S-100 Immuno-Positive Low Grade Myofibroblastic Sarcoma of Nasal Cavity: A Rare Case Presentation and Review of Literature.

Introduction: Myofibroblastic neoplasms comprise a spectrum of benign/malignant neoplasms. Only low-grade malignant forms have been reproducibly characterized as a diagnostic entity in the WHO classification. Low grade myofibroblastic sarcoma (LGMFS) confined to the nasal cavity is extremely rare. Objective: To review previously reported cases of nasal cavity LGMFS and provide a better insight regarding its clinical and immunohistochemical features. Data synthesis: A review was performed involving two databases (PubMed and Google Scholar). Four cases of nasal cavity LGMFS were included. The lesion showed no gender or nasal-side predilection. All cases underwent wide excision. None showed distant metastasis while half recurred locally. Histologically, mitotic rate ranged from 1 to 3/10 high-power-field (HPF) and none exhibited spontaneous necrosis. Immuno-expression of calponin, smooth muscle actin (SMA) and vimentin were seen in either all four or three-fourth of cases. Diffuse S-100 expression was a unique finding in present case and not reported previously, that caused a diagnostic dilemma with schwannomas. Conclusion: LGMFS of nasal cavity is extremely rare. A wide resection is the primary treatment of choice. Adjuvant therapies (chemotherapy or radiotherapy) are of uncertain significance. Distant metastasis is rather unusual. Calponin, SMA and vimentin are highly sensitive immuno-markers. Diffuse S-100 expression is a possible finding. Mitotic rate < 6/10 HPF and absence of spontaneous necrosis are characteristic indolent features differentiating from high grade lesions. Trifecta of clinical and morphological features plus immunohistological phenotype, are sufficient for a definitive diagnosis. Electron microscopy is the most definitive confirmation test, however, should be reserved only for equivocal/atypical immunostaining pattern.