Original ArticleB-Cell Specific Activation Protein Encoded by the PAX-5 Gene Is Commonly Expressed in Merkel Cell Carcinoma and Small Cell CarcinomasDong, Henry Y MD, PhD; Liu, Wei MD; Cohen, Patti MD; Mahle, Christina E MD; Zhang, Weisu MD Author Information From Genzyme Genetics/IMPATH, New York, NY. Reprints: Henry Y. Dong, MD, PhD, Genzyme Genetics/IMPATH, 521 West 57th Street, New York, NY 10019 (e-mail: [email protected]). The American Journal of Surgical Pathology: May 2005 - Volume 29 - Issue 5 - p 687-692 doi: 10.1097/01.pas.0000155162.33044.4f Buy Metrics Abstract PAX-5 is a B cell specific transcription factor crucial for B cell ontogeny and has been detected in most of human B-cell lymphomas. In mouse, PAX-5 is also highly expressed in the central nervous system under tight temporal and spatial controls during embryogenesis. In humans, however, detection of PAX-5 in cells other than B lymphocytes has rarely been reported. We have encountered cases of Merkel cell carcinoma expressing PAX-5 during our routine evaluation of lymphoma. Because Merkel cell carcinoma is a small blue round cell tumor constantly in the differential diagnosis of lymphoma, we expanded our study in an effort to determine if PAX-5 is significantly expressed in neuroendocrine tumors. Based on our immunohistochemistry results using a monoclonal anti-PAX5 antibody with paraffin-embedded tissue sections, we report herein that PAX-5 was detected in 29 of 31 (93.5%) of Merkel cell carcinoma and 22 of 30 (73.3%) of small cell carcinoma, but in none of 17 cases of carcinoid tumor. Furthermore, the staining intensity of PAX-5 in Merkel cell carcinoma was frequently comparable with that in most B-cell lymphomas. We conclude that expression of PAX-5 is not confined to the B cell lineage and is frequently associated with neuroendocrine carcinomas. © 2005 Lippincott Williams & Wilkins, Inc.
