Table of Contents Author Guidelines Submit a Manuscript
Case Reports in Pathology
Volume 2016, Article ID 3291549, 5 pages
http://dx.doi.org/10.1155/2016/3291549
Case Report

Undifferentiated Malignant Neoplasm Involving Parotid and Thyroid: Sampling and PAX8 Cross-Reactivity Can Obscure the Diagnosis of Lymphoma

Department of Pathology, University of Tennessee Graduate School of Medicine, Knoxville, TN, USA

Received 29 July 2016; Revised 10 November 2016; Accepted 28 November 2016

Academic Editor: Lubos Holubec

Copyright © 2016 Elizabeth W. Hubbard et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Poorly differentiated malignant neoplasia arising within the head and neck region may originate from diverse sources. We report a case of a cytologically undifferentiated malignant neoplasm clinically presenting as masses involving thyroid and parotid. Although PAX8 was immunoreactive and thus worrisome for anaplastic thyroid carcinoma, the tumor was eventually proven to represent PAX5 positive diffuse large B-cell lymphoma expressing cross-reactivity with polyclonal PAX8 antibody. Cross-reactivity between commercially available polyclonal PAX8 and PAX5 immunostains has been described in the literature but is not widely known, and it is a potential pitfall for making a misdiagnosis. This distinction can have importance in selection of subsequent clinical therapy and should be considered in choice of immunohistochemical stains for diagnostic purposes.