Loss Of INI1 Expression Research Articles

Hepatic adenosquamous carcinoma with sarcomatous transformation: a case report and review of the literature.

Adenosquamous carcinoma (ASC) with the presence of a sarcomatous component is exceptionally uncommon in intrahepatic cholangiocarcinoma (iCCA). We report a case of hepatic ASC with rhabdoid transformation, one variation of sarcomatous change. A 72-year-old man was admitted to our hospital after being diagnosed with a 45mm-diameter neoplastic lesion in the right hepatic duct on abdominal computed tomography. Laboratory findings showed increases in AST, ALT, ALP, gamma-GT, CA19-9 and DUPAN-II. The patient then underwent an extended right hepatectomy. Histopathologically, the tumor was composed of an ASC component within an abundant fibrous stroma and a sarcomatoid carcinoma component. By immunohistochemistry, keratin 7 and keratin 19 were expressed by all tumor cells. Expression of keratin 5/6, p40 and p63 was restricted to the squamous component. The sarcomatoid component was immunoreactive for vimentin with no loss of INI1 expression. This component also showed a loss of membranous E-cadherin expression and a reduction of membranous β-catenin expression. Staining for desmin, myoglobin and HepPar1 was negative in any tumor cells. The patient died of liver failure 3months after surgery. This report aims to provide a better understanding of the clinicopathological characteristics and disease progression of the rare variants of iCCA to aid diagnosis and treatment.

ATRT-08. ATYPICAL TERATOID RHABDOID TUMOR IN AN ADULT PATIENT WITH DOWN SYNDROME

Abstract BACKGROUND Atypical teratoid/rhabdoid tumor (ATRT) is a malignant, highly aggressive embryonal tumor of the central nervous system. Long-term survival remains dismal despite aggressive multimodal therapy, including a maximal safe surgical resection and intensive systemic chemotherapy +/- radiation therapy. While these tumors typically present in infancy or early childhood, there are scattered case reports of adult-onset ATRT. Making prognostic conclusions or therapeutic decisions for this older patient population remains challenging due to the paucity of these reports. CASE REPORT A 25-year-old female with Down syndrome presented with nausea, vomiting, dysphagia, and facial droop and was found to have an avidly enhancing, left cerebellopontine angle mass. There was initial clinical suspicion for leukemic chloroma given the patient’s Down syndrome status and known association with higher rates of hematologic malignancy concurrent with a dramatic scarcity of solid tumors in the Down syndrome population. However, histology demonstrated sheets of high-grade rhabdoid cells with loss of INI1 expression, pathognomonic for ATRT. Further sequencing defined a frameshift mutation in SMARCB1 (p.C298), and methylation profiling matched with high confidence to the MYC subclass of ATRT. The patient was treated with subtotal surgical resection and focal proton radiation, followed by chemotherapy on a modified regimen based on the Children’s Oncology Group protocol, ACNS0333. Systemic methotrexate and all consolidative high-dose chemotherapy with stem cell rescue were omitted due to concern for heightened risk of treatment-related toxicity. The patient remains alive and clinically asymptomatic 19 months from diagnosis. CONCLUSION This report represents the first known case of ATRT in an adult patient with Down syndrome, offering unique mechanistic insight into the tumorigenesis of ATRT. Adult ATRT is a rare entity without standardized treatment or established prognostic understanding. Further studies are needed to define an appropriate risk-adapted therapeutic approach for this patient population.

Elusive and Aggressive: Unraveling SMARCB1/INI1-Deficient Undifferentiated Carcinoma With Rhabdoid Features Arising From the Colon: A Case Report and Comprehensive Literature Review.

Undifferentiated carcinomas are highly aggressive tumors with a dismal prognosis. A subset of these tumors has been associated with inactivation or mutations of the Switch/Sucrose Nonfermenting (SWI/SNF) remodeling complex. Our understanding of the relationship between the clinicopathological features and molecular profiling of SWI/SNF-deficient undifferentiated carcinoma is still evolving due to its rarity. We herein present a rare tumor of undifferentiated carcinoma with SMARCB1/INI1 deficiency arising from the colon. The histology revealed a tumor composed of sheets of discohesive, high-grade epithelioid cells with rhabdoid morphology along with anaplastic giant cells. Additionally, there was a significant infiltration of inflammatory cells in the background. Immunohistochemical (IHC) analysis supported the diagnosis of carcinoma with loss of INI1 expression, the tumor was mismatch repair protein proficient. Molecular analysis demonstrated an oncogenic KRAS mutation (p.G12D), whereas it was wild-type BRAF, and wild-type NRAS. The diagnosis of SWI/SNF-deficient undifferentiated carcinoma can be challenging. Correlation with clinical findings, in conjunction with IHC work-up and molecular analysis, is of utmost importance to arrive at the appropriate diagnosis and exclude potential mimics.

ATRT-14. Malignant rhabdoid tumors of cranial nerves – ATRT or extracranial rhabdoid tumor?

Abstract INTRODUCTION: Malignant rhabdoid tumors (MRT) are highly aggressive neoplasias mostly affecting young children. They are classified as rhabdoid tumors of the central nervous system (ATRT, atypical teratoid rhabdoid tumor), rhabdoid tumors of the kidney (RTK) or extracranial rhabdoid tumors arising from any soft tissue outside the central nervous system (eMRT, extracranial extrarenal MRT). We report a series of four MRTs with cranial nerve involvement. METHODS: Patients were identified from a cohort of 132 patients with MRT (2017 – 2021), as part of the European Rhabdoid Registry (EU-RHAB). Diagnosis of MRT was confirmed immunohistochemically with loss of INI1 expression. Details regarding symptoms at first presentation, diagnostic staging, genetic findings, therapy and the course of disease are reported. REPORT OF CASES/RESULTS: The series contains two MRT affecting the trigeminal nerve and two cases with third cranial nerve involvement. They were two female and two male patients with a median age of 4.7 years (1-159 months) at diagnosis. Location of the main tumor mass differed between being located intra- and extracerebrally. Metastases at diagnosis occurred in one patient, a germ-line mutation in SMARCB1 was present in two patients. Two patients received therapy according to EU-RHAB recommendations with an incomplete resection, conventional chemotherapy enhanced by intraventricular methotrexate and radiotherapy. Both patients are currently alive with no signs of progression, one of them bearing a germ-line mutation. Two patients received palliative treatment after surgery due to rapid progression. Median overall survival was 17.3 (1.4-53.1) months. CONCLUSION: MRT of the cranial nerves affect the peripheral nervous system in close proximity to the brain, thus forming a unique sub-entity between ATRT and eMRT. The selected cases provide insight into the particular challenge regarding clear classification, diagnostics and therapy.

SMARCB1 (INI1)–Deficient Sinonasal Carcinoma With Yolk Sac Tumor Differentiation: Case Report and Review of the Literature

Abstract SMARCB1 (INI1)–deficient sinonasal carcinoma is a recently described primary neoplasm of the sinonasal tract that occurs infrequently and displays aggressive clinical behavior. Classic histopathologic findings of INI1-deficient sinonasal carcinoma include sheets and nests of basaloid tumors cells with a monomorphic appearance. Variable amounts of rhabdoid and glandular differentiation have been reported. Diagnosis of this lesion can be challenging because of significant morphologic and immunohistochemical overlap between other primary lesions of the sinonasal tract, including basaloid and other nonkeratinizing squamous cell carcinomas, sinonasal undifferentiated carcinoma, and the newly described BRG1-deficient sinonasal carcinoma, among others. Recently, yolk sac tumor (YST)–like differentiation has been described in multiple reports of INI1-deficient sinonasal carcinoma, which expands both the histologic spectrum of this lesion and its differential diagnosis. Although there is significant immunophenotypic overlap between primary YST and INI1-deficient sinonasal carcinoma with YST differentiation, loss of INI1 expression by immunohistochemistry is not seen in YST. INI1 immunohistochemistry is a sensitive and specific marker for identifying INI1-deficient sinonasal carcinoma, and pathologists should have a low threshold for performing this test on tumors with a myriad of histologic features.

Phase II study of nivolumab and ipilimumab in children and young adults with INI1-negative cancers.

TPS10055 Background: Several aggressive pediatric and young adult cancers are characterized by SMARCB1 inactivation resulting in loss of INI1 expression, including rhabdoid tumors, epithelioid sarcoma and undifferentiated chordoma. These malignancies are associated with a poor prognosis and few effective treatment options for relapsed or refractory disease. Prior studies and emerging data suggest INI1-negative cancers may be uniquely susceptible to treatment with immune checkpoint inhibitors: Many INI1-negative pediatric tumors express PD-L1 and are infiltrated by immune cells, and there are reports of patients with advanced INI1-negative cancers with clinical responses to immune checkpoint blockade (Forrest et al. Clinical Cancer Research, 2020). We hypothesize that INI1 loss predicts tumor response to immune checkpoint inhibition (ICI). Methods: This is an ongoing multicenter, phase II, open-label clinical trial to evaluate the activity of nivolumab and ipilimumab in patients aged 6 months to 30 years with relapsed or refractory INI1-negative cancers (NCT04416568). The study enrolls patients in 2 strata: extracranial solid tumors in Stratum 1 and intracranial solid tumors in Stratum 2. Patients treated with prior ICI are excluded. Patients are treated with intravenous (IV) nivolumab 3mg/kg plus ipilimumab 1mg/kg IV every 3 weeks for 4 cycles followed by nivolumab 3mg/kg (max dose 240mg) IV every 2 weeks for up to 1-year. The primary objective is to evaluate the objective response rate (ORR) by Response Evaluation Criteria in Solid Tumors (RECIST) for Stratum 1 and by Response Assessment in Neuro-Oncology (RANO) criteria for Stratum 2. The trial has a 2-stage design targeting a 25% or greater response rate, with each stratum assessed independently. The analysis for Stage 1 in a given Stratum will be performed after 10 patients are enrolled. If a sufficient number of responders are observed, an additional 10 patients will be enrolled at Stage 2. Secondary endpoints include progression-free survival, overall survival, and disease control rate at 12 months. Correlative aims include assessing tissue and blood biomarkers associated with treatment response. Enrollment began 14 Aug 2020 and is ongoing. Clinical trial information: NCT04416568.

SWI/SNF deficient central nervous system neoplasms

The SWItch/Sucrose Non-Fermentable (SWI/SNF) complexes are ubiquitous ATP dependent chromatin remodeling complexes that provide epigenetic regulation of gene expressions across the genome. Different combination of SWI/SNF subunits allow tissue specific regulation of critical cellular processes. The identification of SMARCB1 inactivation in pediatric malignant rhabdoid tumors provided the first example that the SWI/SNF complex may act as a tumor suppressor. It is now estimated at least 20% of all human tumors contain mutations in the subunits of the SWI/SNF complex. This review summarizes the central nervous system tumors with alterations in the SWI/SNF complex genes. Atypical teratoid/rabdoid tumor (AT/RT) is a highly aggressive embryonal tumor genetically characterized by bi-allelic inactivation of SMARCB1, and immunohistochemically shows complete absence of nuclear expression of its protein product INI1. A small subset of AT/RT show retained INI1 expression but defects in another SWI/SNF complex gene SMARCA4. Embryonal tumors with medulloblastoma, pineoblastoma, or primitive neuroectodermal morphology but loss of INI1 expression are now classified as AT/RT. Cribriform neuroepithelial tumor (CRINET) is an intra or para-ventricular tumor that has similar SMARCB1 alterations as AT/RT but generally has a benign clinical course. Besides AT/RT and CRINET, compete loss of nuclear INI1 expression has also been reported in poorly differentiated chordoma and intracranial myxoid sarcoma within the central nervous system. Families with non-truncating SMARCB1 mutations are prone to develop schwannomatosis and a range of developmental syndromes. The schwannomas in these patients usually demonstrate a mosaic INI1 staining pattern suggestive of partial residual protein function. Finally, clear cell meningioma is a WHO grade II variant meningioma characterized by bi-allelic inactivation of the SMARCE1 gene and immunohistochemically show loss of its protein product BAF57 expression in tumor cell nuclei.

Expression of WT1 in renal rhabdoid tumors: immunohistochemistry and molecular genetics

Renal rhabdoid tumor (RRT) is the most malignant and aggressive renal tumors in children. The results of immunohistochemistry show co-expression of epithelial and mesenchymal markers with total loss of INI1 expression in tumor cells. Aim. To determine the frequency of WT1 expression in RRT using three different clones and to investigate WT1 gene status. This study is supported by the Independent Ethics Committee and approved by the Academic Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. 28 patients with RRT were included in our study from a period 2006–2019. Immunohistochemical staining included Vimentin, panCK, CK19, EMA, INI1, CD34, WT1 (clones: polyclonal, WT49, 6FH2). Additionally, in order to evaluate genetic events known to be significant in the RRT pathogenesis, molecular genetic testing by multiplex ligase-dependent probe amplification (NGS) and next-generation sequencing (NGS) of customized gene panel were conducted in 15 cases with available material. All tumors had classical rhabdoid morphology with co-expression of epithelial and mesenchymal markers and total loss of INI1 expression. Two tumors were WT1-positive (WT49 and Polyclonal). 5 out of 15 tumors harbored different in length SMARCB1 gene deletions. 7 cases studied by NGS for nucleotide substitutions and small indels included 5 patients lacking SMARCB1 deletions based on the MLPA data and 2 cases of RRT with WT1 protein nuclear expression. All evaluated patients had pathogenic or likely-pathogenic genetic variants in genes encoding core subunits of SWI/ SNF chromatin remodeling complex (predominantly, SMARCB1 and SMARCA4 genes). No pathogenic variants were revealed in WT1 gene. The literature describes isolated cases of WT1 expression in RRT elements. Often, the cellular elements of a rhabdoid tumor after preoperative chemotherapy are regarded as elements of the stromal component of nephroblastoma, maturing into rhabdomyoblasts. In the presence of WT1 expression, these tumors are considered as nephroblastomas. In this study we showed that RRTs are molecularly heterogeneous tumors with aberrant immunophenotype. Thus, our experience proves the importance of an integrated approach to differential diagnosis and the need for routine use of the INI1 antibody in panels for the study of kidney tumors in children to avoid misinterpretation of morphological data.

Abstract A16: Genomic and immunologic characterization of a cohort of INI1-deficient pediatric cancers

Abstract Several aggressive cancers impacting children are characterized by alterations in the SWI/SNF complex, including rhabdoid tumors, epithelioid sarcoma, and chordoma. With recent early-phase trials showing responses to EZH2 inhibitors, it is important to understand the optimal approach to identifying INI1-deficient cancers. As tumor profiling is becoming a more routine part of clinical care, this study was designed to determine the relationship between SMARCB1 genetic variants identified by a sequencing panel test and INI1 protein expression. Beyond EZH2 inhibitors, therapeutic approaches for INI1-deficient tumors are limited. Thus, we also sought to investigate PD-L1 expression in a cohort of INI1-deficient pediatric brain and solid malignancies. Patients were identified by two methods: 1) search of our institutional pathology database from 2000-2015 for INI1-deficient tumors and 2) presence of SMARCB1 genomic alteration in a database of 280 cases with somatic panel sequencing results. Patients were included in the study if sufficient archival tumor tissue was available for repeat, confirmatory sequencing and immunohistochemistry (IHC). Somatic next-generation sequencing (NGS) was performed via a panel assay, OncoPanel, which surveys exonic DNA sequences of 447 cancer genes and 191 regions across 60 genes for rearrangement detection. IHC stains for INI1 and PD-L1 were performed according to standardized procedure on Leica Bond automated platforms and expression was assessed by two investigators (AA, JP) who were blinded to sequencing results. The study included 43 patients. IHC was performed on at least one specimen for all patients and repeat, confirmatory NGS was successful in 91% (39/43). Single-copy deletion of SMARCB1 on NGS panel was not predictive of loss of INI1 expression by IHC with only 1/10 (10%) SMARCB1 single-copy deletion cases having INI1 loss. In the 26 cases with INI1 loss by IHC and successful tumor sequencing, 23 (89%) had a genomic alteration in SMARCB1 detected. Five cases (22%) had 1-copy deletion, 12 (52%) had 2-copy deletion, 2 (9%) had nonsense mutations, and 4 (17%) had two inactivating alterations. 40% (12/30) of the patients with INI1-deficient tumors had at least one tumor specimen that was PD-L1 positive (≥1%). PD-L1 status was not associated with timing of tumor sampling or prior treatment. TMB ranged from 0.76 to 9.13 mut/Mb of DNA. We have observed 2 patients with INI1-deficient cancers with evidence of efficacy of immune checkpoint inhibitors. SMARCB1 2-copy deletions and inactivating mutations are associated with loss of INI1 protein expression, but 1-copy deletion of INI1 in histologies other than those already known to be INI1-deficient is not predictive of loss of protein expression. These results, along with two case reports of successful disease control with immune checkpoint inhibitors, suggest that clinical trials of PD-1 or PD-L1 inhibitors, either as single agents or in combination with an EZH2 inhibitor, are warranted in malignancies with INI1 loss. Citation Format: Suzanne J. Forrest, Alyaa Al-Ibraheemi, Abigail Ward, Duong Doan, Catherine Clinton, Juan Putra, R. Seth Pinches, Cigall Kadoch, Susan Chi, Steve G. Dubois, Patrick Leavy, Natalie Collins, Alanna Church, Katherine A. Janeway. Genomic and immunologic characterization of a cohort of INI1-deficient pediatric cancers [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A16.

Integrative clinical and biopathology analyses to understand the clinical heterogeneity of infantile rhabdomyosarcoma: A report from the French MMT committee.

BackgroundRhabdomyosarcoma (RMS) in infants is a particular entity with various clinical presentations and outcomes. To better understand the clinical heterogeneity of RMS in infants, an integrative clinical, histological, and molecular analysis was performed.MethodsFrom 1989 to 2015, 37 infants aged less than 6 months with a diagnosis of RMS and archival tumor materials were identified in France. Clinical data, central pathologic review, and molecular profile including RNA sequencing were analyzed.ResultsNineteen patients (51%) had embryonal RMS (ERMS) (including three highly differentiated ERMS with PTCH deletion), eight (22%) had spindle cell RMS (SRMS) (three VGLL2‐, one NTRK‐, and two (B)RAF‐fusions), six (16%) had alveolar RMS (ARMS) (all FOXO1‐ or PAX3‐fusion), two had unclassified RMS, and two poorly differentiated RMS were retrospectively diagnosed as rhabdoid tumors (RT) with loss of INI1 expression. The two RT patients died of rapid disease progression. Five‐year event‐free (EFS) and overall survival (OS) for RMS were 62% (95%CI, 47‐82) and 52% (95%CI, 37‐72). Eleven patients (31%) relapsed and four (11%) had primary refractory disease (all ERMS). In univariate analysis, EFS and OS were only associated with histology subtype, with 100% survival of known fusion‐positive SRMS. RNA cluster expression showed three main clusters: ARMS, ERMS, and “VGLL2‐fusion” cluster, consisting of SRMS and ERMS.ConclusionsBiopathology findings from this study support the different prognosis of infantile RMS. New fusion‐positive SRMS has a very good outcome which may allow more conservative treatment in the future.

The Rare Phenomenon of Loss of INI1 Expression at Recurrence/Progression of Primary Central Nervous System Tumors: Report of 3 Cases

It is extremely rare for loss of immunohistochemical expression of INI1 to occur primarily at recurrence/progression with retained expression at the primary/initial presentation of central nervous system (CNS) tumor. In this article, we present 3 such cases showing loss of INI1 expression primarily at recurrence. All patients were males, aged 7 years (case 1), 11 years (case 2), and 35 years (case 3), diagnosed with low-grade glial/glioneuronal tumor, not otherwise specified (case 1), craniopharyngioma (case 2), and glioblastoma (case 3); all showed retained INI1 protein expression. Case 1 at 12 months recurrence showed a high-grade tumor with relative undifferentiated morphology, case 2 after 104 months showed a sarcomatous progression, and case 3 recurred after 4 months with the presence of relative undifferentiated round cells. All these recurrences showed loss of INI1 expression. Loss of SMARCB1/INI1 gene function resulting in complete loss of INI1 protein expression is not a well-accepted genetic mechanism for transformation/progression as this series emphasizes.

Loss of INI1 Expression-Understanding the Molecular Basis of Chordoid Meningiomas.

Loss of INI1 Expression-Understanding the Molecular Basis of Chordoid Meningiomas.

Clinicopathologic and Molecular Pathology of Collecting Duct Carcinoma and Related Renal Cell Carcinomas.

Collecting duct carcinoma (CDC) and related tumors [ie, renal medullary carcinoma (RMC)] are rare types of highly aggressive renal cell carcinomas (RCC) with poor prognosis. Because of the rarity and diagnostic uncertainty of them, their molecular pathology and significance have not yet been fully elucidated. CDC, RMC, fumarate hydratase-deficient RCC (including hereditary leiomyomatosis and RCC-associated RCC HLRCC-RCC), and recently reported anaplastic lymphoma kinase (ALK)-rearrangement RCC have significant morphologic overlaps, but they are separately distinct entities having different molecular pathway and clinical settings. CDC is more likely to occur in middle to old age population with immunoreactivity for PAX8 and integrase interactor-1 proteins (INI-1). Various chromosomal and genomic alterations have been reported with inconsistent results. In contrast, RMC is more likely to occur in younger patients with sickle cell trait. In RMC, loss of INI-1 expression and OCT3/4 expression are distinguished compared with other RCCs. Finally, ALK-rearrangement RCC seems to have 2 different clinical settings, one with sickle cell trait (VCL-ALK fusion) and the other without (other fusions such as TPM3-ALK, EML4-ALK, and STRN-ALK fusions). Interestingly, VCL-ALK fusion was found in pediatric patients with sickle cell trait, whereas other fusions were detected in adolescent or adult without sickle cell trait. Taken together, CDC and related tumors such as RMC, fumarate hydratase-deficient RCC (including hereditary leiomyomatosis and RCC-associated RCC), and ALK-rearrangement RCC are the distinct entities and their recognition is important for the development of future personalized therapeutic options. This review updates the clinicopathologic features of these tumors with overlapping morphology and outcome.

Small cell undifferentiated (SCUD) hepatoblastomas: All malignant rhabdoid tumors?

Small cell undifferentiated (SCUD) hepatoblastoma is a rare variant of hepatoblastoma with poor outcome and loss of INI1 expression, sharing this with malignant rhabdoid tumors (MRT). We studied all tumors from the files of the Kiel Pediatric Tumor Registry (KTR) with the initial diagnosis of SCUD and MRT. After re-review, we performed immunistochemistry, fluorescence in situ hybridization, and multiplex ligation dependent probe amplification for loss of expression and deletion of INI1/SMARCB1 in 23 tumors. Morphologically, 12 of the tumors had a small cell morphology, 9 showed the typical picture of MRT, and 2 were composed of both small cells and rhabdoid cells. All but 1 of the 23 tumors showed loss of INI1 protein expression by immunohistochemistry. Nineteen of the INI1 negative tumors were analyzed by FISH technique and all showed a deletion of the INI1/SMARCB1 gene (17 homozygous deletions, 2 heterozygous deletions). We investigated 14 of these cases by multiplex ligation dependent probe amplification and verified the deletions in all cases. In conclusion, we postulate that SCUD hepatoblastoma is not a hepatoblastoma but represents a malignant rhabdoid tumor of the liver. © 2016 Wiley Periodicals, Inc.

Ewing Sarcoma and Atypical Teratoid Rhabdoid Tumor: A FISH and Immunohistochemical Comparison

Ewing sarcoma (ES)/primitive neuroectodermal tumor (PNET) and atypical teratoid rhabdoid tumor (ATRT) are high-grade malignancies of childhood, each of which is associated with genetic abnormalities on chromosome 22. ES is typically characterized by rearrangement of the EWSR1 locus and ATRT by deletion of SMARCB1. We report a case with an unusual FISH signal pattern consistent with EWSR1 rearrangement that was shown to have loss of INI1 expression by immunohistochemistry due to deletion in the long arm of one chromosome 22. In light of the unusual findings in this case as well as the proximity of the EWSR1 locus and SMARCB1 locus on chromosome 22 and frequent CD99 staining in both tumors, we examined 16 ES cases and 17 ATRT, renal rhabdoid tumor (RRT), and extrarenal rhabdoid tumor (ERRT) cases for CD99 and INI1 staining and for EWSR1 rearrangement. Staining with INI1 was negative in ATRT, RRT, and ERRT and positive in ES cases; CD99 was positive in ES cases and variable in ATRT cases. All but 2 cases of ES, and no cases of ATRT, showed rearrangement of EWSR1. The present case appears to be best classified as a unique variant of ATRT based on immunohistochemistry, EWSR1 FISH and RT-PCR, and SMARCB1 gene sequencing.

Loss of INI1 expression in colorectal carcinoma is associated with high tumor grade, poor survival, BRAFV600E mutation, and mismatch repair deficiency

SMARCB1 is a tumor suppressor gene that encodes for the protein INI1. SMARCB1 is commonly inactivated and INI1 correspondingly shows loss of expression in a range of malignant neoplasms including rhabdoid tumors, renal medullary carcinomas, and epithelioid sarcomas. Loss of INI1 expression has recently been reported in occasional gastrointestinal adenocarcinomas. We sought to investigate the incidence and clinicopathological significance of INI1 loss in colorectal adenocarcinoma (CRC). Immunohistochemistry for INI1 was performed in tissue microarray (TMA) format on a well-characterized and unselected cohort of CRCs undergoing surgical resection. If staining was negative or equivocal in the TMA sections, immunohistochemistry was repeated on whole sections. Focal or widespread negative staining for INI1 was identified in whole sections from 14 (0.46%) of 3051 CRCs. In 7 (50%) of 14 negative cases, the loss of staining was focal, whereas the remainder were characterized by negative staining in all neoplastic cells in whole sections. In the cases with focal staining, loss of staining was frequently found in areas of poor differentiation. Global or focal INI1 loss was strongly associated with higher histological grade, larger tumor size and poor overall survival (P<.001). We conclude that INI1 loss occurs rarely (0.46% when screened by TMA) in CRC, where it is associated with higher grade, larger tumor size, poorer survival, mismatch repair deficiency, and BRAFV600E mutation.

Abstract A27: INI1 negative hepatoblastoma, a vanishing entity representing malignant rhabdoid tumor

Abstract Introduction: Hepatoblastoma (HB) is the most common primary hepatic tumor of childhood. According to the most current Children’s Oncology Group (COG) classification small cell undifferentiated hepatoblastomas (SCU-HB) are a subtype of epithelial hepatoblastomas with adverse outcome. Malignant rhabdoid tumors (MRT) of the liver are a distinct highly aggressive group of tumors with unknown cell of origin diagnosed on the basis of INI1 negative immunoreactivity and rhabdoid morphology. In the absence of rhabdoid morphology, presence of SMARCB1/INI1 deletion on chromosome 22q11.2 is confirmatory. Therefore, MRT lacking classic rhabdoid morphology are often misdiagnosed as SCU-HB, especially on small biopsy samples. We present a case of previously healthy full-term 10 month old female infant with a lobulated heterogeneous right hepatic mass, low serum alpha-fetoprotein (AFP) of 71 ng/ml, and metastatic pulmonary disease. Initial biopsy of mass was consistent with hepatoblastoma, predominantly small cell undifferentiated component. The patient underwent chemotherapy with vincristine, irinotecan, and temsirolimus with less than the 30% response required for partial responder. She subsequently underwent right partial hepatectomy. Results: Histologic evaluation of the biopsy sample revealed solid proliferation of small tumor cells with clear to eosinophilic cytoplasm and prominent nucleoli, compatible with small cell morphology. Immunohistochemistry for INI1 was negative in all tumor cells. In the absence of rhabdoid morphology, the tumor was initially classified as INI1 negative SCU-HB. Subsequently, the resection specimen showed predominantly small cells with only focal areas of rhabdoid morphology. An extensive immunohistochemical panel was performed and the tumor cells were negative for hepatocellular differentiation markers (Hepar-1 and arginase), beta-catenin, desmin, myoD1, cytokeratin 7, cytokeratin 20, and were positive for glypican-3 and cytokeratin in both biopsy and resection specimens. Similar to the biopsy sample, the tumor cells were entirely negative for INI1 on the resection specimen. Cancer Whole-Exome Sequencing (WES) with Transcriptome was performed and showed homozygous deletion of SMARCB1 on chromosome 22q11.23 with evidence of loss of expression of the gene confirming the loss of INI1 expression with IHC. Discussion: MRT of liver are a distinct entity and are in the differential diagnosis of INI-1 negative pediatric liver tumors along with SCU-HB. MRT are also considered in the differential diagnosis of any aggressive liver tumor with low levels of AFP. Current reports indicate that differentiation of MRT from INI1 negative SCU-HB, in the absence of rhabdoid morphology, is mainly based on molecular testing for SMARCB1. In our case, the initial biopsy sample was classified as INI1 negative SCU-HB predominantly based on morphology, and was subsequently reclassified as MRT based on demonstration of SMARCB1 deletion with WES, as well as identification of focal areas of rhabdoid morphology on the resection specimen. Conclusion: Based on this finding, morphology is not a robust method of differentiating MRT from SCU-HB. It is possible that many cases previously classified as SCU-HB mainly based on morphology, if retrospectively analyzed for SMARCB1 would be reclassified as MRT. Citation Format: Ladan Fazlollahi, Susan Hsiao, Mahesh Mansukhani, Julia Glade Bender, Andrew Kung, Darrell Yamashiro, Helen Remotti. INI1 negative hepatoblastoma, a vanishing entity representing malignant rhabdoid tumor. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr A27.

SWI/SNF complex deficiency and mismatch repair protein expression in undifferentiated and dedifferentiated endometrial carcinoma

Undifferentiated endometrial carcinoma (UEC) is a relatively uncommon but clinically aggressive uterine malignancy. In common with a subset of poorly differentiated carcinomas arising in other sites, UEC may exhibit rhabdoid morphology and be associated with a low-grade tumour component (dedifferentiated carcinoma). Recent studies have implicated inactivation of the SWI/SNF complex subunits in the aforementioned extrauterine tumours. Therefore we have examined INI1 (SMARCB1), BRG1 (SMARCA4), and BAF250a (ARID1A) immunostaining, and also expression of the DNA mismatch repair (MMR) proteins MLH1, PMS2, MSH2 and MSH6 in 22 UEC, seventeen of which were dedifferentiated. Abnormal SWI/SNF subunit expression was detected in four dedifferentiated carcinomas including three with loss of BRG1 staining limited to the undifferentiated tumour component and one case with loss of INI1 expression in both low- and high-grade elements; the latter case also showed BAF250a deficiency in the undifferentiated tumour cells. Abnormal MMR protein expression was identified in 13 tumours (59%) including nine with concurrent loss of MLH1 and PMS2. These findings suggest that SWI/SNF subunit alterations may play a role in the progression/ dedifferentiation of endometrial carcinoma, and that SWI/SNF and MMR protein deficiencies may act synergistically in deregulating DNA repair mechanisms in these tumours.

Epithelioid malignant peripheral nerve sheath tumor: clinicopathologic analysis of 63 cases.

Epithelioid malignant peripheral nerve sheath tumor (EMPNST) is rare and differs from conventional malignant peripheral nerve sheath tumor by showing diffuse S-100 protein positivity, infrequent association with NF1, and occasional origin in a schwannoma. Loss of INI1 expression is seen in a subset of tumors. The purpose of this study was to further define clinicopathologic features and outcome data in a large series of EMPNST. Sixty-three cases were identified in consultation files. The patient group consisted of 33 men and 30 women; the median age was 44 years (range, 6 to 80 y). One patient was reported to have NF1. One patient had 3 seemingly separate primary EMPNSTs during his 12-year clinical course. The median tumor size was 3.0 cm (range, 0.4 to 20 cm), and tumors were located most frequently on the lower extremity (30/63; 48%) and trunk (16/63; 25%). Most tumors were superficial (5 dermal, 38 subcutaneous); 15 were subfascial, and 5 were visceral. Microscopically, tumors comprised a relatively uniform but clearly atypical population of epithelioid cells. The majority of tumors demonstrated a multilobular growth pattern, with lobules and nests surrounded by myxoid and/or fibrous stroma. Tumor cells were round, polygonal, or ovoid and had round vesicular nuclei and abundant amphophilic to palely eosinophilic cytoplasm. Focal spindled morphology was seen in one third of cases. Most tumors (55/63; 87%) showed marked cytologic atypia with irregular vesicular nuclei and prominent nucleoli. Mitotic rate ranged from 1 to 46/10 HPF (median, 5/10 HPF); atypical mitotic figures were seen in 7 cases. Necrosis was present in 17 tumors. Twelve tumors were associated with a nerve. Nine tumors arose in a schwannoma (6 conventional type, 3 epithelioid) and 1 in a neurofibroma (in the NF1 patient). All tumors expressed S-100 protein, and the majority showed strong and diffuse staining (87%; 55/63). There was no expression of the melanocytic markers Mart-1/Melan-A (0/58), HMB-45 (0/57), and MiTF (0/9). Other immunohistochemical results included variable staining for GFAP (24/40; 60%) and EMA (4/29; 14%), whereas keratin was consistently negative (0/33). INI1 expression was lost in 67% of tumors examined (35/52). Most tumors were treated by surgical resection; 13 also received chemotherapy and/or radiation. Follow-up data were available for 31 cases and ranged in duration from 3 months to 20 years (median, 36 mo). Twenty-two patients have no evidence of disease at the time of follow-up. Nine patients developed local recurrence, 3 of whom were reported to be disease-free at the time of latest follow-up (44 mo, 19 y, and 20 y). Five patients developed distant metastases, and 4 patients died of disease (including 2 with unresectable recurrent tumors). Recurrence, metastasis, and disease-related death were observed independent of anatomic site or depth. In summary, EMPNST is a morphologically distinct variant that most commonly affects adults on the lower extremity or trunk, although a wide age range and site distribution are seen. Most tumors arise in superficial soft tissue, are diffusely S-100 positive, and two thirds show INI1 loss. On the basis of available follow-up information there is a comparatively low risk for recurrence and metastasis, irrespective of tumor depth.

Transitory Complete Response to the EpSSG Extracranial Rhabdoid Tumor Protocol in a White Adolescent with a Sickle Trait Harboring a Metastatic Renal Medullary Carcinoma

Renal medullary carcinoma (RMC) is a very rare disease that is almost exclusive to young black patients with sickle cell trait. Most patients present with metastatic disease at diagnosis and have a grim prognosis. Histologic diagnosis of these tumors can be difficult in the presence of rhabdoid elements and loss of INI1 expression as observed in our case. We describe the first known reported case of a white male adolescent with sickle cell trait, who was treated for a metastatic RMC with reticular pattern of rhabdoid-like cells and absence of INI1 expression, by the European Soft Tissue Sarcoma Study Group (EpSSG) protocol designed for rhabdoid tumors and who achieved a transitory complete response. Although complete remission was achieved, overall survival was not improved.