SMARCA4-deficient Thoracic Sarcoma Research Articles

Cytopathological characteristics of SMARCA4-deficient thoracic undifferentiated tumors in serous effusion

Objective: To investigate the clinicopathological characteristics of SMARCA4-deficient thoracic undifferentiated tumors, and the diagnostic value of the cells in serous effusion. Methods: Eleven cases of SMARCA4-deficient tumor were collected from the Affiliated Hospital of Hebei University, China from January 2018 to July 2023, which were diagnosed using cell block of serous effusion. The clinical, histopathological, immunohistochemical and molecular genetic features were reviewed, along with related literature. Results: All the 11 patients were males with ages ranging from 54 to 77 years (median 64 years). Nine patients were smokers and two had an unknown smoking history. Most of them complained of cough and dyspnea with pleural effusion. The primary tumor sites included lung (9 cases), thoracic wall (1 case), and mediastinum (1 case), while 3 patients had a history of lung surgery. Histologically, tumor cells were large and pleomorphic, with increased nuclear-cytoplasmic ratio. They also showed round nuclei, conspicuous nucleoli, and basophilic cytoplasm in serous effusion. Immunohistochemically, tumor cells in all cases were negative for SMARCA4/BRG1, CKpan and CK7, but positive for SMARCB1/INI1. Some of the cases were positive for CD34 (7/11), synaptophysin (4/11) and SALL4 (2/11). Histologically, monotonous tumor cells formed solid sheets or anastomosing islands with poor cell adhesion and rhabdoid morphology. Brisk mitotic figures were accompanied by large areas of necrosis. Some cases focally exhibited syncytia, and some had bright cytoplasm and vesicular chromatin. The immunohistochemical profiles in the tumor tissues were consistent with those of cytology. Six cases were negative for PD-L1 (22c3). Among the 6 cases analyzed by targeted next generation sequencing, concurrent SMARCA4 and TP53 mutations were detected in all 6 cases. Some of the 6 tumors showed mutations of STK11, CDKN2A, and MET, and amplification of ERBB2, exon deletion of BRCA2, etc. Follow-up information was available in all cases and ranged from 2 to 24 months. The patients showed metastases to various sites, including lymph node, liver, kidney, adrenal gland, brain, bone and other sites. Four patients died of the tumor. The survival time of 4 patients who underwent radical resection or radiofrequency ablation was more than 13 months. Conclusions: SMARCA4-deficient thoracic sarcoma is a rare but highly aggressive tumor with dismal prognosis and rhabdomyoid features. It is difficult to diagnose this disease using only serous effusion samples. This tumor thus warrants careful consideration. Accurate diagnosis can greatly improve early diagnosis and treatment of these tumors.

SMARCA4-deficient thoracic sarcoma revealed by metastasis to the small intestine: a diagnostic dilemma

SMARCA4-deficient thoracic sarcoma (SMARCA4-DTS) is a recently identified aggressive subtype of sarcoma. We present the case of a 44-year-old man who underwent a surgery for a perforated small intestine. Compued tomography scan revealed a tissular mediastino–pulmonary mass.Histopathological examination of the intestinal mass shown a malignant tumour with a typical epithelioid and rhabdoid cells, numerous mitoses and large necrosis. A large panel of immunohistochemistry revealed loss of SMARCA4 and SMARCA2 and allowed the diagnosis of SMARCA4-DTS. It is important to consider SMARCA4-deficient thoracic sarcoma in the differential diagnosis of tumours showing suggestive morphologic features in patients of all ages, especially in the case of metastasis associated with thoracic mass.

Sarcomas of the mediastinum with epithelioid morphology.

While soft tissue sarcomas typically have a spindled or pleomorphic appearance, a subset of malignant soft tissue neoplasms can have a prominent epithelioid morphology. In complex anatomic sites such as the mediastinum, such tumors can often be mistaken for a carcinoma or mesothelioma. Frequent expression of cytokeratin staining can further confound the diagnostic process and familiarity with these entities can help prevent an erroneous diagnosis. Particular entities that have been reported to occur in the mediastinum with such features include dedifferentiated liposarcoma, pleomorphic liposarcoma, malignant peripheral nerve sheath tumor, synovial sarcoma, SMARCA4-deficient thoracic sarcoma, alveolar soft part sarcoma and clear cell sarcoma. Many of these tumors exhibit unique clinical, genetic, molecular or immunohistochemical features which allow for accurate characterization. For example, pleomorphic liposarcoma contains bizarre appearing lipoblasts and dedifferentiated liposarcoma exhibits MDM2 gene amplification that is typically confirmed by fluorescence in-situ hybridization. Malignant peripheral nerve sheath tumor will often arise in association with a nerve or neurofibroma. Synovial sarcoma consistently exhibits rearrangements involving the SS18 gene and SMARCA4-deficient thoracic sarcoma shows loss of SMARCA4 staining in the tumor cells. Alveolar soft part sarcoma demonstrates an ASPL-TFE3 fusion transcript. Clear cell sarcoma often shows an EWSR1-ATF1 fusion transcript. When encountering a sarcoma of the mediastinum with epithelioid features, familiarity with these and other characteristics can help insure a correct diagnosis.

SMARCA4 Deficient Thoracic Sarcoma Presenting with a Pathologic Fracture of Proximal Tibia and L5 Vertebral Body: a Case Report and Review of Literature

Abstract Introduction/Objective SMARCA4 (BRG1) is a central component of the Switch/Sucrose-Non-Fermentable (SWI/SNF) chromatin remodeling complex which plays a critical role in the initiation, progression and dedifferentiation of a variety of cancers arising in different anatomical sites. The recently discovered SMARCA4-deficient thoracic sarcoma (DTS) can present as a mediastinal, pleural or pulmonary mass and constitutes a unique and highly lethal entity. Methods Here we present an interesting case of a 66-year-old, smoker male with past medical history of COPD, polysubstance abuse, hepatitis C virus, and alcoholic cirrhosis who presented with left proximal tibia pathological fracture, L5 vertebral body lytic lesion, left leg cellulitis and hypercalcemia. Imaging studies, tibia biopsy, thoracocentesis, histopathological examination, and immunohistochemical stains were performed. Results Imaging studies revealed a 3.1 cm, right upper lobe speculated lung mass along with multiple other lung nodules. Numerous arterially enhancing hepatic masses up to 2.8 cm were also identified. The patient underwent intramedullary nail, cementation and tibia biopsy followed by thoracentesis a month later.The histological sections revealed sheets of poorly differentiated malignant epithelioid cells showing high nuclear pleomorphism, prominent nucleoli, eosinophilc cytoplasm with extensive necrosis, and high mitosis (Ki-67 around 100%). The tumor cells lacked the expression of SMARCA4 (BRG1), cytokeratin, SALL4, CD34, TTF-1, P40, S100, HMB45, pan melanoma, desmin, CD31, ERG, CD30, CD56, chromogranin, CD38, CD45, CD3, ALK-1, myeloperoxidase, glypican-3, hepatocyte, and inhibin with mixed kappa and lambda. Tumor cells expressed SATB2 and focal synaptophysin, consistent with SMARCA4 deficient thoracic sarcoma metastasizing to the bone. The patient’s condition rapidly deteriorated and he died within two months. Conclusion An accurate diagnosis of these tumors is paramount and can be challenging. However, recognizing SMARCA4-DTS from other types of epithelioid tumors that involve the thoracic region is clinically relevant, as targeted therapies for SMARC-deficient tumors are currently being investigated and new clinical trial data show therapeutic benefit.

Cytology of SMARCA4-Deficient Thoracic Neoplasms: Comparative Analysis of SMARCA4-Deficient Non-Small Cell Lung Carcinomas and SMARCA4-Deficient Thoracic Sarcomas

Introduction: Inactivating mutations of the SMARCA4 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 4) gene and/or loss of the BRG1 (brahma-related gene 1) protein defines SMARCA4-deficient thoracic sarcoma (SMARCA4-dTS), an aggressive neoplasm with a usually fatal outcome. Similar SMARCA4 mutations/BRG1 loss is also seen in a subset of non-small cell lung carcinomas (NSCLCs; SMARCA4-dNSCLCs) that lack alterations in currently targetable oncogenic drivers, that is, EGFR, ALK, and ROS1. There is limited knowledge on the cytomorphological features of these SMARCA4-deficient thoracic neoplasms. Methods: We retrospectively analysed the cytology of 2 cases each of SMARCA4-dNSCLC and SMARCA4-dTS to understand their cytomorphological overlap, if any, and identify features that would prompt testing for BRG1 loss. Results: All 4 patients were males presenting with advanced disease, with a mean age of 41.5 years (SMARCA4-dTS) and 58.5 years (SMARCA4-dNSCLC) at presentation. The cytology of the 2 SMARCA4-dTSs was strikingly similar, showing predominantly singly dispersed rhabdoid phenotype tumour cells with perinuclear cytoplasmic condensations in an inflammatory or necrotic background. The cytology raised suspicion for a wide range of differentials, including melanoma, high-grade lymphoma, germ cell tumour, undifferentiated carcinoma, and undifferentiated sarcoma. SMARCA4-dNSCLCs, on the other hand, were recognizable as poorly differentiated (adeno)carcinomas and were easily distinguished from SMARCA4-dTSs, with both cases showing cohesive clusters of frequently large tumour cells with abundant pale cytoplasm. Conclusion: A diagnosis of SMARCA4-dTS is possible on cytology with appropriate ancillary testing and a high index of suspicion. The cytology of SMARCA4-dNSCLCs does not overlap with SMARCA4-dTS; rather, it resembles that of any poorly differentiated (adeno)carcinoma in the limited numbers analysed in this study.

EP1.15-03 SMARCA4-Deficient Thoracic Malignancies: A Unifying Genetic Aberration Across Tumors of Divergent Differentiation

Mutations in ATPase-dependant chromatin remodelling units are one of the most common genetic alterations observed in human cancer. Germline mutations in SMARCA4 encoding for Brg-1 protein, a subunit of the SWI/SNF chromatin modifier unit, are well recognised as the causative genetic event in rhabdoid tumor predisposition syndromes that occur in infants and young children. In recent years, somatic mutations in SMARCA4 have been increasingly identified in many adult-onset malignancies ranging from well differentiated carcinomas to poorly differentiated high grade sarcomas in a variety of anatomical sites, including thorax. Documentation of such tumors is essential to our understanding of the pathogenesis and possible mechanisms of therapeutic targetting. Case 1: A 60-year-old male smoker presented with chronic emphyema thoracis of non-tubercular etiology which was treated by intercostal drainage. He had repeated episodes of blockade of chest drain over the next 6 months and eventually a thoracic window was surgically created. Five months following thoracotomy, patient presented with a mass growing at the site of the thoracic window. No other masses in the lung parenchyma or mediastinal lymphadenopathy was seen. Patient underwent an excision of the granulation tissue-like mass. Formalin fixed paraffin embedded sections were subject to microscopy and immunohistochemistry for vimentin, CD34, MIC2, p53, SALL4, pan-cytokeratin (AE1/AE3), EMA, p40, TTF-1, cytokeratin-7, Hepar-1, desmin, myogenin, CD31, S100, Melan-A, HMB-45, GATA-3, calretinin, WT1, INI-1, brg-1 and hematolymphoid markers. Case 2: A 58-year old male smoker presented with hemoptysis and cough. On evaluation, an endobronchial mass was identified and was excised. Formalin fixed paraffin embedded sections from excised tumor mass was subject to microscopy and immunohistochemistry for cytokeratin 7, cytokeratin 19, epithelial membrane antigen, chromogranin, synaptophysin, cytokeratin 20, CD117, TTF-1, NUT1, Her2neu, GATA3, p40, S100, INI-1 and brg-1. Case 1: Microscopy revealed a tumor centred in the soft tissue of the chest wall ulcerating the overlying skin. No lung parenchymal involvement was seen. The tumor was arranged in sheets composed of monomorphic large tumor cells with abundant eosinophilic cytoplasm and prominent nucleoli showing frequent mitoses and foci of necrosis. No squamous or glandular differentiation was seen. Tumor cells were only immunopositive for vimentin, CD34, MIC2, p53, and SALL4, very focally immunopositive for CK (AE1/AE3) and showed retained INI-1 protein expression. Brg-1 expression was lost in tumor cells leading to a diagnosis of SMARCA4-deficient thoracic sarcoma. Case 2: Microscopy revealed a high grade tumor arising from the main bronchi with parenchymal and tracheal extension ulcerating the overlying squamous epithelium. Tumor cells were arranged in lobules with peripheral palisading and central necrosis. The tumor cells were large with frequent cytoplasmic clearing and frequent mitoses. Tumor cells were immunopositive for CK-7, CK-19, EMA, CG while were negative for others. INI-1 was retained while brg-1 was lost leading to a diagnosis of SMARCA4-deficient carcinoma. Two independant studies have delineated SMARCA4-deficient thoracic sarcomas and SMARCA4-deficient lung carcinomas as distinct clinicopathological entities. Despite a unifying genetic alteration, these tumors appear to show varied histomorphology and immunoprofiles. Long term follow-up and molecular analysis of such tumors is necessary.

SMARCA4-deficient primary thoracic sarcoma:a clinicopathological analysis of five cases

Objective: To investigate the clinicopathological characteristics of SMARCA4- deficient thoracic sarcomas. Methods: The clinical features and CT scans of SMARCA4-deficient thoracic sarcomas (n=5) diagnosed at Fudan University Cancer Hospital from December 2016 to October 2018 were reviewed. Hematoxylin-eosin staining, immunohistochemistry and targeted next generation sequencing were performed in available cases along with a literature review. Results: All 5 patients were males with age ranging from 32 to 65 years (average 54 years; median 61 years). Four patients were smokers except one with unknown smoking history. The average maximum diameter of tumor was 5.6 cm. Tumor primary sites included thoracic wall,thoracic cavity,lung and mediastinum. Histologically,tumor cells formed solid sheets or anastomosing islands with brisk mitotic figures accompanying with large areas of necrosis. Three cases focally exhibited rhabdoid morphology and vesicular chromatin. Immunohistochemically, SMARCA4, SMARCA2 and Claudin-4 were negative in all cases and all tumors demonstrated SOX2 and SMARCB1 nuclear positive staining. Among 3 cases analyzed by targeted next generation sequencing, concurrent SMARCA4 and p53 mutation was detected in all three cases. Mutations of STK11, ERBB4, NF2, GNAS, MTOR,MET and FGFR1 amplification were also detected among the three cases. The follow-up information was available in all 5 cases. Two patients died of the tumor. One relapsed multiple times after surgeries but was alive with disease. Two patients received radical excisions without relapse. Conclusions: SMARCA4-deficient thoracic sarcoma is a rare but highly-aggressive tumor with dismal prognosis. The tumor is featured by rhabdoid morphology histologically and distinctive immunohistochemical and molecular phenotype.

SMARCA4-deficient Thoracic Sarcomas: Clinicopathologic Study of 30 Cases With an Emphasis on Their Nosology and Differential Diagnoses.

SMARCA4-deficient thoracic sarcoma (SMARCA4-DTS) is a recently described entity with an aggressive clinical course and specific genetic alterations of the BAF chromatin remodeling complex. In the present study, we reviewed the clinical and pathologic features of 30 cases of SMARCA4-DTS, discussed its main differential diagnoses and the challenging diagnostic scenarios that the average pathologist may face. In addition, we tested the specificity of the "SMARCA4-DTS immunohistochemical signature" (co-loss of SMARCA4 and SMARCA2 with overexpression of SOX2) in a large cohort of intrathoracic malignancies. Patients ranged from 28 to 90 years of age (median: 48 y), with a marked male predominance (male:female=9:1) and they were usually smokers. Tumors were generally large compressive masses located in the mediastinum (n=13), pleura (n=5), lung (n=2) or in 2 or more of these topographies (n=10). Treatment strategies were varied, including 1 case treated with EZH2 inhibitors. Median overall survival was 6 months. Histologically, tumors were poorly differentiated frequently showing rhabdoid features. A subset of cases showed a focal myxoid stroma (7%, n=2/30) and rare cases displayed a previously unreported pattern simulating desmoplastic small round cell tumors (7%, n=2/30). Making a diagnosis was challenging when dealing with biopsy material from massively necrotic tumors and in this setting the expression of SOX2, CD34, and SALL4 proved useful. All tested cases displayed concomitant loss of SMARCA4 and SMARCA2 and most tumors expressed epithelial markers (Pan-keratin or EMA) (n=29/30), SOX2 (n=26/27), and CD34 (n=17/27). SMARCB1 expression was retained in all cases (23/23). SALL4 and Claudin-4 were expressed in a subset of cases (n=7/21 and 2/19, respectively). TTF-1 and P63 were focally expressed in 1 case each. P40 and NUT were not expressed (0/23 and 0/20, respectively) The SMARCA4-DTS immunohistochemical signature was both sensitive and specific, with only a subset of small cell carcinoma of the ovary hypercalcemic type showing overlapping phenotypes. Our study confirms and expands the specific features of SMARCA4-DTS, emphasizing the fact that they can be straightforwardly identified by pathologists.

Imaging features of SMARCA4-deficient thoracic sarcomas: a multi-centric study of 21 patients.

SMARCA4-deficient thoracic sarcoma (SMARCA4-DTS) is a recently identified aggressive subtype of sarcoma. The aim of this study was to characterize the CT imaging features of SMARCA4-DTS. From June 2011 to May 2017, 21 adult patients with histologically proven SMARCA4-DTS were identified in the radiological database of 2 French sarcoma reference centers with at least one chest CT scan available. The locations, sizes, heterogeneity, margin definitions, and local extensions of the tumors were reported together with their impact on surrounding organs and regional and distant metastases. Pathological findings, molecular analyses, and patients' outcomes were retrieved. Of the 21 included patients (median age 48, range 30-74), 18 (85.7%) were male and 18 (85.7%) had a smoking history. Four main radiological patterns were identified depending on the location of the main tumor burden: mediastinal (n = 13), pleural (n = 6), cervical (n = 1), and retroperitoneal (n = 1). Median size was 120mm (range 46-266). Characteristic CT imaging features of primary tumors included ill-defined margins (n = 21), heterogeneous enhancement after injection (n = 20), multi-compartment extension from mediastinum to lung apex, pleura, or neck (n = 20), compressive effect responsible for atelectasis (n = 11), vascular encasement (n = 16-5 superior vena cava syndrome), and esophagus invasion (n = 5). Primary tumors showed strong 18F-FDG avidity in eight patients with PET-CT. Necrotic lymphadenopathies were found in 19 patients, with a surrounding infiltrate in 13 patients. Metastatic locations at baseline mainly involved adrenal (n = 10), lung (n = 6), and bone (n = 5). Median overall survival was 5months (range 1-13). Most SMARCA4-DTS present with compressive and infiltrative chest masses with ill-defined necrotic lymphadenopathies. The diagnosis of SMARCA4-DTS should enter in the differentials of the radiologist, especially in the case of a rapidly evolving thoracic mass in young smoking males. • SMARCA4-DTS is a very aggressive poorly differentiated sarcoma with a predilection for young and middle-aged adult male smokers. • SMARCA4-DTS, which is mostly located in the chest cavity, can compress and infiltrate all adjacent organs leading to superior vena syndrome, lung atelectasis, epiduritis, spinal cord compression, and esophagus invasion. • SMARCA4-DTS typically demonstrates several ill-defined necrotic lymphadenopathies spreading in axillar, subclavian, cervical, mediastinum, and retroperitoneum.

ZEBRAS HAVE HOOVES TOO: A CASE OF THE PROSPECTIVE DIAGNOSIS OF A SMARCA4-DEFICIENT THORACIC SARCOMA IN A COMMUNITY HOSPITAL SETTING VIA INTERDISCIPLINARY AND INTERINSTITUTIONAL COLLABORATION

SESSION TITLE: Disorders of the Mediastinum 1 SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/09/2018 01:15 pm - 02:15 pm INTRODUCTION: In 2015, Le Loarer and colleagues retrospectively investigated nineteen previously unclassified sarcomas and reported a new type of aggressive thoracic malignancy, a SMARCA4-deficient thoracic sarcoma (SMARCA4-DTS).[1] An additional 12 cases were described in 2017 by Yoshida et al, with similar clinical features, immunohistochemistry, and gene expression profiles.[2] SMARCA4-DTS are readily recognizable in clinical practice as poorly differentiated, bulky thoracic malignant tumors, in predominantly middle-aged male smokers, with undifferentiated rhomboid morphology and abundant mitotic figures. Median overall survival is 7– 24 months, with mortality often due to local progression and mediastinal compression.[1] CASE PRESENTATION: A 55-year-old male with a history of tobacco and IV drug abuse presented with a two months history of progressive dyspnea, 100 lb weight loss, and new onset atrial fibrillation. Mediastinal and hilar masses were identified on CT, with encasement of broncho-vascular structures and mass effect on the SVC and aortic arch. Preliminary pathology reported a poorly differentiated necrotic neoplasm suggestive of carcinoma with neuroendocrine features. [Table 1] Considering the high level of suspicion for a SMARCA4 deficient tumor, no established standard of care, and rapidly deteriorating hemodynamic and respiratory status, the patient was not a chemotherapy candidate. Unfortunately, on the day of final pathology confirmation[Table 2], the patient had progressive respiratory failure and despite aggressive resuscitative measures continued to decline. Comfort measures were initiated on hospital day 16. DISCUSSION: Differential diagnosis of SMARCA4-DTS is wide and distinction from carcinomas can be difficult, as it requires extensive genomic profiling and immunohistochemical workup. In our case, the keys to the prospective diagnosis included 1) prior awareness of SMARCA4 deficiency, 2) an early high level of suspicion, 3) in-person collaboration between oncology and pathology services, and 4) established collaboration between our community medical center and an institution capable of extensive genetic testing. Per further literature review, CD34 is a useful, commonly available marker, as it is expressed in most SMARCA4-DTS but is not usually in lung carcinomas.[1,2] SMARCA4, SMARCA2 and SOX2 testing is important for confirmation of diagnosis. Imaging findings may also be helpful, as SMARCA4-DTS frequently arises in mediastinum and pleura, rather than in the lung. CONCLUSIONS: SMARCA4-DTS can be identified based on their unique presentation, distinctive rhabdoid morphology and immunohistochemistry. Awareness and prospective diagnosis of this rapidly progressive and rare malignancy, may provide opportunities for improved clinical management, prognostication, and identification of therapeutic or palliative options.Acknowledgement: Charles J. Nicely, MD. Dr. David Klimstra, MD. Reference #1: Le Loarer F, Watson S, Pierron G, et al. SMARCA4 inactivation defines a group of undifferentiated thoracic malignancies transcriptionally related to BAF-deficient sarcomas. Nat Genet 2015;47:1200-5. Reference #2: Yoshida A, Kobayashi E,Kubo T, et al. Clinicopathological and molecular characterization of SMARCA4-deficient thoracic sarcomas with comparison to potentially related entities. Mod Pathol 2017;30: 797-809. DISCLOSURES: No relevant relationships by Aliaksandr Ramaniuk, source=Web Response

SMARCA4-deficient Thoracic Sarcoma (SDTS): A Recently Recognized Entity with Distinct Cytomorphology that can be Diagnosed on Cytology Specimens

SMARCA4-deficient Thoracic Sarcoma (SDTS): A Recently Recognized Entity with Distinct Cytomorphology that can be Diagnosed on Cytology Specimens

SMARCA4-deficient thoracic sarcoma: a distinctive clinicopathological entity with undifferentiated rhabdoid morphology and aggressive behavior

A distinct subset of thoracic sarcomas with undifferentiated rhabdoid morphology and SMARCA4 inactivation has recently been described, and potential targeted therapy for SMARC-deficient tumors is emerging. We sought to validate the clinicopathological features of SMARCA4-deficient thoracic sarcomas. Clinicopathological information was gathered for 40 undifferentiated thoracic tumors with rhabdoid morphology (mediastinum (n=18), lung (n=14), pleura (n=8)). Thymic carcinomas (n=11) were used as a comparison group. Immunohistochemistry included BRG1 (SMARCA4), BRM (SMARCA2), INI-1 (SMARCB1), pan-cytokeratin, desmin, NUT, S-100 protein, TTF1, CD34, and SOX2. BRG1 loss was present in 12 of 40 rhabdoid thoracic tumors (30%): 7 of 18 in mediastinum (39%), 2 of 8 in pleura (25%), and 3 of 14 in lung (21%). All BRG1-deficient tumors tested for BRM (n=8) showed concomitant loss. All thymic carcinomas showed retained BRG1 and INI-1. Morphologically, tumors with BRG1 loss showed sheets of monotonous ovoid cells with indistinct cell borders, abundant eosinophilic cytoplasm, and prominent nucleoli. Scattered areas with rhabdoid morphology (ie, eccentric nuclei, dense eosinophilic cytoplasm, discohesion) were present in all the cases. SMARCA4/BRG1-deficient sarcomas showed rare cells positive for cytokeratin in 10 cases (83%). One showed rare TTF1-positive cells. All were negative for desmin, NUT, and S-100 protein. CD34 was positive in three of five (60%) BRG1-deficient tumors tested. SOX2 was positive in all four BRG1-deficient tumors tested, and negative in all seven tested cases with retained BRG1. SMARCA4/BRG1-deficient sarcomas occurred at median age of 59 years (range 44–76) with male predominance (9:3) and had worse 2-year survival compared with BRG1-retained tumors (12.5% vs 64.4%, P=0.02). SMARCA4-deficient thoracic sarcomas can be identified based on their distinctive high-grade rhabdoid morphology, and the diagnosis can be confirmed by immunohistochemistry. Identification of these tumors is clinically relevant due to their aggressive behavior, poor prognosis, and potential targeted therapy.