[Sinonasal neoplasms: Update from the WHO 2022]. / Sinunasale Neoplasien: Neues aus der WHO 2022.

The pathology of poorly differentiated sinonasal malignancies has undergone a dynamic evolution during the last decade, resulting in a refined, mostly genetically or etiologically oriented classification of neoplasms in the historical spectrum of sinonasal undifferentiated carcinoma (NUT carcinoma, SWI-/SNF-deficient carcinomas, and others). Moreover, some new entities have been established, while others could be further delineated and better characterized. A highlight of the new classification is the inclusion of SWI/SNF (SMARCB1 or SMARCA4)-deficient carcinomas into a separate category. In addition, carcinomas with DEK::AFF2 fusions have been included as a provisional entity in the spectrum of nonkeratinizing squamous cell carcinoma. This review addresses the major changes in the classification of sinonasal tract neoplasms in the new WHO classification.

SMARCB1 deficient sinonasal carcinoma: An emerging entity with a diagnostic challenge.

SMARCB1 deficient sinonasal carcinomas are rare neoplasms, classified under sinonasal undifferentiated carcinomas by the fourth edition of the World Health Organization (WHO) classification of head and neck tumors. It is characterized immunohistochemically by loss of SMARCB1(INI1) expression. We are reporting the case of a 63-year-old man who was evaluated for nasal stuffiness of 3 months duration in another hospital where a radiological evaluation showed a polypoidal soft tissue lesion in the right maxillary sinus extending to the right nasal cavity and spheno-ethmoidal sinus. He underwent excision biopsy which was reported as non- keratinizing nasopharyngeal carcinoma. He was referred to our center with residual disease in spheno-ethmoidal recess for which radiotherapy was given. After completion of radiotherapy, the primary site had no residual disease, but while on follow-up he developed left sided neck nodes within 4 months of completion of treatment. Excision of the lesion was done and histopathological and immunohistochemical analysis revealed it to be metastasis from SMARCB1 deficient sinonasal carcinoma and not nasopharyngeal carcinoma as diagnosed from the other center. This case is being reported to highlight the diagnostic challenge associated with this rare entity.

The contemporary management of cancers of the sinonasal tract in adults.

Sinonasal malignancies make up <5% of all head and neck neoplasms, with an incidence of 0.5-1.0 per 100,000. The outcome of these rare malignancies has been poor, whereas significant progress has been made in the management of other cancers. The objective of the current review was to describe the incidence, causes, presentation, diagnosis, treatment, and recent developments of malignancies of the sinonasal tract. The diagnoses covered in this review included sinonasal undifferentiated carcinoma, sinonasal adenocarcinoma, sinonasal squamous cell carcinoma, and esthesioneuroblastoma, which are exclusive to the sinonasal tract. In addition, the authors covered malignances that are likely to be encountered in the sinonasal tract-primary mucosal melanoma, NUT (nuclear protein of the testis) carcinoma, and extranodal natural killer cell/T-cell lymphoma. For the purpose of keeping this review as concise and focused as possible, sarcomas and malignancies that can be classified as salivary gland neoplasms were excluded.

IDH2 -Mutated Sinonasal Tumors: A Review.

INTRODUCTION: Genetic profiling has caused an explosion in the subclassification of sinonasal malignancies. Distinguishing several of these tumor types by histomorphology alone has been quite challenging, and although pathologic classification aims to be as specific as possible, it remains to be seen if this recent move toward tumor speciation bears clinical relevance, most particularly focused on subtyping for the sake of prognostication and treatment. One such recently described cohort, predominantly lumped under the moniker of sinonasal undifferentiated carcinoma (SNUC) is IDH2 -mutated sinonasal carcinoma, a high-grade carcinoma associated with mutations in the isocitrate dehydrogenase-2 ( IDH2 ) gene. A hotspot mutation in the R172 codon has been described in 50% to 80% of the tumors classified as SNUC, large cell neuroendocrine carcinomas, and rarely in cases classified as olfactory neuroblastoma. The use of immunohistochemical and molecular approaches is required to correctly identify this subset of sinonasal tumors, with further study necessary to elucidate their unique pathophysiology, ultimately determining whether a revision is required toward the current therapeutic approach. AIMS: Here, we provide an overview of the IDH2- mutated sinonasal tumors, discuss histopathologic and clinical features, and focus on molecular diagnostics and novel immunohistochemical markers. RESULTS: A review of the literature reveals 82 reported cases with IDH2 -mutated sinonasal tumors (IST), confirmed either by molecular studies or diagnostic immunohistochemical markers. The mean patient age is 60 years (female/male: 1/1.4), the median tumor size is 5 cm (range: 2.5 to 7.0 cm), and the most common location is the nasal cavity (81%). IST displays tumor necrosis and increased mitotes. Histopathologically, IST shows SNUC-like, large cell neuroendocrine carcinomas-like, or poorly differentiated carcinoma-like features (77%, 12%, and 9%, respectively). The molecular hotspot alterations in mitochondrial IDH2 are: R172S (61%), R172T (19%), R172G (7%), and R172M (3%). Sixty-five percent of tumors are surgically resectable, and all patients received chemotherapy, radiation therapy, or both. Rates of locoregional recurrence and distant metastasis are 60% and 40%, respectively. One-, 3- and 5-year survival rates are 83%, 50%, and 43%, respectively. In all but 1 study, IST is associated with better outcomes than IDH2 wild-type tumors and SMARCB1 -deficient sinonasal tumors.

Oral involvement of sinonasal undifferentiated carcinoma: A case report and immunohistochemical study of a challenging case.

INTRODUCTION: Sinonasal undifferentiated carcinoma (SNUC) is a rare tumor highly aggressive most frequently arise in the maxillary sinus and nasal cavity. Oral involvement is extremely rare. CASE REPORT: A 62-years-old male presents a large infiltrative mass involving the hard palate and left alveolar ridge. Computed tomography showed bone destruction and invasion of paranasal sinuses and orbits. Histology revealed a malignant neoplasm consisting of small round cells with minimal cytoplasm and hyperchromatic nuclei without any connection with the oral mucosal epithelium. Immunohistochemical analysis showed epithelial origin (CK-7+, CK-20+, AE1/AE3+, EMA+) and lacked strong evidence of squamous and neuroendocrine differentiation (p63-, 34ßE12-, NSE-/+, chromogranin-, synaptophysin-). TTF-1 negative ruled out the metastatic origin. A diagnosis of SNUC subtype positive for SMARCB1 (INI1) was reached. The patient was submitted to concurrent radiotherapy and chemotherapy without signs of recurrence after 2 years. CONCLUSION: SNUC involving the oral cavity is a rare malignancy that may mimic symptoms of dental infection or sinusitis. A careful correlation of clinical, microscopic, and immunohistochemical characteristics is mandatory for early diagnosis.

SMARCA4/BRG1-Deficient Sinonasal Carcinoma.

CONTEXT.­: Molecular analysis of poorly differentiated/undifferentiated sinonasal neoplasms has resulted in identification of a growing number of genetically defined tumors. SMARCA4-deficient sinonasal carcinoma is one such recently described entity that emerged from within sinonasal undifferentiated carcinoma (SNUC), neuroendocrine carcinoma (NEC), and teratocarcinosarcoma (TCS). OBJECTIVE.­: To identify SMARCA4-deficient sinonasal carcinomas from a large institutional cohort of poorly differentiated/undifferentiated carcinomas and evaluate their clinicopathologic features. DESIGN.­: SMARCA4/BRG1 immunohistochemistry was performed on all tumors diagnosed as SNUC, poorly differentiated carcinoma, NEC, and TCS during a 12-year period. SMARCA2/BRM and INSM1 immunostaining was performed in SMARCA4-deficient cases. RESULTS.­: Twelve SMARCA4-deficient sinonasal carcinomas were identified among 299 cases. Morphologically, 5 cases were large cell NEC, 2 cases were small cell NEC, and 5 were TCS. SMARCA4 loss was diffuse and complete in 10 cases, while 2 cases showed focal retention. Most cases showed diffuse cytokeratin staining accompanied by weak, usually focal staining for chromogranin and synaptophysin. INSM-1 showed negativity in most cases. All cases showed retained SMARCA2 expression. IDH1/2 mutation was absent in all cases analyzed. Four of 7 patients died of disease, and aggressive multimodality treatment provided better outcome. CONCLUSIONS.­: SMARCA4-deficient sinonasal carcinomas are morphologically akin to sinonasal poorly differentiated NECs and TCS, display cytokeratin positivity and only focal staining for neuroendocrine markers, and have aggressive biological behavior. Inclusion of SMARCA4 in the immunohistochemical panel for diagnostic workup of all sinonasal NEC and TCS phenotypes will facilitate their early recognition. Comprehensive germline and somatic mutational analyses of these tumors are necessary for further insights into their molecular pathogenesis.

Maxillary Sinus Floor Infiltration: Results From a Series of 118 Maxillary Sinus Cancers.

OBJECTIVES/HYPOTHESIS: Maxillary cancers are rare and aggressive tumors, which can spread beyond the sinus bony walls. Preoperative assessment of infiltration of maxillary sinus floor (MSF) is paramount for surgical planning, as palatomaxillary demolition significantly impacts patients' quality of life. This study investigates the challenges involved in the preoperative and intraoperative evaluation of MSF infiltration and analyzes its prognostic relevance. STUDY DESIGN: Retrospective case series. METHODS: A retrospective review of patients treated for sinonasal malignancies at a single Institution was performed. Patients receiving surgical-based treatment with curative intent for primary maxillary sinus cancers, between January 2000 and November 2019, were included. RESULTS: A cohort of 118 patients was analyzed. By comparing intraoperative findings (endoscopic assessment and frozen sections) with preoperative radiological assessment, diagnostic changes with regard to MSF infiltration were found in 27.1% (32/118 cases). MSF infiltration negatively affected the prognosis in both univariate and multivariate analyses in the overall population. In the subgroup of pT1-T3 tumors, MSF infiltration was significantly associated with reduced overall (P = .012), disease-free (P = .011), and distant recurrence-free (P = .002) survival rates. Conversely, pT classification was not able to stratify patients according to prognosis, mainly because early-staged cancers (pT1-T2) with MSF infiltration showed reduced survival rates, similar to those observed in pT3 cancers. CONCLUSIONS: Preoperative imaging should be integrated with intraoperative findings based on endoscopic inspection and frozen sections. Future studies are required to investigate the opportunity to incorporate MSF infiltration in the TNM staging system, considering its crucial role in defining the extent of surgery and its potential as prognosticator. LEVEL OF EVIDENCE: 4 Laryngoscope, 132:26-35, 2022.

SMARCB1(INI1)-deficient sinonasal adenocarcinoma: Report of a case previously diagnosed as high-grade non-intestinal-type sinonasal adenocarcinoma.

SMARCB1(INI1)-deficient sinonasal carcinoma is a recently recognized entity with wide histomorphologic spectrum. The classification of sinonasal adenocarcinoma (SNAC) is complex and yet to be redefined, especially the category of high-grade non-intestinal-type SNAC. Recently SMARCB1(INI1)-deficient SNACs with an unique oncocytoid/rhabdoid cytomorphology and variable degrees of glandular formation have been reported. Here we described a rare case of SMARCB1(INI1)-deficient SNAC composed of mainly oncocytoid/rhabdoid cells with mixed solid and cribriform patterns. This case was originally diagnosed as non-intestinal-type SNAC and was reclassified due to complete loss expression of SMARCB1(INI1) by immunohistochemistry (IHC). The SMARCB1(INI1) stain provides a valuable tool for identification of this specific type of SNAC. We compared this case with other SNACs diagnosed in our department and reviewed relevant literature for this specific type of SNAC.

Complete response to immunotherapy in sinonasal undifferentiated carcinoma.

Sinonasal undifferentiated carcinoma (SNUC) is an uncommon aggressive tumor. Locally advanced disease is usually diagnosed at presentation. Multidisciplinary approach is essential and aims to ensure optimal trimodal strategy. Induction chemotherapy is preferred in order to select patients who will benefit from chemoradiotherapy or surgery. Immunotherapy is not indicated in patients with recurrent SNUC. We describe an impressive response in a young man previously treated with radiotherapy and chemotherapy and demolitive surgery who had metastatic bone and lung disease. We also report data on PD-L1, next-generation sequencing, and neutrophil/platelets ratio.

[Therapeutic management and prognostic profile of a patient with maxillary sarcomatoid carcinoma (case report)]. / Carcinome sarcomatoïde: prise en charge thérapeutique et profil pronostique à propos d´une localisation maxillaire inhabituelle (à propos d´un cas).

Sarcomatoid carcinoma is a rare, aggressive, malignant tumor with a poor prognosis and a very high frequency of recurrence. Carcinoma of the maxillary sinus is extremely rare. We report the case of a 42-year-old woman with left maxillary process. Biopsy revealed aggressive sarcomatoid carcinoma with a lymph-node metastasis. The patient underwent surgical excision, lymph-node dissection followed by radiotherapy with good outcome. The rarity of this site-specific cancer poses a problem of diagnosis and timely management which is still a controversial topic. However, wide surgical excision is the gold standard treatment. This study highlights the anatomoclinical peculiarities and, in particular, the prognostic features of this tumor.

Clinical Implication of Diagnostic and Histopathologic Discrepancies in Sinonasal Malignancies.

OBJECTIVES: To evaluate the incidence of histopathologic diagnostic discrepancy for patients referred to our institution, identify pathologies susceptible to diagnostic error, and assess the impact on survival of histopathologic diagnostic discrepancies. METHODS: Three hundred ninety-seven patients with sinonasal cancers were identified, and discordance between the outside pathologic report and MD Anderson Cancer Center pathologic report was assessed. Overall survival and disease-specific survival were analyzed using Kaplan-Meier and log rank methods. RESULTS: Discordance of major histopathologic diagnoses was present in 24% (97 of 397) of reports, with sinonasal undifferentiated carcinoma, sarcoma, neuroendocrine carcinoma, and poorly differentiated carcinoma pathologies having the highest change in diagnosis (P < .01). A further 61% (244 of 397) had minor changes such as histologic grade, subtype, or stage, with sarcoma and neuroendocrine carcinoma pathologies being most susceptible to change (P < .02). Overall, the 5-year overall survival (OS) and disease-specific survival (DSS) was reduced in patients with a major change in histopathologic diagnosis (59.2% vs. 70.2% (P = .02) and 72.9% vs. 81.2% (P = .02), respectively). Furthermore, patients with a major change in diagnosis and prior treatment experienced a significant reduction in 5-year OS (61.9% vs. 70.4%, P = .03 < .01) and DSS (72.4% vs. 81.5%, P = .04). CONCLUSION: Histopathological diagnosis of sinonasal tumors is complex and challenging given the rarity of the disease. Obtaining the correct diagnosis is important for treatment selection and survival. In histologies prone to misdiagnoses, obtaining a second opinion from experienced head and neck pathologists at a high-volume institution may potentially lead to a change in treatment recommendations that could result in improved survival in patients with sinonasal malignancies. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:E1468-E1475, 2021.

Management of a Unique Sinonasal Undifferentiated Carcinoma Subtype in the Era of SARS-CoV-2.

The novel coronavirus (SARS-CoV-2) pandemic has influenced the timeliness of care for patients with both common and rare conditions, particularly those affecting high-risk operative sites such as the upper aerodigestive tract. Sinonasal undifferentiated carcinoma (SNUC) represents a rare malignancy of the sinonasal tract, a unique subset of which has never been previously reported in the otolaryngology literature and is characterized by inactivation of the SMARCB (INI-1) tumor suppressor gene. This subtype exhibits a particularly poor prognosis and is characterized pathologically by its rhabdoid appearance. Here we present the case of an individual who was diagnosed with a sinonasal mass during the SARS-CoV-2 pandemic, which was ultimately found to be SMARCB (INI-1)-deficient sinonasal carcinoma. Advanced imaging was deferred in the interest of limiting the patient's exposure to the virus, and expedited operative management was performed which facilitated prompt referral for adjuvant chemoradiation. The SARS-CoV-2 pandemic presents unique challenges, but the work-up of high-risk lesions must be prioritized; this continues to be paramount as SARS-CoV-2 resurges in many cities across the USA.

Undifferentiated nasopharyngeal cancer extending to maxillary sinus: a case report.

Undifferentiated nasopharyngeal cancer of the cavum (UCNT) is the most frequent neoplasm of the nasopharynx, having a close relationship with exposure to Epstein-Barr virus. It has a high potential for locoregional or distant invasion which are the cause of some treatment failures. The extension to the maxillary sinus is rarely described. We report here the case of a 38-year-old patient with headaches associated with epistaxis, left otalgia and facial pain. Examination by anterior rhinoscopy objectively revealed a polylobed ulcerating mass. Otoscopic examination revealed a left seromucous otitis media. Computed tomography showed a voluminous tumour process in the infra temporal fossa and nasopharynx with significant locoregional extension particularly in the maxillary sinus. Pathological examination revealed an UCNT of the cavum and the patient was classified as T4N2M0. The patient received chemoradiotherapy, with wide irradiation of the cervical lymph node areas. The deep localization of the cancer of the cavum, which is difficult to examine, requires a diagnostic and extension work-up, both endoscopic and radiological, which is an important step in the diagnostic and therapeutic management.

Osseous mass in a maxillary sinus of an adult male from the 16th-17th-century Spain: Differential diagnosis.

OBJECTIVE: To undertake a differential diagnosis of a large mass found in the left maxillary sinus of a cranium dated to the 16th-17th-century, and to expand knowledge of the diagnosis of osseous tissue formation in osteoarchaeological studies. MATERIAL: A cranium recovered from the cemetery of San Salvador de Palat de Rey church, León (Spain). METHODS: Macroscopic analysis, CT scanning. RESULTS: Macroscopic analysis indicated that the individual was probably a male over 30 years old with an ossified mass in the left maxillary sinus, measuring 24 × 19 × 24 mm, occupying approximately 27 % of the maxillary antrum. Computed tomography revealed a well-demarcated radiolucent unilocular mass with some radiopaque areas, with no communication with the alveoli of the premolars or molars. No erosive lesions or signs of inflammation were found. CONCLUSIONS: Neither the macroscopic, nor the radiological characteristics are compatible with inflammatory or malignant pathology, favoring a diagnosis of ossifying fibroma. SIGNIFICANCE: This case adds to the few reported cases in the osteoarchaeological literature, especially since there is limited relevant reference data to assist diagnosis. The CT scans and 3D reconstruction presented here facilitate differential diagnosis in future paleopathological studies. LIMITATIONS: Destructive methods were not authorized. SUGGESTIONS FOR FURTHER RESEARCH: In the future, micro-CT analysis, which was not performed in the current study, may add new and valuable information.

Sinonasal Undifferentiated Carcinoma (SNUC): From an Entity to Morphologic Pattern and Back Again-A Historical Perspective.

Since the first description of sinonasal undifferentiated carcinoma (SNUC) as a distinctive highly aggressive sinonasal neoplasm with probable origin from the sinonasal mucosa (Schneiderian epithelium), SNUC has been the subject of ongoing study and controversy. In particular, the SNUC category gradually became a "wastebasket" for any undifferentiated or unclassifiable sinonasal malignancy of definite or probable epithelial origin. However, with the availability of more specific and sensitive immunohistochemical antibodies and increasing implementation of novel genetic tools, the historical SNUC category became the subject of progressive subdivision leading to recognition of specific genetically defined, reproducible subtypes. These recently recognized entities are characterized by distinctive genetic aberrations including NUTM1-rearranged carcinoma (NUT carcinoma) and carcinomas associated with inactivation of different members of the SWI/SNF chromatin-remodeling gene complex such as SMARCB1-deficient and less frequently SMARCA4-deficient carcinoma. The ring became almost closed, with recent studies highlighting frequent oncogenic IDH2 mutations in the vast majority of histologically defined SNUCs, with a frequency of 82%. A review of these cases suggests the possibility that "true SNUC" probably represents a distinctive neoplastic disease entity, morphologically, phenotypically, and genetically. This review addresses this topic from a historical perspective, with a focus on recently recognized genetically defined subsets within the SNUC spectrum.

IDH2 Mutation Analysis in Undifferentiated and Poorly Differentiated Sinonasal Carcinomas for Diagnosis and Clinical Management.

A large number of tumor types arise from the mucosa of the sinonasal cavities. Although presenting clinically distinct behavior, due to poorly differentiated histologic features, they can be difficult to classify correctly. Our aim was to investigate whether IDH2 and IDH1 mutations may be specific to a subset of undifferentiated and poorly differentiated sinonasal carcinomas. A total of 125 tumor samples of 7 different histologic subtypes were analyzed for IDH mutations by sequencing and mutant-specific immunohistochemistry, and the results were correlated to clinical and follow-up data. The highest incidence of IDH2 mutations occurred in sinonasal undifferentiated carcinoma, with 11/36 (31%) cases affected. However, also, 1/9 neuroendocrine carcinomas, 2/4 high-grade non-intestinal-type adenocarcinomas, and 1/8 poorly differentiated squamous cell carcinomas carried the IDH2 mutation, whereas 1/48 intestinal-type adenocarcinomas harbored an IDH1 mutation. Immunohistochemical analysis of mutant IDH1/2 produced a number of false-negative results, but also 1 false-positive tumor was found. Disease-specific survival was more favorable in IDH2-mutant versus wild-type cases. Our data suggest that IDH-mutant sinonasal cancers, independent of their histologic subtype, may represent a distinct tumor entity with less aggressive clinical behavior. Clinically, patients with these mutations may benefit from specific IDH-guided therapies.

[Inverted papilloma: a study of 13 cases in the Oto-Rhino-Laryngology at the National University Hospital of Fann]. / Papillome inversé: à propos de 13 cas au Service d'Oto-Rhino-Laryngologie du Centre Hospitalier National Universitaire de Fann.

INTRODUCTION: Inverted Papilloma (IP) is a rare benign tumour of the nose and paranasal sinuses histologically characterized by invagination of the outer layer of the epithelium in the underlying chorion. Its most distinctive feature is a strong local aggressiveness, a tendency to recur and an unpredictable risk of association with epidermoid carcinoma. The purpose of this study was to report the epidemiological, clinical, paraclinical data as well as to assess the outcomes of endoscopic endonasal surgery. METHODS: We conducted a retrospective study on a series of 13 patients whose data were collected in the Oto-Rhino-Laryngology at the National University Hospital Center of Fann, from 1st January 2012 to 31st December 2017. All patients followed up for inverted papilloma confirmed by anathomopathological examination were included in the study. RESULTS: The average age of patients was 44 years, the sex-ratio was 2.25. All patients had nasal obstruction; 53% of them had rhinorrhea followed by epistaxis in 30% of cases. Right-sided symptoms were reported by 69% of patients, left-sided symptoms by 23% and bilateral symptoms by 7% of patients. Anterior rhinoscopy showed endonasal mass in all patients. All patients underwent CT scan; the MRI was performed in a single patient. Endoscopic resection of IP was performed in 10 patients (76.9%) while external approach was used in 23% of cases. Surgery helped to clarify where the tumor had originated: in 46% of cases in the maxillary sinus, in 15% in the lower nasal turbinate, in 15% in the mid-turbinate, in 7% in the ethmoid bulla and in 7% in the lateral wall of the nasal fossa. One patient had recurrence after an average period of 26 months. Malignant transformation to squamous cell carcinoma occurred in one patient. CONCLUSION: Inverted papilloma is a very aggressive tumor. CT scan is essential to highlight its spread, especially to bone. The advent of endoscopic surgery has revolutionised treatment, providing excellent results. But, there is nevertheless a risk of recurrence after surgery which motivates an indication for long term monitoring.

DNA methylation-based classification of sinonasal undifferentiated carcinoma.

Sinonasal undifferentiated carcinoma (SNUC) is an aggressive malignancy harboring IDH2 R172 mutations in >80% cases. We explored the potential of genome-wide DNA methylation profiling to elucidate tumor biology and improve the diagnosis of sinonasal undifferentiated carcinoma and its histologic mimics. Forty-two cases, including sinonasal undifferentiated, large cell neuroendocrine, small cell neuroendocrine, and SMARCB1-deficient carcinomas and olfactory neuroblastoma, were profiled by Illumina Infinium Methylation EPIC array interrogating >850,000 CpG sites. The data were analyzed using a custom bioinformatics pipeline. IDH2 mutation status was determined by the targeted exome sequencing (MSK-IMPACTTM) in most cases. H3K27 methylation level was assessed by the immunohistochemistry-based H-score. DNA methylation-based semi-supervised hierarchical clustering analysis segregated IDH2 mutants, mostly sinonasal undifferentiated (n = 10) and large cell neuroendocrine carcinomas (n = 4), from other sinonasal tumors, and formed a single cluster irrespective of the histologic type. t-distributed stochastic neighbor embedding dimensionality reduction analysis showed no overlap between IDH2 mutants, SMARCB1-deficient carcinoma and olfactory neuroblastoma. IDH2 mutants demonstrated a global methylation phenotype and an increase in repressive trimethylation of H3K27 in comparison to IDH2 wild-type tumors (p < 0.001). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed no difference in pathway activation between IDH2-mutated sinonasal undifferentiated and large cell neuroendocrine carcinomas. In comparison to SMARCB1-deficient, IDH2-mutated carcinomas were associated with better disease-free survival (p = 0.034) and lower propensity for lung metastasis (p = 0.002). ARID1A mutations were common in small cell neuroendocrine carcinoma but not among IDH2 mutants (3/3 versus 0/18 and p < 0.001). IDH2 mutations in sinonasal carcinomas induce a hypermethylator phenotype and define a molecular subgroup of tumors arising in this location. IDH2-mutated sinonasal undifferentiated carcinoma and large cell neuroendocrine carcinoma likely represent a phenotypic spectrum of the same entity, which is distinct from small cell neuroendocrine and SMARCB1-deficient sinonasal carcinomas. DNA methylation-based analysis of the sinonasal tumors has potential to improve the diagnostic accuracy and classification of tumors arising in this location.