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Diagnostic Uses of Pax5 Immunohistochemistry

Feldman, Andrew L. MD; Dogan, Ahmet MD, PhD

Advances in Anatomic Pathology: September 2007 - Volume 14 - Issue 5 - p 323-334
doi: 10.1097/PAP.0b013e3180ca8a49
New Antibodies

Pax5, or B-cell–specific activator protein, is a nuclear protein in the paired-box containing (PAX) family of transcription factors involved in control of organ development and tissue differentiation. Pax5 is mostly expressed in B lymphocytes and B-cell lymphomas, although recent data have shown expression in the developing central nervous system, some neuroendocrine tumors, and occasional myeloid leukemias. Pax5 immunohistochemistry shows robust nuclear staining, and has become a valuable tool in the diagnosis and subclassification of lymphomas. Pax5 staining is positive in most Hodgkin and B-cell non-Hodgkin lymphomas, and also precursor B-cell lymphoblastic neoplasms. Plasma cell neoplasms, multiple myeloma, and plasmablastic lymphomas typically are negative. T-cell lymphomas are, to date, consistently negative. Recently, Pax5 expression has been described in the majority of small cell carcinomas and Merkel cell carcinomas. Rare cases of Pax5 expression in other carcinomas have been reported. With these exceptions, Pax5 immunohistochemistry is fairly specific for B-cell lineage and is a valuable addition to the armamentarium of markers available for lymphoma subtyping.

Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN

Reprints: Andrew L. Feldman, MD, Department of Laboratory Medicine and Pathology, Mayo Clinic, Hilton 11-52D, 200 1st St SW, Rochester, MN 55905 (e-mail:

Received for publication December 28, 2006; accepted May 1, 2007

© 2007 Lippincott Williams & Wilkins, Inc.