Biphenotypic sinonasal sarcoma - a case report.

BACKGROUND: Biphenotypic sinonasal sarcoma (BFSS) is a topographically specific low-grade sarcoma that was first described only 10 years ago. The term biphenotypic comes from the co-expression of markers of muscle differentiation and neural crest that is characteristic for this tumor. CASE: A 78-year-old woman manifested with prolonged breathing difficulties through the left nasal passage. Rhinoendoscopy and CT scans showed an obturation of the middle and posterior part of the left nasal cavity by a polypoid tumor mass with a stalk in the ethmoid sinus. It spread into the nasopharynx. The tumor was resected and extracted from the nasopharynx through the oral cavity. Grossly, it was a compact polyp measuring 6 × 3,5 × 3cm. Histology revealed a uniform neoplastic spindle cell population arranged in a fascicular pattern. It expres-sed S100 protein, smooth muscle actin, calponin and muscle-specific actin. Molecular genetic analysis of the tissue showed PAX3:: MAML3 gene fusion. The findings confirmed a dia-gnosis of BFSS. CONCLUSION: BFSS is a very rare, locally aggressive malignant tumor without metastatic potential. In contrast to other malignancies in a given locality, it possesses a relatively favorable prognosis. In bio-psy practice, the pathologists knowledge of this unique histopathological entity is principal because it should be always considered when encountering a low-grade spindle cell neoplasia arising in the sinonasal region.