Leukemias and Lymphomas of Thymic Differentiation

Primary Mediastinal Nodal and Extranodal Non-Hodgkin Lymphomas: Current Concepts, Historical Evolution, and Useful Diagnostic Approach: Part 2

Primary mediastinal non-Hodgkin lymphomas (PM-NHLs) represent ∼5% of all non-Hodgkin lymphomas (NHLs) and comprise lymphomas of B-cell and T-cell origin. PM-NHLs are defined as involvement of mediastinal lymph nodes, thymus, and/or mediastinal organs (heart, lung, pleura, pericardium) by NHL without evidence of systemic disease at presentation. The clinical scenario is variable and depends on the lymphoma subtype. The radiologic presentation is also variable ranging from a mediastinal mass with or without superior vena cava syndrome, a pleural or a cardiac mass associated with effusion, or as an effusion only. The diagnosis of PM-NHLs can only be established by microscopic evaluation, and therefore, general pathologists should be aware of these tumors and familiar with their diagnostic approach. The most common anterior mediastinal NHLs (90% to 95%) are primary mediastinal (PM) large B-cell lymphoma and T-lymphoblastic lymphoma. Thymic marginal zone lymphoma and mediastinal gray zone lymphoma are very rare. The remainder PM-NHLs involving middle or posterior mediastinum include diffuse large B-cell lymphoma (DLBCL) and rare cases of T-cell lymphoma, including anaplastic large cell lymphoma and breast implant-associated anaplastic large cell lymphoma extending to the anterior mediastinum. Primary pleural and cardiac NHLs are mostly DLBCLs. Other rare subtypes of PM-NHLs include DLBCL associated with chronic inflammation/pyothorax-associated lymphoma, fibrin-associated DLBCL (both Epstein-Barr virus positive), and pleural and/or pericardial primary effusion lymphoma (human herpesvirus-8 positive/Epstein-Barr virus positive). We review the historical aspects, epidemiology, clinicoradiologic features, histopathology, immunohistochemistry, differential diagnosis, and relevant cytogenetic and molecular features of the remaining mediastinal B-cell lymphomas, including primary thymic marginal zone lymphoma of the mucosa-associated lymphoid tissue type, other PM small B-cell lymphomas, PM plasmacytoma, and the most relevant PM T-cell lymphomas.

The rule of four: a systematic approach to diagnosis of common pediatric hematologic and oncologic disorders

The "Rule of Four" facilitates a rapid and focused approach to the diagnosis of the common hematologic and oncologic disorders encountered in general pediatric practice. This system relies on four recurrent but different clinical entities or laboratory tests relevant to the diagnosis of children with anemia, excessive bleeding or clotting, and common malignancies. For each disorder, there is a discussion of a variety of four lab tests or factors pertinent to a differential diagnosis.

Significance of aberrant immunophenotypes in childhood acute lymphoid leukemia

Leukemic cells from 51 pediatric patients (younger than 18 years) diagnosed with acute lymphoid leukemia by standard morphologic and cytochemical methods were subjected to flow cytometric studies using a panel of monoclonal antibodies against T-cell (CD1, 2, 3, 4, 5, 7, 8), B-cell (CD10, 19, 20, 21), myeloid (CD13, 14, 15, 33), and HLA-DR antigens. Cases of "conventional" acute lymphoid leukemia (leukemic cells with a normal configuration of B-cell or T-cell differentiation antigens) were observed in 26 of 51 (51%) cases, whereas cases of "aberrant" acute lymphoid leukemia (cells with abnormal patterns of B-cell or T-cell antigens or with concomitant myeloid antigens) were noticed in 25 (49%) cases. Myeloid antigen-positive acute lymphoid leukemia was observed in the leukemic cells of eight (16%) individuals. No significant differences were observed between conventional and aberrant ALL in the distribution of sex, age, leukocyte count, hemoglobin concentration, platelet count, blast count, French-American-British (FAB) type, lymphadenopathy, organomegaly, rate or duration of remission, or survival. When only myeloid antigen-positive cases were compared with myeloid antigen negative-cases, no significant correlations were observed except for duration of first remission (myeloid antigen positive, 26+ +/- 22 months; myeloid antigen negative, 40+ +/- 18 months; P less than 0.001), and duration of survival (myeloid antigen positive, 27+ +/- 24 months; myeloid antigen negative, 62+ +/- 17 months; P = 0.001). These data suggest that pediatric patients with ALL blasts possessing myeloid antigens may represent a high-risk group for length of remission and survival.

Multiple lineage reactivity in childhood leukemia

The leukemia cells from 63 children with acute leukemia were evaluated by flow cytometry with a panel of monoclonal antibodies that included lymphoid and myeloid lineage-specific antigens. Surface markers from patients with acute lyphocytic leukemia (ALL) did not correlate with their FAB classification except for L3 leukemia. Myeloid leukemias of FAB class M1-M4 were positive for CD13 and CD33, whereas CD14 and MY8 were only detected in FAB class M4 leukemia. Mixed leukemias were subclassified as intralineage (B+T+) or interlineage (B+ or T+/M+). Interlineage leukemias represented 5.6% of ALLs, and all patients are alive after treatment with ALL protocols. Interlineage mixed leukemias represent 7.9% of all leukemias occurring in 3.7% of ALLs and 33% of acute myeloid leukemias (AMLs). All children with mixed interlineage leukemias are alive after treatment with the protocol for the dominant leukemia; however, follow-up periods are too short to predict final outcome. The high proportion of mixed interlineage leukemias in AMLs supports Greaves' theory of lineage promiscuity, that is, there is a normal period of hematopoietic development when individual cells co-express multiple lineage antigens on the cell surface.