Left Facial Primary Leiomyosarcoma Misdiagnosed as Atypical Fibroxanthoma and Immunochemical Markers Relevant to Diagnosis: A Case Report

Abstract

Soft tissue sarcomas are relatively rare neoplasms of mesenchymal origin that generally make up less than 2% of all adult malignant neoplasms. Atypical fibroxanthoma is a benign soft tissue tumor often confused with malignant variants of similar tumors such as leiomyosarcoma due to similar staining markers and cell morphology. We report a case of a 70-year-old caucasian male who initially presented with a 2 cm exophytic left facial lesion that was misdiagnosed as atypical fibroxanthoma upon biopsy. The patient underwent a wide local excision of the growing 11 cm mass and immediate reconstruction with a cervicofacial flap and full thickness skin graft. Pathological analysis of the specimen revealed the final diagnosis as confirmed primary leiomyosarcoma. Both the patient’s biopsy report and the surgical pathology report revealed similar negative findings (desmin, cytokeratin AE1/AE3, p63, SOX10) as well as similar positive findings (smooth muscle actin and CD68). Critical distinctions that led to a change in diagnosis from atypical fibroxanthoma to leiomyosarcoma emerged during the final pathological analysis, which revealed more widespread positive staining for smooth muscle actin and muscle-specific actin throughout the surgical specimen along with detailed cell and nucleus morphology of atypical spindle cells in the dermis and subcutis. This valuable information was not available during the initial biopsy when the lesion was smaller. It is possible that earlier diagnosis of primary leiomyosarcoma could have resulted in advanced pre-operative treatment and excision of the facial lesion, preventing involvement of surrounding areas such as the patient’s left eye, ear, and facial nerve.