Malignant brain tumor in an infant showing histopathological features of yolk sac tumor but genetic and epigenetic features of AT/RT

Underreporting of SMARCB1 alteration by clinical sequencing: Integrative patho-genomic analysis captured SMARCB1/INI-1 deficiency in a vulvar yolk sac tumor

•SMARCB1/INI1-deficient gynecologic tumors are rare and clinically aggressive. A subset shows primitive yolk sac tumor features.•Due to technical limitation of next generation sequencing (NGS) and interlaboratory variability in sequencing methodologies and analytical pipelines, SMARCB1 deficiency caused by somatic copy number variations (SCNV) may be underreported by NGS.•To improve identification of SMARCB1/INI1-deficient neoplasm, we propose the following strategy: First, careful pathology slide review and detection of rhabdoid cells should raise the possibility of SMARCB1/INI1 deficiency. Second, INI1 IHC is a useful complementary test to exclude clinical suspicion of SMARCB1 deficiency in the context of negative molecular reporting. Third, knowledge of potential underreporting of SMARCB1 mutation would avoid underdiagnosis.

SWI/SNF-deficient Sinonasal Carcinomas

The classification of poorly differentiated sinonasal carcinomas and their nonepithelial mimics has experienced tremendous developments during the last 2 decades. These recent developments paved the way for an increasingly adopted approach to a molecular-based or etiology-based refined classification of the many carcinoma variants that have been historically lumped into the sinonasal undifferentiated carcinoma category. Among these new achievements, recognition of carcinoma subtypes driven by defects in the Switch/Sucrose nonfermentable (SWI/SNF) chromatin remodeling complex represents a major highlight. This resulted in a new definition of 4 sinonasal entities driven solely or predominantly by Switch/Sucrose nonfermentable complex deficiency: (1) SMARCB1(INI1)-deficient sinonasal carcinoma (lacking gland formation and frequently displaying a non-descript basaloid, and less frequently eosinophilic/oncocytoid morphology, but no features of other definable subtypes), (2) SMARCB1-deficient sinonasal adenocarcinoma (with unequivocal glands or yolk sac-like pattern), (3) SMARCA4-deficient undifferentiated (sinonasal undifferentiated carcinoma-like) carcinoma (lacking glandular or squamous immunophenotypes), and (4) SMARCA4-deficient subset (~80%) of sinonasal teratocarcinosarcoma. Fortunately, diagnostic loss of all these proteins can be detected by routine immunohistochemistry, so that genetic testing is not mandatory in routine practice. This review summarizes the main demographic, clinicopathological, and molecular features of these new entities.