Thursday, June 27th, 9pm EST

Article discussed: Diagnostic Algorithm of Common Mature B-Cell Lymphomas by Immunohistochemistry

Authors: Huan-You Wang, MD, PhD; Youli Zu, MD, PhD

Open access at: https://doi.org/10.5858/arpa.2016-0521-RA

Summary prepared by: Abdullah Alswied, MBBS, MRes, PhD (@AlswiedPath)

 

Journal Club summary:

Study Background: Immunohistochemical profiles of different types of mature B-cell lymphomas, including plasma cell neoplasms exhibit distinct profiles, which enable them to be correctly diagnosed. However, except for rare examples of lymphoma, immunohistochemical profiles of mature B-cell lymphomas overlap and lack specificity.

Objectives:

Three main objectives of the paper:

1- systemically review immunohistochemical features associated with commonly encountered mature B-cell lymphomas based on the presence or absence of CD5 and CD10.

2- review the immunophenotypic profile of plasma cells derived from plasma cell myelomas and B-cell lymphomas.

3- review a group of rare, aggressive B-cell lymphomas with antigen expression features of plasma cells

Discussion:

First objective:

Systemically review immunohistochemical features associated with commonly encountered mature B-cell lymphomas based on the presence or absence of CD5 and CD10 (Summarized in the table below).

A- CD5+/CD10- B-cell lymphomas:

– Two classic examples, small lymphocytic lymphoma (SLL) and mantle cell lymphoma (MCL).

– Lymphoplasmacytic lymphoma (LPL) CD5 expression is anecdotal by IHC.

– Marginal zone B-cell lymphoma (MZBCL) CD5 expression is variable based on its morphologic type.

– Diffuse large B-cell lymphomas (DLBCLs) expression of CD5 is seen in 10% of the cases. It is interesting to note that these lymphomas (CD5+) have higher rates of BCL2 expression.

B- CD10+/CD5- B-cell lymphomas:

– Follicular lymphoma (FL) and Burkitt lymphoma (BL) are the 2-prototypical B-cell lymphomas expressing CD10. The authors recommend a minimal IHC panel for FL should include BCL2, CD3, CD10, and CD20; however, ideally, BCL6, CD5, and CD21 should be included as well.

– Hairy cell leukemia (HCL) and MCL can occasionally be positive for CD10. The authors noted that CD10+ expression in MCL is related to a distinct GC signature rather than an immunophenotypical aberrancy.

– DLBCL: Although approximately 90% of DLBCLs NOS are negative for CD5 and10% to 40% of de novo DLBCLs NOS are positive for CD10.

C- CD5-/CD10- B-cell lymphomas:

– The prototypic CD5-/CD10- mature B-cell lymphomas of small cell size are MZBCL, LPL, and HCL. Most DLBCLs NOS are also negative for both CD5 and CD10.

– In this section, the authors mainly focused on MALT lymphoma and recommended the addition of CD43, lamda and kappa light chains to the panel of IHC.

– Lymphoplasmacytic lymphoma is diagnosed by exclusion, and at times, MZBCL and LPL cannot be distinguished based on morphologic and immunophenotypic features alone.

– The monotypic PCs derived from B-cell lymphoma have a similar immunophenotype to B cells and differ from those of PC myeloma.

– Hairy cell leukemia is positive for all common B-cell antigens with characteristic expression of annexin A1.

– After excluding CD5+ and/or CD10+ DLBCL NOS, approximately 50% to 70% of de novo DLBCLs NOS are negative for both CD5 and CD10.

Second Objective:

Review the immunophenotypic profile of plasma cells derived from plasma cell myelomas and B-cell lymphomas.

– CD38 and CD138 can not differentiate neoplastic PCs derived from PCM from PCs derived from B-cell lymphomas.

– By flow cytometry, CD19 provided the best criterion for distinguishing between these 2 types of neoplastic PCs as neoplastic PCs from B-cell lymphomas are positive for CD19 and are almost always negative in neoplastic PCs from PCM.

– The combination of BCL1, CD19, CD45, CD56, and CD117 is sufficient to distinguish PCs derived from PCMs and/or plasmacytomas from B-cell lymphomas, even in cases in which there is exuberant plasmacytic differentiation

Third objective:

Review a group of rare, aggressive B-cell lymphomas with antigen expression features of plasma cells.

– Lymphomas discussed in this sections include, plasmablastic PCM; plasmablastic lymphoma (PBL); primary effusion lymphoma (PEL); large B-cell lymphoma arising in HHV8-associated multicentric Castleman disease, and ALK⁺ large B-cell lymphoma

– CD38, CD138, and MUM1 are positive in all cases of plasmablastic PCM, PBL, and PEL.

– Plasmablastic PCM and PBL cannot be separated from each other based on an IHC panel that includes CD45, CD79a, CD56, and PAX5 and the authors recommend the utilizations of CD19.

– The authors provided no recommended panel for PEL other than utilizing the clinical history and HHV8 immunostain.

– ALK+ large B-cell lymphoma is typically negative for most of the common B-cell antigens but positive for PC markers such as CD138, VS38, EMA, and MUM1.

Conclusion:

1- the presence or absence of CD5 and CD10 expression should be included in the initial immunohistochemistry screening panel for mature B-cell lymphomas, appropriate and judicial use of other B-cell antigens is necessary to ensure correct diagnoses.

2- Plasma cells from plasma cell neoplasias and B-cell lymphomas exhibit overlapping but relatively distinct immunophenotypes; thus, a panel of immunohistochemical markers (CD19, CD45, CD56, and CD117) can be employed for their proper identification.

3- CD138 staining results are almost always positive in a group of aggressive B-cell lymphomas with plasmablastic features, including plasmablastic plasma cell myeloma, plasmablastic lymphoma, andALK-1fllarge B-cell lymphoma.

Some Highlights from the Evening:

Thank you so much for attending and for reading this summary. We are so excited to plan yet another journal club for next month. Stay tuned.

Kind regards!

DermpathJC