Guidelines on Diagnosis and Treatment of Malignant Lymphomas

Mediastinal (Thymic)
Large B-Cell Lymphoma
Definition and incidence
Mediastinal (thymic) large B-cell lymphoma (med-DLBCL) is a
subtype of DLBCL of putative thymic B-cell origin arising in the
mediastinum which has distinctive clinical, immunophenotypic
and genetic features. It primarily affects people in the third or
fourth decades with a female:male ratio of 2-4:1 and has an
incidence rate of .25/100,000/year.
ICD – O Code 9679/3
Clinical Presentation
Patients present with localized disease and signs and symptoms
related to large anterior mediastinal masses, sometimes with
superior vena cava obstruction, pleural and/or pericardial
effusions. Disease at extranodal sites is frequently present at
relapse involving the CNS, liver, adrenal glands, kidneys and
gastrointestinal tract.
Pathology and Genetics
There is marked diffuse lymphoid proliferation associated with
variably dense compartmentalizing fibrosis. Immunohistochemical
staining with cytokeratin markers may identify thymic remnants
and resemble carcinoma. The neoplastic cells are medium to
large sized cells, typically with abundant pale cytoplasm and
oval nuclei. Some cases exhibit more pleomorphic nuclei.
An admixture of benign small lymphocytes and eosinophils
may suggest Hodgkin Lymphoma and occasionally Med-DLCBCL
and Nodular Sclerosis Hodgkin Lymphoma (NSHL) may co-exist
as a composite lymphoma.
Immunophenotype
Med-DLBCL expresses CD45 (CLA) and classical B-cell markers
such as CD19 and CD20. CD30 is expressed in >80% of cases
but is often weak and heterogenous. CD15 is usually negative,
IRF4/MUM1 and CD23 are positive in >75% of cases. CD10 is
rarely positive (