LOW-GRADE MYOFIBROBLASTIC SARCOMA OF THE ORAL CAVITY

Abstract

Low-grade myofibroblastic sarcoma (LGMS) represents a distinct atypical myofibroblastic tumor of deep soft tissues, with a head and neck predilection. It has a variety of appearances, from fasciitis-like or fibromatosis-like to fibrosarcoma-like. Here, a series of four cases from two different institutions is shown, represented by 2 men and 2 women presenting a nodular lesion, with equal distribution in maxilla and mandibula. Microscopically, all cases showed neoplasms formed by oval to spindle cells in a fibrous stroma with myxoid and dense areas, some atypical mitoses, and prominent nucleoli. These findings suggested a mesenchymal tumor. An immunohistochemical panel was performed, which showed positivity for smooth muscle actin (3 of 4 cases), HHF35 (2 of 4 cases), β-catenin (3 of 3 cases), calponin (2 of 4 cases), and Ki-67 (range 5-40%). H-Caldesmon was negative for all cases, demonstrating myofibroblastic and smooth muscle differentiation. The diagnosis of LGMS was confirmed in all cases. Low-grade myofibroblastic sarcoma (LGMS) represents a distinct atypical myofibroblastic tumor of deep soft tissues, with a head and neck predilection. It has a variety of appearances, from fasciitis-like or fibromatosis-like to fibrosarcoma-like. Here, a series of four cases from two different institutions is shown, represented by 2 men and 2 women presenting a nodular lesion, with equal distribution in maxilla and mandibula. Microscopically, all cases showed neoplasms formed by oval to spindle cells in a fibrous stroma with myxoid and dense areas, some atypical mitoses, and prominent nucleoli. These findings suggested a mesenchymal tumor. An immunohistochemical panel was performed, which showed positivity for smooth muscle actin (3 of 4 cases), HHF35 (2 of 4 cases), β-catenin (3 of 3 cases), calponin (2 of 4 cases), and Ki-67 (range 5-40%). H-Caldesmon was negative for all cases, demonstrating myofibroblastic and smooth muscle differentiation. The diagnosis of LGMS was confirmed in all cases.