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Biphenotypic Sinonasal Sarcoma With a Novel PAX3::MAML2 Fusion.
Mayu Uemura1, Anna Fong Na Goh1, Amit Kumar1
1Department of Pathology, Monash Health, Clayton, Victoria, Australia.
Genes, Chromosomes & Cancer
|July 3, 2026
Summary
This study reports the first case of biphenotypic sinonasal sarcoma (BSNS) with a novel PAX3::MAML2 gene fusion. This finding expands the known genetic landscape of BSNS and related head and neck tumors.
Area of Science:
- Oncology
- Genetics
- Pathology
Background:
- Biphenotypic sinonasal sarcoma (BSNS) is a rare, low-grade spindle cell neoplasm.
- BSNS typically exhibits dual neural and myogenic differentiation, often involving PAX3 gene fusions, with MAML3 as a common partner.
Purpose of the Study:
- To report the first case of BSNS with a novel PAX3::MAML2 fusion.
- To characterize the clinicopathological and molecular features of this unique BSNS presentation.
Main Methods:
- Histopathological examination of tumor morphology and immunohistochemical staining.
- RNA sequencing to identify gene fusions.
Main Results:
- A polypoid lesion from the left ethmoid of a 61-year-old male was diagnosed as BSNS.
- Tumor cells showed bland spindle morphology, fascicular and whorled patterns, and co-expressed S100 and smooth muscle actin.
- RNA sequencing revealed a novel PAX3::MAML2 fusion transcript.
Conclusions:
- This case represents the first documented instance of BSNS with a PAX3::MAML2 fusion.
- The findings underscore the importance of comprehensive fusion testing in BSNS and highlight the expanding spectrum of gene fusions in sinonasal neoplasms.
