Myoepithelioma-like tumor of the vulvar region shows a quiet genome and heterogeneous detectable mechanisms of SMARCB1 inactivation: Integrated analysis of two cases and review of the literature.

Abstract

Myoepithelioma-like tumor of the vulvar region (MELTVR) is a rare SMARCB1-deficient mesenchymal neoplasm of adult women that can mimic malignant vulvar sarcomas, particularly epithelioid sarcoma. Although loss of SMARCB1/INI1 expression is a defining feature, the comprehensive genomic landscape of MELTVR remains poorly characterized. We report two cases of MELTVR and performed integrated histopathologic, immunophenotypic, and molecular analyses, including whole-exome sequencing (WES) with copy number assessment and targeted RNA-based fusion testing using the Archer FusionPlex Sarcoma panel. Histologically, both tumors consisted of relatively uniform epithelioid to short spindle cells in solid nests and cords within focal myxoid stroma, with complete loss of INI1 and positivity for smooth muscle markers and focal ER/EMA expression. Genomic profiling demonstrated a quiet molecular background in both cases, with low tumor mutation burden (0.45 and 1.03 mut/Mb) and no pathogenic SNVs/indels in major cancer-associated genes. One case showed a focal homozygous deletion of the SMARCB1 locus at 22q11.2, whereas the other case exhibited INI1 loss without detectable SMARCB1 mutation or copy number loss, suggesting heterogeneous mechanisms of inactivation. CDKN2A copy number remained neutral in both tumors. No canonical sarcoma-associated gene rearrangements, including EWSR1, FUS, PLAG1, or NR4A3, were identified. Together with a review of previously reported cases, these findings support MELTVR as an SMARCB1-inactivated neoplasm with low genomic complexity and highlight the diagnostic value of NGS-based profiling in excluding malignant mimics and preventing overtreatment.