Stains
MUM1 / IRF4

Author: Nat Pernick, M.D. (see Authors page)

Revised: 11 November 2015, last major update September 2012

Copyright: (c) 2002-2015, PathologyOutlines.com, Inc.

PubMed Search: MUM1 [title]

Definition / General
  • Transcriptional factor (MUM1 / IRF4, MUltiple Myeloma 1 / Interferon Regulatory Factor 4 protein) expressed in final step of intragerminal center B cell differentiation and in post-germinal center (late centrocyte) B cells (Blood 2000;95:2084, Appl Immunohistochem Mol Morphol 2010;18:301)
  • Antigen stimulated B cells with the capacity to differentiate toward plasma cells express MUM1 / IRF4
  • Has critical role in lymphoid development and in regulating immune response (Proc Natl Acad Sci USA 2012;109:8664)
  • Usually mutually exclusive with BCL6 in nonneoplastic tissue: germinal center cells are MUM1- BCL6+ CD10+ and post-germinal (non germinal center) cells are MUM1+ BCL6- CD10-
    • Mantle cells are MUM1- BCL6- CD10-
  • Note: in botany, refers to mucilage modified mutant of seed coat epidermal cells
Uses by Pathologists
  • Nuclear stain
  • Helps divide diffuse large B cell lymphomas into germinal center (MUM1-) and non-germinal center (post-germinal center or activated B-like, MUM1+) phenotypes
  • Germinal center phenotypes have superior outcomes (Am J Surg Pathol 2009;33:1815)
  • FISH for IRF4 favors cutaneous anaplastic large cell lymphoma versus other cutaneous T cell lymphoproliferative disorders (Mod Pathol 2011;24:596)
  • As part of panel, may help differentiate nodular lymphocyte predominant Hodgkin lymphoma (MUM1 / IRF4 negative) from classical Hodgkin lymphoma (positive, Rom J Morphol Embryol 2011;52:69)
  • Helps differentiate double hit lymphomas (MUM1+ in 45%) from Burkitt and diffuse large B cell lymphoma (usually MUM1- if germinal center phenotype, Am J Surg Pathol 2010;34:327)
Micro Images

Images hosted on Other servers:

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Normal lymph node

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Lymphoma, Burkitt, MUM1+

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Lymphoma, anaplastic large cell

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Non-GCB of DLBCL

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MUM1 expression

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MUM1+, Fig.F

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MUM1+, ALK-DLBCL

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MUM1+, Fig.C

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Strong MUMI, Fig.E

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Double hit lymphoma

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Mantle cell lymphoma

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Lymphoma, plasmablastic

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Lymphoma, primary effusion, HIV+

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Polymorphic PTLD, EBV+



Positive Staining - Normal
  • B cells (some), plasma cells
Positive Staining - Disease
Negative Staining
  • T-ALL
Molecular / Cytogenetics Description
  • FISH detection of MUM1 / IRF4 translocation (DUSP22-IRF4) favors cutaneous anaplastic large cell lymphoma (Mod Pathol 2011;24:596)
  • FISH detection of IG/IRF4 fusion detects lymphomas associated with younger patient age and favorable outcome (Blood 2011;118:139)
  • t(6;14)(p25;q32), causing MUM1/IRF4-IgH, present in 20% of myeloma (Leukemia 1999;13:1812)
Molecular / Cytogenetics Images
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IRF4 / MUM1 FISH abnormalities