that returns blood from the upper body to the heart. The mediastinal mass is sometimes discovered on a chest X-ray performed for an unrelated reason.

In B-LBL, the most common presentation is painless swollen lymph nodes in the neck, armpits, or groin, sometimes accompanied by bone pain, skin nodules, or an abdominal mass. Both types may cause generalized symptoms including fever, drenching night sweats, significant weight loss, and fatigue — collectively called B symptoms.

Spread to the central nervous system (CNS) — the brain and spinal fluid — is an important concern in both T-LBL and B-LBL. CNS involvement can cause headache, visual changes, cranial nerve palsies, or other neurological symptoms. Because CNS spread affects treatment planning, lumbar puncture (sampling of the spinal fluid) is performed as part of the standard staging evaluation in all patients.

Because lymphoblastic lymphoma is aggressive and grows rapidly, symptoms often worsen quickly over days to weeks, and the diagnosis is typically made urgently. Patients may require admission to hospital for initial management of complications, including urgent relief of mediastinal compression when present.

What causes lymphoblastic lymphoma?

Lymphoblastic lymphoma arises from acquired genetic changes in immature lymphoid precursor cells that cause them to stop maturing normally and instead proliferate uncontrollably. These changes occur in the cell’s DNA during the complex process of lymphocyte development, which involves an extraordinarily large number of DNA rearrangements as cells create unique antigen receptors. This process creates opportunities for errors — some of which can, in rare cases, activate cancer-driving genes or disable genes that normally suppress cell growth.

In T-LBL, genetic changes frequently involve genes that regulate T cell development in the thymus, including NOTCH1 mutations (found in approximately 50–60% of cases), which drive lymphoblast proliferation. In B-LBL, a wide variety of chromosomal rearrangements are found, and genetic subtyping of B-LBL closely mirrors that of B-ALL, with some subtypes associated with excellent outcomes and others requiring more intensive treatment.

Specific risk factors are identified in only a minority of patients. Down syndrome is associated with a significantly elevated risk of B-lymphoblastic leukemia/lymphoma. Prior exposure to certain chemotherapy agents or ionizing radiation increases risk. Inherited conditions affecting DNA repair or immune function also confer higher risk. However, the majority of patients who develop lymphoblastic lymphoma have no identifiable predisposing condition.

How is the diagnosis made?

The diagnosis of lymphoblastic lymphoma requires tissue examination under the microscope. A biopsy of an affected lymph node or mass is performed, most commonly by excisional biopsy (removal of a lymph node) or core needle biopsy. When bone marrow is involved, a bone marrow biopsy is also performed. The pathologist examines the tissue and performs immunohistochemistry (IHC) and flow cytometry to identify the protein profile of the abnormal cells. The single most important diagnostic finding is positivity for TdT (terminal deoxynucleotidyl transferase) — a protein present only in immature lymphoid precursor cells (lymphoblasts) and absent from all mature lymphocytes. TdT positivity is the defining feature that distinguishes lymphoblastic lymphoma from all mature B cell and T cell lymphomas.

Additional tests — including FISH (fluorescence in situ hybridization) and next-generation sequencing — are performed to identify specific chromosomal abnormalities and gene mutations that subclassify the disease, carry prognostic significance, and identify potential targets for therapy. These genetic results are increasingly important for treatment planning and are discussed in the subtype-specific articles.

An important distinction must be established at diagnosis: whether the disease is predominantly lymphoma (solid masses, bone marrow involvement below 25% blasts) or leukemia (bone marrow involvement of 25% or more blasts, which meets the definition of ALL). This boundary affects how the disease is classified and staged, though treatment is similar in both cases.

What does lymphoblastic lymphoma look like under the microscope?

Under the microscope, lymphoblastic lymphoma has a distinctive appearance that reflects the immature nature of the cells. The lymph node or affected tissue is typically diffusely replaced — effaced — by a uniform population of small to medium-sized cells with very little cytoplasm (the material surrounding the nucleus). The nuclei are round to irregular or convoluted in shape (particularly in T-LBL, where convoluted nuclei are a characteristic feature), with finely dispersed, delicate chromatin — the pattern of DNA inside the nucleus — which gives the nuclei a pale, powdery appearance rather than the densely clumped pattern seen in mature lymphocytes. Nucleoli (dense structures inside the nucleus) are inconspicuous or absent. Mitotic figures — cells caught in the act of dividing — are numerous, reflecting the rapid proliferation of the lymphoma.

The high ratio of nucleus to cytoplasm — meaning almost the entire cell is occupied by the nucleus with virtually no surrounding cytoplasm — is one of the most recognizable features of lymphoblasts under the microscope. A starry sky pattern (pale macrophages scattered through a dark sea of tumor cells) may be visible, reflecting the high rate of cell death accompanying the rapid proliferation, though this is less pronounced than in Burkitt lymphoma.

What is TdT, and why does it matter?

TdT (terminal deoxynucleotidyl transferase) is an enzyme that is present only in immature lymphoid cells — the precursor cells that have not yet finished developing into mature B cells or T cells. Normal mature lymphocytes, plasma cells, NK cells, and all other mature immune cells do not express TdT. Because of this restricted expression, TdT positivity in a lymphoma is a strong indicator that the tumor cells are immature lymphoblasts rather than mature lymphocytes. This single finding has major clinical implications: it means the lymphoma should be treated with ALL-type intensive chemotherapy protocols rather than the CHOP-based regimens used for most mature lymphomas, which would be insufficient for lymphoblastic lymphoma. Whenever TdT positivity is found in a lymphoma biopsy, it immediately points the pathologist and treating physician toward the lymphoblastic lymphoma/leukemia category.

Staging

Lymphoblastic lymphoma is staged using the Murphy staging system (for children) or the Lugano classification (for adults). However, unlike many other lymphomas where stage is the primary driver of treatment decisions, in lymphoblastic lymphoma the most important factors guiding treatment intensity are the degree of bone marrow involvement, whether the CNS is involved, the specific genetic features of the lymphoma cells, and the patient’s response to initial therapy (assessed by minimal residual disease testing).

  • Stage I — A single tumor or single nodal group in one area, not involving the mediastinum or abdomen.
  • Stage II — A single tumor with regional lymph node involvement on the same side, or two tumors on the same side of the diaphragm, or a GI tumor with regional nodes.
  • Stage III — Tumors on both sides of the diaphragm, including mediastinal or abdominal disease; or CNS or bone marrow involvement with less than 25% blasts.
  • Stage IV — Bone marrow involvement with 25% or more blasts (at this threshold, the disease meets the definition of ALL).

The majority of patients present with advanced-stage (stage III) disease, including mediastinal mass and widespread lymph node involvement. CNS involvement at diagnosis — found in a small proportion of patients — requires intensification of CNS-directed treatment.

What is the prognosis?

Lymphoblastic lymphoma is highly treatable, particularly in children and young adults. With modern ALL-type chemotherapy protocols, children achieve complete remission rates exceeding 90–95% and long-term survival rates of 80–90% or more. Adult outcomes are somewhat less favorable, with long-term survival rates of approximately 50–70%, though results continue to improve as treatment is refined.

The most important prognostic factor — more than stage — is the response to initial treatment, particularly the achievement of minimal residual disease (MRD) negativity: the absence of detectable residual lymphoma cells by highly sensitive testing after induction chemotherapy. Patients who achieve deep MRD negativity early in treatment have significantly better outcomes than those with persistent detectable disease. Genetic features of the lymphoma cells also influence prognosis: certain chromosomal changes (such as ETV6::RUNX1 fusion in B-LBL) are associated with excellent outcomes, while others (such as Philadelphia chromosome-like ALL features or TP53 alterations) are associated with higher relapse risk and may require intensified treatment or transplantation.

What happens after the diagnosis?

Because lymphoblastic lymphoma is aggressive, treatment begins urgently — typically within days of diagnosis. Most patients are managed at centers with expertise in leukemia and lymphoma, and pediatric patients are ideally treated at or in consultation with specialized pediatric oncology centers.

Treatment follows ALL-type intensive chemotherapy protocols rather than the CHOP-based regimens used for most other lymphomas. These protocols are divided into three phases: induction (intensive initial chemotherapy to achieve remission, typically over four to six weeks), consolidation (further intensive treatment to eliminate residual disease, over several months), and maintenance (lower-intensity chemotherapy to prevent relapse, continuing for two to three years). CNS-directed treatment — delivered as intrathecal chemotherapy (medication injected into the spinal fluid) or high-dose systemic methotrexate — is an integral part of all protocols, because preventing CNS relapse is essential.

For patients with Philadelphia chromosome-positive B-LBL or Philadelphia chromosome-like features, targeted therapy with a tyrosine kinase inhibitor (such as imatinib or dasatinib) is added to chemotherapy. For patients who do not achieve adequate response to initial therapy or who relapse, intensification of treatment and autologous or allogeneic stem cell transplantation may be considered.

MRD testing — using highly sensitive flow cytometry or molecular testing of blood and bone marrow — is performed at multiple time points throughout treatment and is one of the primary tools used to guide treatment decisions and assess the need for intensification or transplantation.

Questions to ask your doctor

  • Is my lymphoblastic lymphoma of T cell or B cell type, and which specific subtype article should I read for more detailed information?
  • Was TdT positivity confirmed, and were all markers consistent with lymphoblastic lymphoma rather than a mature lymphoma?
  • Is my disease classified as lymphoma or leukemia based on the degree of bone marrow involvement?
  • Were genetic or chromosomal tests performed, and what did they show?
  • Has the disease spread to my central nervous system, and what does that mean for my treatment?
  • Which chemotherapy protocol is being recommended, and how long will treatment last?
  • How will MRD testing be used to monitor my response to treatment?
  • Am I a candidate for a clinical trial, and are there newer targeted therapies relevant to my genetic subtype?
  • Is stem cell transplantation being considered as part of my treatment plan?
  • What are the most important side effects I should watch for during treatment?
  • Should I consider fertility preservation before starting treatment?

Learn more about your specific type

For detailed information about your specific subtype — including full microscopic description, immunohistochemistry, genetic testing, staging, prognosis, and treatment — visit the dedicated articles below:

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