PAX5 is a B cell specific transcription factor crucial for B cell ontogeny and has been detected in most of human B-cell lymphomas.

PAX5 gene encodes a B-cell-specific activator protein (BSAP) that binds to promoters of the CD19 gene, B cell-specific tyrosine kinase gene BLK (MIM.191305), and to regulatory regions of the immunoglobulin heavy chain locus, including sequences implicated in Ig class switching.

In mouse, PAX5 is also highly expressed in the central nervous system under tight temporal and spatial controls during embryogenesis. In humans, however, detection of PAX5 in cells other than B lymphocytes has rarely been reported.

Expression in tumors

 B-cell lymphomas
 Merkel cell carcinoma (93.5%) (#15832095#)
 neuroendocrine small cell carcinoma (73.3%) (#15832095#)

Pathology

 PAX5/IGH rearrangement by t(9;14)(p13;q32) (9p13 and 14q32) in 50% of lymphoplasmacytic lymphoma

References

 Dong HY, Liu W, Cohen P, Mahle CE, Zhang W. B-Cell Specific Activation Protein Encoded by the PAX-5 Gene Is Commonly Expressed in Merkel Cell Carcinoma and Small Cell Carcinomas. Am J Surg Pathol. 2005 May;29(5):687-92. PMID: #15832095#