Biphenotypic Sinonasal Sarcoma: A Series of Six Cases with Evaluation of the Clinicopathological Characteristics and Prognosis

Introduction: The biphenotypic sinonasal sarcoma (BSS) is the mesenchymal origin with a low histological grade of malignancy, mainly affecting the sinus cavity and middle-aged individuals with a female predilection. Currently, molecular mutations, clinical behavior, morphology and immunohistochemical findings are well defined. We report a review of six clinical cases diagnosed with SBS.

Materials and Methods: Six cases, previously diagnosed as BSS during 2005 to 2017, were selected and retrieved from our archives, two of them were previously diagnosed as sarcomas of low histological grade of malignancy. The medical record and imaging data were collected, besides the histological slides (hematoxylin and eosin staining). Using antibodies directed against the following antigens: Protein S-100, Caldesmon, Smooth muscle actin, MyoD1, Myogenin, CD34 and Cytokeratins AE1/AE3. The immunohistochemical staining was classified as “negative,” “focal positive,” or “diffuse positive.”

Results: The six cases had an age range between 29 and 60 years, with female preference (83.4%). The localization os de tumors was in the nasal cavity in 4 cases (66,7%), temporal bone in 1 case (16.4%) and hard palate / maxillary sinus in 1 case (16.4%). Four cases presented partial nasal obstruction, epistaxis and recurrent rhinosinusitis. The CT scan of BSS located in hard palate/maxillary sinus ([Fig. 1]) and in [Fig. 2] there is a view of the surgical resection of the same case. All had density of soft tissue lesions without hemorrhage and necrosis. All six patients underwent extensive surgical resection. Only one case presented metastasis and dedifferentiation to sarcoma of high histological grade of malignancy. Six cases presented an infiltrative pattern, not encapsulated, with bone invasion, hypercellular and paucicellular areas, in the middle with benign glandular hyperplasia ([Fig. 3]). The type of vessels was hemangiopericytoma absent necrosis. The tumor cells were monotonous and organized into fascicular and storiform patterns. The cytoplasm was sparse and eosinophilic and mitotic figures were rare, generally less than 2 per large growth field. Finally, the cell population showed a biphasic staining pattern. In all cases, cytoplasmic β-catenin, muscle-specific actin, smooth muscle actin and S100 were positive ([Figs. 4] and [5]). On the other hand, desmin, MyoD1, and myogenin were focal positive in 3 cases and AE1/AE3 was negative.

Discussion: BSS is an entity recently described and presenting a peculiar clinical course, histopathology findings and known genetic background. Histologically, it shows similarity with other sarcomas of the sinonasal tract. Therefore, it is important to consider the differential diagnosis of this entity. A correctly selected immunohistochemical exam is useful for identifying and differentiating BSS from other fusiform cell lesions of the sinonasal tract.