Mediastinal (thymic) large B-cell lymphoma, Med-DLBCL

Definition

This is a subtype of diffuse large B-cell lymphoma arising in the mediastinum, with a distinct immunophenotype. The origin of this lymphoma is uncertain, but follicle centre cell, thymic and monocytoid B-cell derivations have all been suggested. The positivity for CD23 argues for an origin from activated dendritic thymic B cells3.

Epidemiology

It is relatively uncommon, accounting for 2.4% of all non-Hodgkin's lymphomas. It most commonly occurs in young adults (median 35 years), with a strong female predominance.

Clinical features

Patients usually present with an (anterior) mediastinal mass, which results in SVC obstruction in 25-30% of patients2. There is a tendency for spread to unusual sites.

Histopathology

The morphology is variable, but sclerosis, cells with relatively abundant clear or acidophilic cytoplasm, and multilobated nuclei are common features. The fibrosis is compartmentalizing. In most cases, the cells have abundant pale cytoplasm. Small numbers of benign lymphocytes and eosinophils may be present. Thymic remnants may be seen, recognition being facilitated by immunohistochemistry.

Rarely there is an association with Hodgkin lymphoma, nodular sclerosis, so called "composite lymphoma".

Immunohistochemistry (with nodal and extranodal DLBCL lymphoma for comparison)

 

mediastinal large B-cell lymphoma

nodal DLBCL

extranodal DLBCL

 

CD3

negative2, 0/243

0/523

0/483

 

CD5

negative, 0/243

5/52

2/483

CD10

6/191, 2/243

20/52

12/483

CD11a

often positive

 

 

CD19

positive

 

 

CD20

positive, 24/243

 52/523

47/483

CD21

usually negative

 

 

CD23

often positive, 17/243

8/523

4/483

CD30

often present but weak, 20/243

14/523

7/483

CD45

positive

 

 

CD79a

positive

 

 

SIg

6/191

 

 

bcl-2

positive2, 15/243

28/523

21/483

bcl-6

19/19 (nuclear)1, 14/243

43/523

21/483

       

 

Differential diagnosis

Prognosis

Mediastinal large B-cell lymphoma often responds well to aggressive therapy2. Prognosis depends on the stage of the disease, but 80% of patients achive complete remission and 60% are alive at 5 years2..

References

World Health Organization Classification of Tumours, Tumours of the haematopoietic and lymphoid tissues, IARC Press 2001.

1de Leval, L., Ferry, J. A., Falini, B., Shipp, M., Harris, N. L. Expression of bcl-6 and CD10 in primary mediastinal large B-cell lymphoma: evidence for derivation from germinal center B cells? Am J Surg Path 2001;25:1277-1282.

2Pileri, S.A., Dirnhofer, S., Went, P., Ascani, S., Sabattini, E., Marafioti, T., Tzankov, A., Leoncini, L., Falini, B. and Zinzani, P.L. Diffuse large B-cell lymphoma: one or more entities? Present controversies and possible tools for its subclassification. Histopathology 2002;41:482-509.

3Calaminici, M., K. Piper, et al. (2004). "CD23 expression in mediastinal large B-cell lymphomas." Histopathology 45(6): 619-24.

This page last revised 17.12.2004.