The Diagnostic Utility of PAX8 for Neuroendocrine Tumors: An Immunohistochemical Reappraisal.

PAX8 is a transcription factor crucial for the development of the kidneys, thyroid glands, and Mullerian system. It is commonly expressed by epithelial tumors from these organs. Recently, the diagnostic utility of PAX8 has been expanded to pancreatic neuroendocrine tumors (NETs). However, PAX8 is not expressed by pancreatic islets during organogenesis. The potential cross-reactivity of polyclonal PAX8 antibody to other PAX family members makes it essential that related findings need to be validated. In this study, we used 4 antibodies (1 polyclonal and 3 monoclonal) on 115 NETs from various organs (pancreas, n=20; thymus, n=16; cervix, n=27; parathyroid, n=7; and thyroid, lung, ileum, stomach, duodenum, appendix, rectum, ovary, and skin, each n=5) to test the utility of PAX8 as a differential diagnosis marker of NETs. Our results showed that NETs from a large variety of organs except for lung and ileum could be immunoreactive to the 2 less specific antibodies that have been observed to cross-react with other PAX proteins (Proteintech polyclonal and Cell Marque MRQ50). However, all NETs were immunonegative for the other 2 monoclonal antibodies specific for the less conserved C-terminal portion of PAX8 (Abcam PAX8R1 and Biocare BC12). We concluded that PAX8 may provide help in the differential diagnosis of NETs in certain specific contexts but the antibody used and the clinical information must be considered.