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Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 26 November 2011, last major update November 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.


● Also called Paired box 8; discovered in 1990 (Development 1990;110:643)
● Paired domains are composed of two helix-turn-helix subdomains - the N-terminal subdomain and the C-terminal subdomain, both of which can bind DNA independently (Cell 1995;80:639)
● Structurally similar to PAX2 and PAX5


● Gene is at 2p13 (NCBI-Gene)
● Transcription factor critical for development of eye, thyroid, urinary and reproductive organs
● Associated with tumors of thyroid gland, kidney/upper urinary tract and Müllerian system
● Mutations associated with congenital hypothyroidism and hypoplasia (J Clin Endocrinol Metab 2001;86:3962, J Clin Endocrinol Metab 2001;86:234)
● PAX8-PPARgamma rearrangement in follicular thyroid carcinoma (53%, Am J Surg Pathol 2002;26:1016), follicular adenoma (8%) and follicular variant of papillary thyroid carcinoma (38%, J Clin Endocrinol Metab 2006;91:213)


● Nuclear staining
● Actually negative in B cell lymphomas, but reported positive due to cross-reactivity between the N-terminal regions of PAX8 and PAX5, due to the high sequence homology of these two regions (Mod Pathol 2011 Oct 28 [Epub ahead of print])

Uses by Pathologists

● (1) Differentiate PAX8+ primary or metastatic tumors (kidney, Mullerian [but not mucinous, Am J Surg Pathol 2011;35:1837], thymic, thyroid) from PAX8- tumors (adrenal, breast, GI [most], lung, prostate, Am J Surg Pathol 2011;35:816)
● (2) Differentiate prostatic mesonephric remnant hyperplasia (PAX8+) from prostatic adenocarcinoma (PAX8-, Am J Surg Pathol 2011;35:1054)
● (3) Differentiate metastatic clear cell renal cell carcinoma (PAX2+ or PAX8+/inhibinA neg) from hemangioblastoma (PAX2-, PAX8-, inhibin A+, Am J Surg Pathol 2011;35:262)
● (4) Differentiate endosalpingiosis in axillary lymph nodes (PAX8+/WT1+) from metastatic breast carcinoma (PAX8-, WT1-, Am J Surg Pathol 2010;34:1211)
● (5) Differentiate renal collecting duct carcinoma (PAX8+/p63-) from urothelial carcinoma of upper urinary tract (PAX8-/p63+, Am J Surg Pathol 2010;34:965)
● (6) Differentiate thyroid anaplastic carcinoma (PAX8+) from head and neck squamous cell carcinoma (PAX8-, Hum Pathol 2011;42:1873)
● (7) Determine primary site of invasive micropapillary carcinomas as part of panel (Am J Surg Pathol 2009;33:1037)
● (8) Marker of nephrogenic adenoma
● (9) Determine renal tubular origin of various disease processes (Am J Surg Pathol 2011;35:1264)

Micro images

Normal adult kidney

PAX2 and PAX8 in normal kidney and kidney tumors

Renal carcinomas and oncocytoma

Thyroid carcinomas

Urothelial carcinomas of the renal pelvis

Positive staining - normal

● Epithelium of endocervix, endometrium, fallopian tubes, kidney (glomerular parietal epithelial cells, renal collecting ductal cells, atrophic renal tubular epithelial cells, Mod Pathol 2011;24:751), thyroid; ovarian inclusion cysts, pancreatic islet cells
● Epithelium of male genital tract from rete testis to ejaculatory duct, but not prostate

Positive staining - disease

● Endometrial polyp, endometriosis, endosalpingiosis, paratubal cyst, prostatic mesonephric remnant hyperplasia
● Bladder clear cell adenocarcinoma, endometrial adenocarcinoma
● Ovarian carcinoma, except mucinous types (Am J Surg Pathol 2008;32:1566)
● Renal cell carcinoma (90%, Mod Pathol 2009;22:1218), including Xp11 translocation subtype (Am J Surg Pathol 2010;34:1295), renal oncocytoma (81%), nephrogenic adenoma (Am J Surg Pathol 2008;32:1380), nephroblastoma, renal cell carcinoma
● Seminoma, thymic carcinoma, thymoma types A and B (Am J Surg Pathol 2011;35:1305)
● Thyroid anaplastic carcinoma (Mod Pathol 2008;21:192) and other thyroid tumors (91%, Am J Surg Pathol 2011;35:816)
● Carcinoid tumors: gastric/duodenal (100%), rectal (85%), appendix (21%), gastric (20%), but not ileal, lung (Am J Surg Pathol 2010;34:723) or renal (Hum Pathol 2011;42:1554)
● Neuroendocrine tumors: duodenal (75%), pancreas (67%, Am J Surg Pathol 2010;34:723), rectal (29%), gastric (10%), appendiceal (9%), but not ileal or lung (Mod Pathol 2011;24:412)

Negative staining

● Normal epithelium of bladder, lung, parathyroid (Am J Surg Pathol 2011;35:757) and prostate
● Normal testis: seminiferous tubules, interstitium
● Carcinomas: adrenal gland, bile duct, breast (Am J Clin Pathol 2011;136:428), gastric, GE junction, lung, pancreas, prostate, urothelial (also urothelial adenocarcinoma and squamous carcinoma, Appl Immunohistochem Mol Morphol 2011;19:293)
● Adenomatoid tumor, Leydig and Sertoli cell tumors, germ cell tumors (Am J Surg Pathol 2011;35:1473), mesothelioma (Am J Surg Pathol 2010;34:627)
● B cells and B cell lymphomas (reported positive due to cross reactivity with PAX5 due to high sequence homology)

End of Stains > PAX8

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