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Stains

INI1

Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 7 December 2011, last major update December 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Terminology
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● Also called hSNF5, SMARCB1, BAF47

Physiology
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● Loss of INI1 expression usually associated with deletion or mutation of the INI1 gene on 22q11.2, but not always (Am J Surg Pathol 2011 Oct 20 [Epub ahead of print])
● INI1 is a chromatin remodeling protein which represses Aurora A, required for rhabdoid tumor cell survival (Cancer Res 2011;71:3225)

Interpretation
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● Nuclear stain

Uses by Pathologists
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● Diagnosis of CNS atypical teratoid/rhabdoid tumors, renal medullary carcinoma, rhabdoid tumors
● Distinguish atypical teratoid/rhabdoid tumor (loss of INI1) from choroid plexus carcinoma (INI1+, J Neuropathol Exp Neurol 2005;64:391)

Clinical features
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● Germline INI1 mutations associated with sporadic schwannomatosis (10% of cases, BMC Neurol 2011 Jan 24;11:9), rhabdoid tumors (35%, Clin Cancer Res 2011;17:31)
● Represses basal HIV1 promoter activity (J Gen Virol 2009;90:2503)

Micro images
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Left to right: renal medullary carcinomas, renal rhabdoid tumors, renal cell carcinomas with rhabdoid features

   
CNS tumors: left - atypical teratoid/rhabdoid tumor; right - anaplastic oligodendroglioma

   
Renal tumors: left - malignant rhabdoid tumor; right - Wilm's tumor


Orbital rhaboid tumor

       
Composite rhabdoid tumors

       
Synovial sarcoma (left/middle) with rhaboid features shows reduced expression, compared to mimics, which show full expression

Positive staining - normal
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● Most normal cells

Positive staining - disease
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● Composite rhabdoid tumors, including rhabdoid meningioma (Mod Pathol 2005;18:951), synovial sarcoma (but reduced levels in 65%, Mod Pathol 2010;23:981)
● Renal cell carcinoma or urothelial carcinoma, including those with histological rhabdoid features

Negative staining
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● Loss of INI1 expression found in CNS atypical teratoid/rhabdoid tumor (Am J Surg Pathol 2004;28:644), epithelioid MPNST (50%), epithelioid sarcoma (Am J Surg Pathol 2009;33:542, Am J Clin Pathol 2009;131:222)
● Also extraskeletal myxoid chondrosarcomas (15%, Am J Surg Pathol 2008;32:1168), myoepithelial carcinoma (occasional), renal medullary carcinoma (Mod Pathol 2008;21:647), renal rhabdoid tumor (pediatric and adult)

End of Stains > INI1

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