• All IHC stains will include a positive control tissue

• Atypical teratoid/rhabdoid tumor (ATRT) are highly aggressive brain tumors of infancy and early childhood that respond poorly to therapy. While the diagnosis is suggested by the presence of epithelioid cells with round nuclei, prominent nucleoli and frequent mitoses, overlap exists between ATRT and other embryonal brain tumors. The great majority of ATRT show loss of expression of INI-1 (also known as SMARCB1, hSNF5), a member of the SWI/SNF chromatin remodeling complex. Both germline and acquired mutations of INI1 are observed ¹
• Loss of INI-1 expression has also been observed in the majority of epithelioid sarcoma, and in some epithelioid MPNST and myoepithelial carcinoma ²
• Familial schwannomatosis cases may also be secondary to INI1mutation, and schwannomas in this setting will contain a mosaic pattern of INI1 loss by immunohistochemistry ^2,3
• Although numbers are limited, medullary carcinoma of the kidney also appears to show loss of INI-1 ²
• Very rare cases of ATRT are attributed to post-transcriptional mechanisms of INI-1 loss, but these appear to also be detected by INI-1 immunohistochemistry ⁴
• Very rare cases of ATRT with retained INI-1 and un-mutated INI1 are described, and have been attributed to mutation and inactivation of SMARCA4 (BRG1) ⁵

Submit a formalin-fixed, paraffin-embedded tissue

Formalin-fixed, paraffin-embedded (FFPE) tissue block

FFPE tissue section mounted on a charged, unstained slide

Ambient (preferred)

• Unlabeled/mislabeled block
• Insufficient tissue
• Slides broken beyond repair

Immunohistochemical staining and microscopic examination

If requested, an interpretive report will be provided

Specifications

• Recognizes a component of the hSWI/SNF chromatin remodeling complex that is lost in the great majority of atypical teratoid/rhabdoid tumors (ATRT)
• External controls consist of an example of ATRT, which demonstrates loss of staining, and an example of medulloblastoma, which shows retained staining. Internal controls are also present in every case, and consist of background benign tissues including endothelium within the tumor

Staining pattern

• Nuclear staining in normal tissues and tumors other than ATRT (and a few other rare tumors; see below)
• Loss of staining is noted in ATRT cells
• Photomicrograph below shows typical ATRT staining pattern. Note the preservation of staining within admixed endothelium and benign cells: this serves as a positive internal control

References

1. Biegel JA, Tan L, Zhang F, Wainwright L, Russo P, Rorke LB. Alterations of the hSNF5/INI1 gene in central nervous system atypical teratoid/rhabdoid tumors and renal and extrarenal rhabdoid tumors. Clin Cancer Res 2002 Nov;8(11):3461-3467.
2. Hollmann TJ, Hornick JL. INI1-deficient tumors: diagnostic features and molecular genetics. Am J Surg Pathol 2011 Oct;35(10):e47-63.
3. Patil S, Perry A, Maccollin M, Dong S, Betensky RA, Yeh TH, et al. Immunohistochemical analysis supports a role for INI1/SMARCB1 in hereditary forms of schwannomas, but not in solitary, sporadic schwannomas. Brain Pathol 2008 Oct;18(4):517-519.
4. Tsai CY, Wong TT, Lee YH, Chao ME, Lin SC, Liu DJ, et al. Intact INI1 gene region with paradoxical loss of protein expression in AT/RT: implications for a possible novel mechanism associated with absence of INI1 protein immunoreactivity. Am J Surg Pathol 2012 Jan;36(1):128-133.
5. Hasselblatt M, Gesk S, Oyen F, Rossi S, Viscardi E, Giangaspero F, et al. Nonsense mutation and inactivation of SMARCA4 (BRG1) in an atypical teratoid/rhabdoid tumor showing retained SMARCB1 (INI1) expression. Am J Surg Pathol 2011 Jun;35(6):933-935.