—  SHORT COURSE #63  —

A Practical Approach to the Diagnosis of Common Hematopoietic and Solid Tumors of Childhood

Case 10 - Mediastinal (Thymic) Large B-cell Lymphoma

D. Ashley Hill, M.D.
Mihaela Onciu M.D.


Case History:
14-year-old girl with large anterior mediastinal mass and cervical lymphadenopathy. An incisional biopsy of the cervical lymph node was performed.

Microscopic Findings:
Several fragments of lymph node showed complete effacement of the normal architecture by a malignant lymphoid neoplasm with diffuse growth pattern and associated fine bands of sclerosis. The neoplastic cells were relatively monotonous, large, with abundant pale to clear cytoplasm, irregular nuclear outlines, coarsely clumped and marginated nuclear chromatin and prominent nucleoli. Occasional cells showed markedly convoluted 'floral' nuclear outlines. Scattered mitotic figures were noted.

Differential Diagnosis:
  1. Diffuse large B-cell lymphoma

  2. Anaplastic large cell lymphoma (common or monomorphic variant).

  3. Hodgkin disease, nodular sclerosis, syncytial

  4. Metastatic non-hematopoietic tumor (e.g. germ cell tumor).

Immunophenotypic Findings (Immunohistochemistry):
The lymphoma cells were strongly positive for CD45, and CD20, and variably positive for CD30. They were negative for CD3, CD10 and CD15.

Molecular/Cytogenetic Analysis:
Not performed.

Diagnosis:
Diffuse large B-cell lymphoma, mediastinal (thymic) type (the latter subclassification was supported by the clear-cell morphology and the associated large mediastinal mass).

Diffuse Large B-Cell Lymphoma (DLBCL)


Definition:
In the WHO classification DLBCL is a mature B-cell neoplasm with diffuse growth pattern composed of large lymphoma cells (i.e. larger than the normal macrophage nuclei). Several morphologic variants are accepted (all of which may be encountered in children). These variants include: centroblastic, immunoblastic, T-cell/histiocyte rich, and anaplastic.

The mediastinal (thymic) large B-cell lymphoma is defined as a subtype of DLBCL which arises in the mediastinum and has distinctive clinical, immunophenotypic and genotypic features that may be related to its origin in a putative thymic B-cell.

Epidemiology:
DLBCL represents 30-40% of the adult non-Hodgkin lymphomas (NHL) and ~10% of pediatric NHL. Mediastinal DLBCL occurs predominantly in the third and fourth decades of life, with a striking female predominance. In the pediatric age group these tumors are seen almost exclusively in teenage girls.

Clinical Features:
DLBCL presents presents as lymphadenopathy or extranodal tissue masses (40%). The most common extranodal site is the gastrointestinal tract (gastric or ileo-cecal regions). In many cases of pediatric primary gastric DLBCL an association with Helicobacter pylori has been documented (more frequent in developing countries), with or without an associated low-grade MALT-type component. Mediastinal DLBCL characteristically presents as a bulky mediastinal mass, often with associated shotness of breath, coughing or even superior vena cava syndrome. When extra-thoracic dissemination occurs, this lymphoma less commonly involves lymph nodes and more often affects extra-nodal sites such as kidney, skin and lungs. Bone marrow involvement by this lymphoma is exceptional.

Molecular Biology and Cytogenetics:
DLBCL may present as a de novo lymphoma or as progression of a pre-existing low-grade lymphoma. In children de novo DLBCL is the more common occurrence. In a small percentage of cases a pre-existing follicular lymphoma component may be identified. Distinct genetic lesions have not been identified in the de novo cases. When cytogenetic studies are performed, these tumors typically show complex chromosomal abnormalities. Immunophenotypic and genetic studies including gene expression profiling have suggested that DLBCL is a biologically heterogeneous group of neoplasms, some of which have post-germinal center B-cell differentiation (CD10+, BCL-6+), while some resemble activated peripheral blood B-cells (CD10-, BCL-6-). These subgroups appear to have prognostic significance (better prognosis in the germinal center-like DLBCL). Mediastinal DLBCL is thought to originate in a thymic B-cell that does not normally recirculate as other mature B-lymphocytes. This hypothesis might explain its peculiar pattern of dissemination. The mediastinal lymphoma cells may show REL gene amplification and gains on chromosome 9p, abnormalities that appear to be unique to this DLBCL subtype. Recent studies using gene expression profiling have suggested further heterogeneity within this group of tumors, that may include a subtype that resemble Hodgkin lymphoma and a subtype that is closer to other DLBCL.

Morphologic Features:
DLBCL is a tumor with diffuse growth pattern composed in variable proportions of several types of large lymphoma cells that include centroblasts, immunoblasts, and anaplastic cells. The predominance of one or another type is associated with the various morphologic subtypes. Centroblasts are medium-sized to large cells with scanty cytoplasm, irregular nuclear outlines, vesicular chromatin and several peripherally-located nuclei. Immunoblasts are large cells with abundant basophilic cytoplasm, vesicular or clumped chromatin, eccentric nuclei and single centrally-located nucleoli. Anaplastic cells are similar to those seen in ALCL and include giant cells with pleomorphic nuclei or Reed-Sternberg-like morphology. In the centroblastic variant the tumor consists of a polymorphous mixture of centroblasts and immunoblasts, with <90% immunoblasts. In the immunoblastic variant >90% of the lymphoma cells are immunoblasts. In the anaplastic variant frequent anaplastic cells are admixed with centroblasts and immunoblasts. Occasionally, a cohesive growth pattern may be present. In T-cell/histiocyte-rich B-cell lymphoma the bulk of the tumor consists of inflammatory cells, while the neoplastic cells (centroblasts, immunoblasts, Reed-Sternberg-like) represent <10% of cellularity. Mediastinal DLBCL can present as any of these variants. In addition, in the latter, lymphoma cells may have a characteristic "clear-cell appearance", with abundant, pale or clear cytoplasm. All types of DLBCL may be associated with prominent fibrosis, more frequent in the mediastinal variant.

Immunophenotype:
In all subtypes of DLBCL the lymphoma cells strongly express CD45 and CD20, as well as other B-cell antigens, such as CD19, CD22, and CD24. A subset of DLBCL may express CD10, BCL-6, and BCL-2 (resembling follicle center cell lymphoma). Occasional DLBCL are positive for CD5. Light chain restricted immunoglobulin expression may be demonstrated in many cases, although a significant proportion of these lymphomas may lack immunophenotypic evidence of immunoglobulin expression. Such cases show clonal rearrangements of the immunoglobulin genes when analyzed by molecular means. Mediastinal large B-cell lymphomas are usually CD45+, CD20+, CD30+, CD5-, CD10-, BCL-2 -, BCL-6 -, and lack immunoglobulin and HLA class I expression.

Differential Diagnosis:
(See tables 6.4, 7.2, and 10.1) DLBCL, any subtype:
  1. Burkitt lymphoma

  2. Precursor B-cell lymphoblastic lymphoma
DLBCL, anaplastic:
  1. Anaplastic large cell lymphoma of T/null cell lineage

  2. Non-hematopoietic tumors metastatic to lymph nodes (melanoma, carcinoma, germ cell tumor)

  3. Hodgkin lymphoma (syncytial variant)
T-cell/histiocyte rich DLBCL:
  1. Nodular lymphocyte predominance Hodgkin lymphoma

  2. Classical Hodgkin lymphoma

  3. 'Grey-zone' lymphoma
Mediastinal DLBCL
  1. Hodgkin lymphoma, nodular sclerosis subtype

  2. Thymic carcinoma/malignant thymoma

  3. Germ cell tumor

  4. Primary sclerosing mediastinitis

  5. Precursor T-cell lymphoblastic lymphoma
Table 10.1: Immunohistochemical Staining in the Differential Diagnosis of Anterior Mediastinal Masses in Pediatric Patients

Tumor type CK Tdt CD3 CD15 CD20 CD30 CD45 PLAP HCG
T-LBL - + + - - - +
(weak) 		_ _
Thymoma +
(ep) 		- +
(ly) 		- - - +
(ly, strong) 		- -
Hodgkin lymphoma - - - + -/+ + - - -
DLBCL - - - - + +
(weak) 		+
(strong) 		- -
Germ cell tumor -/+ - - - - -/+ - + -/+

T-LBL – precursor T-cell lymphoblastic lymphoma, DLBCL - diffuse large B-cell lymphoma, CK – cytokeratin, ep – epithelial component, ly - lymphocytes.

Recommended Reading:

Lymphoma Classification and All Lymphoma Categories:
  • Jaffe ES, Harris NL, Vardiman JW, eds. World Health Organization Classification of Tumours. Pathology and genetics of tumours of haematopoietic and lymphoid tissues. Lyon: IARC Press; 2001.

  • Jaffe ES, Harris NL, Vardiman JW, eds. World Health Organization Classification of Tumours. Pathology and genetics of tumours of haematopoietic and lymphoid tissues. Lyon: IARC Press; 2001.

  • Jaffe ES, Harris NL, Vardiman JW, eds. World Health Organization Classification of Tumours. Pathology and genetics of tumours of haematopoietic and lymphoid tissues. Lyon: IARC Press; 2001.

Anaplastic Large Cell Lymphoma
  • Jaffe ES. Anaplastic large cell lymphoma:the shifting sands of diagnostic Hematopathology. Mod Pathol. 2001;14:219.

  • Benharroch D, Meguerian-Bedoyan Z, Lamant L, Amin C, Brugières L, Terrier-Lacombe M-J et al. ALK-positive lymphoma:a single disease with a broad spectrum of morphology. Blood. 1998;91:2076.

  • Falini B, Bigerna B, Fizzotti M, Pulford K, Pileri SA, Delsol G. ALK expression defines a distinct group of T/null lymphomas ("ALK lymphomas") with a wide morphological spectrum. Am J Pathol. 1998;153:875.

  • Chott A, Kaserer K, Augustin I, Vesely M, Heinz R, Oehlinger W, Hanak H, Radaszkiewicz T. Ki-1 positive anaplastic large cell lymphoma. A clinicopathologic study of 41 cases. Am J Surg Pathol. 1990;14:439.

  • Downing JR, Shurtleff SA, Zielenska M, Curcio-Brint AM, Behm FG, Head DR et al. Molecular detection of the t(2;5) translocation of non-Hodgkin's lymphoma by reverse transcriptase-polymerase chain reaction. Blood. 1995;85:3416.

  • Agnarsson BA, Kadin ME. Ki-1 positive large cell lymphoma: a morphologic and immunologic study of 19 cases. Am J Surg Pathol. 1988;12:264.

  • Kinney MC, Collins RD, Greer JP, Whitlock JA, Sioutos N, and Kadin ME. A small-cell-predominant variant of primary Ki-1 (CD30)+ T-cell lymphoma. Am J Surg Pathol. 1993; 17:859.

  • Onciu M, Behm, FG, Raimondi, SC et al. ALK-positive anaplastic large cell lymphoma with leukemic peripheral blood involvement is a clinicopathologic entity with an unfavorable prognosis. Report of three cases and review of the literature. Am J Clin Pathol 2003;120:617-625.

  • Pileri S, Falini B, Delsol G et al. Lymphohistiocytic T-cell lymphoma (anaplastic large cell lymphoma CD30+/Ki-1+ with a high content of reactive histiocytes). Histopathology. 1990;16:383.

  • Chan JKC, Buchanan R, Fletcher CDM. Sarcomatoid variant of anaplastic large cell lymphoma. Am J Surg Pathol. 1990;14:983.

  • McCluggage WG, Walsh MY, Bharucha H. Anaplastic large cell malignant lymphoma with extensive eosinophilic or neutrophilic infiltration. Histopathology. 1998;32:110.

  • Fallini B, Liso A, Pasqualucci L, et al. CD30+ anaplastic large cell lymphoma, null type, with signet-ring appearance. Histopathology. 1997;30:90.

  • Juco J, Holden JT, Mann KP, Kelley LG, Li S. Immunophenotypic analysis of anaplastic large cell lymphoma by flow cytometry. Am J Clin Pathol. 2003;119:205.

Burkitt Lymphoma
  • Hecht JL, Aster JC. Molecular biology of Burkitt's lymphoma. J Clin Oncol. 2000; 18:3707.

  • Cairo MS, Sposto R, Perkins SL et al. Burkitt's and Burkitt-like lymphoma in children and adolescents: a review of the Children's Cancer Group experience. Br J Haematol. 2003.;120: 660.

  • Lones MA, Auperin A, Raphael M Mature B-cell lymphoma/leukemia in children and adolescents: intergroup pathologist consensus with the revised European-American Lymphoma Classification Ann Oncol. 2000; 11: 47.

Lymphoblastic Lymphoma/Leukemia
  • Pui C-H, Crist WM. Acute lymphoblastic leukemia. In Pui C-H, ed. Childhood leukemias. Cambridge University Press, New York, NY, 1999, p.288.

Diffuse Large B-Cell Lymphoma
  • Cairo MS, Sposto R, Hoover-Regan M et al. Childhood and adolescent large-cell lymphoma (LCL): a review of the Children's Cancer Group experience. Am J Hematol. 2003; 72: 53.

  • Abou-Elella AA, Weisenburger DD, Vose JM, et al. Primary mediastinal large B-cell lymphoma: a clinicopathologic study of 43 patients from the Nebraska Lymphoma Study Group. J Clin Oncol. 1999;17:784.

  • Davis RE, Dorfman RF, Warnke RA. Primary large-cell lymphoma of the tymus: a diffuse B-cell neoplasm presenting as primary mediastinal lymphoma. Hum Pathol. 1990; 21:1262.

  • Lones MA, Perkins SL, Sposto R et al. Large-cell lymphoma arising in the mediastinum in children and adolescents is associated with an excellent outcome: a Children's Cancer Group report. J Clin Oncol. 2000; 18: 3845.