Switch/Sucrose Non-fermentable (SWI/SNF) Complex-Partial Loss in Sinonasal Squamous Cell Carcinoma. Impact in the Morphology and Prognosis

Sinonasal carcinomas are aggressive neoplasms that present a high morbidity and mortality rate with unfavorable prognosis. This group of tumors exhibits morphological and genetic diversity. Genetic and epigenetic alterations in these neoplasms are currently targets for diagnosis and treatment. The most common type of cancer originated in the sinonasal tract are sinonasal squa-mous cell carcinomas (SNSCC), which presents different histological patterns and variable his-tological aggressiveness. A significant number of alterations have been reported in sinonasal tu-mors, including deficiencies in the SwItch/Sucrose non-fermentable (SWI/SNF) chromatin remod-eling complex. In the sinonasal tract, deficiencies of the subunits SMARCB1/INI1, SMAR-CA4/BRG1 and SMARCA2 have been noted in carcinomas, adenocarcinomas, and soft tissue tu-mors with distinctive high-grade morphology and fatal prognosis. Objective: To identify the status of the SWI/SNF complex using immunohistochemistry in sinonasal squamous cell carci-nomas and its association with morphology and survival. Methods: A total of 1582 SNSCC cases were analyzed, selecting those with high-grade malignancy morphology, which were then evalu-ated immunohistochemically for SMARCB1 and SMARCA4 proteins. Their expression was compared with the biological behavior and survival of the patients. Results: Among the SNSCC, 47% corresponded to the non-keratinizing squamous cell carcinoma (NKSCC) type with high-grade characteristics, 40% were keratinizing squamous cell carcinomas (KSCC), 9% were SMARCB1-deficient carcinomas, and 4% were SMARCA4-deficient carcinomas. Mosaic expres-sion for SMARCB1 (NKSCC 33%, KSCC 21.9%) and SMARCA4 (NKSCC 14.6%, KSCC 12.2%) was identified, showing an impact on tumor size and progression. Conclusions: We identified that the mosaic expression of INI1 in NKSCC exhibited a worse prognosis compared to intact carcinomas and was similar to SMARCB1-deficent carcinoma.