Stains & CD markers
INI1 / SMARCB1


Last author update: 1 June 2022
Last staff update: 1 June 2022

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PubMed Search: INI1 / SMARCB1

Felix K.F. Kommoss, M.D.
Christian M. Schürch, M.D., Ph.D.
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Cite this page: Kommoss FKF, Schürch CM. INI1 / SMARCB1. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/stainsini1.html. Accessed July 3rd, 2022.
Definition / general
  • SMARCB1 (switch / sucrose non fermentable [SWI / SNF] related, matrix associated, actin dependent regulator of chromatin subfamily B member 1) is located on chromosome 22q11.2 and encodes a core subunit of the adenosine triphosphate (ATP) dependent SWI / SNF chromatin remodeling complex, which is actively involved in the regulation of gene expression
Essential features
  • SMARCB1 is a core subunit of the SWI / SNF chromatin remodeling complex
  • SMARCB1 is considered a bona fide tumor suppressor
  • Germline SMARCB1 mutations are associated with rhabdoid tumor predisposition syndrome 1 and familial schwannomatosis
  • Loss of SMARCB1 expression is identified in a variety of rhabdoid and nonrhabdoid neoplasms of the CNS, soft tissue and parenchymal / visceral organs
Terminology
  • SMARCB1 (SWI / SNF related, matrix associated, actin dependent regulator of chromatin subfamily B member 1), INI1 (integrase interactor 1), BAF47, hSNF5
Pathophysiology
  • Core subunit of the ATP dependent SWI / SNF chromatin remodeling complex involved in transcriptional activation and repression through chromatin remodeling
  • Bona fide tumor suppressor interacting with other cancer associated pathways (e.g., WNT signaling pathway and hedgehog signaling pathway) (Nat Med 2010;16:1429)
  • Initially discovered as a protein that binds HIV integrase (Science 1994;266:2002)
Clinical features
Interpretation
  • Nuclear stain
Uses by pathologists
Prognostic factors
  • Currently unknown
Microscopic (histologic) images

Contributed by Andreas von Deimling, M.D. and Thomas Mentzel, M.D.

Atypical teratoid / rhabdoid tumor

Epithelioid sarcoma, proximal type

Positive staining - normal
  • SMARCB1 is ubiquitously expressed in the nuclei of all normal human cells
Positive staining - disease
  • Most tumors show nuclear expression of SMARCB1
  • Synovial sarcoma may show reduced expression of SMARCB1 (Mod Pathol 2010;23:981)
Negative staining
Molecular / cytogenetics description
  • Malignant rhabdoid tumors (MRT) of kidney and soft tissue as well as CNS atypical teratoid / rhabdoid tumor (AT / RT): point and frameshift mutations, deletions or translocations involving SMARCB1 and monosomy 22 (Pediatr Blood Cancer 2011;56:7)
  • Epithelioid sarcoma: homozygous deletion of SMARCB1 can be demonstrated by FISH in most (90%) cases (Genes Chromosomes Cancer 2014;53:475)
  • Medullary renal carcinoma: translocations and heterozygous deletion of SMARCB1 in most cases (Eur Urol 2016;69:1055)
  • SMARCB1 deficient sinonasal carcinoma / adenocarcinoma: homozygous deletion of SMARCB1 can be demonstrated by FISH in most (68%) cases; heterozygous deletion or truncating mutation identified in a subset of cases (Hum Pathol 2020;104:105)
  • Poorly differentiated chordoma: homozygous deletion of SMARCB1 can be demonstrated by FISH in most (90%) cases (Acta Neuropathol 2016;132:149, Genes Chromosomes Cancer 2018;57:89)
  • Myoepithelial carcinoma of soft tissue: homozygous deletion of SMARCB1 can be demonstrated by FISH in a subset of cases (Genes Chromosomes Cancer 2014;53:475)
  • Epithelioid benign and malignant peripheral nerve sheath tumors: nonsense, frameshift and splice site mutations as well as deletions in SMARCB1 (Am J Surg Pathol 2019;43:835)
  • Dedifferentiated / undifferentiated endometrial and ovarian adenocarcinoma: nonsense and frameshift mutations in SMARCB1 can be identified in a subset of cases (Mod Pathol 2016;29:1586)
Board review style question #1
Which of the following neoplasms is associated with loss of SMARCB1 expression?

  1. Basal cell carcinoma
  2. Embryonal rhabdomyosarcoma
  3. Leiomyosarcoma
  4. Malignant rhabdoid tumor of the kidney
  5. Merkel cell carcinoma
Board review style answer #1
D. Malignant rhabdoid tumor of the kidney

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Reference: INI1 / SMARCB1
Board review style question #2

Which of the following is typically lost in CNS atypical teratoid / rhabdoid tumors (AT / RT)?

  1. BAP1
  2. CDKN2A
  3. NF1
  4. PTEN
  5. SMARCB1
Board review style answer #2
E. SMARCB1

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Reference: INI1 / SMARCB1
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