Lymphoblastic lymphoma (LBL) is a neoplasm of immature B cells committed to the B-(B-LBL) or T-cell lineage (T-LBL) that accounts for approximately 2% of all lymphomas. From a histopathological point of view, blasts may be encountered in tissue biopsy and/or bone marrow (BM). In tissue sections, LBL is generally characterized by a diffuse or, as in lymph nodes and less commonly, paracortical pattern. Although histological features are usually sufficient to distinguish lymphoblastic from mature B- or T-cell neoplasms, a differential diagnosis with blastoid variant of mantle cell lymphoma, Burkitt lymphoma or myeloid leukemia may arise in some cases. Of greater importance is the characterization of immunophenotype by flow cytometry. In B-LBL, tumour cells are virtually always positive for B cell markers CD19, CD79a and CD22. They are positive for CD10, CD 24, PAX5, and TdT in most cases, while the expression of CD20 and the lineage independent stem cell antigen CD34 is variable and CD45 may be absent. Surface immunoglobulin is usually absent. In T-LBL, neoplastic cells are usually TdT positive and variably express CD1a, CD2, CD3, CD4, CD5, CD7 and CD8. The only reliable lineage-specific is surface CD3. Most B-LBL have clonal rearrangements of the Ig heavy chain or less frequently of light chain genes. T-cell receptor γ or β chain gene rearrangements may be seen in a significant number of cases, but rearrangements are not helpful for lineage assignment. LBL occurs more commonly in children than in adults, mostly in males. Although 80% of precursor B-cell neoplasms present as acute leukemias, with BM and peripheral blood (PB) involvement, a small proportion present with a mass lesion and have <25% blasts in the BM. Unlike precursor T-LBL, mediastinal masses and involvement of BM are rare, but lymph nodes and extranodal sites are more frequently involved. T-LBL patients, compared to those with B-LBL, show younger age, a higher rate of mediastinal tumours or BM involvement. Patients are usually males in their teens to twenties and present with lymphadenopathy in cervical, supraclavicular and axillary regions, or with a mediastinal mass. In most patients the mediastinal mass is anterior, bulky, and associated with pleural effusions, superior vena cava syndrome, tracheal obstruction, and pericardial effusions. They frequently present with advanced disease, B symptoms and elevated serum LDH levels. Abdominal involvement (liver and spleen) is unusual. LBL is highly aggressive, but frequently curable with current therapy. The prognosis in all age groups has dramatically improved with the use of intensive ALL-type chemotherapy regimes, with a disease-free survival of 73-90% in children and 45-72% in adults. Intensive intrathecal chemotherapy prophylaxis is required to reduce the CNS relapse incidence, while the role of prophylactic cranial irradiation is unclear. Consolidation mediastinal irradiation may decrease mediastinal relapse. Patients with adverse prognostic features should be considered for high-dose chemotherapy and SCT. Autologous SCT has been shown to produce similar good results as chemotherapy alone, and allogeneic SCT is likely to be a more appropriate option for patients who are beyond first remission or with more advanced disease.
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