Low-Grade Myofibroblastic Sarcoma of the Oral and Maxillofacial Region: An International Clinicopathologic Study of 13 Cases and Literature Review

Abstract

Low-grade myofibroblastic sarcoma (LGMS) represents an atypical tumor composed of myofibroblasts with a variety of histological patterns and with a high tendency to local recurrence and a low probability of distant metastases. LGMS has predilection for the head and neck regions, especially the oral cavity. This study aimed to report 13 new cases of LGMS arising in the oral and maxillofacial region. This study included LGMS cases from five oral and maxillofacial pathology laboratories in four different countries (Brazil, Peru, Guatemala, and South Africa). Their clinical, radiographic, histopathological, and immunohistochemical findings were evaluated. In this current international case series, most patients were females with a mean age of 38.7 years, and commonly presenting a nodular lesion in maxilla. Microscopically, all cases showed a neoplasm formed by oval to spindle cells in a fibrous stroma with myxoid and dense areas, some atypical mitoses, and prominent nucleoli. The immunohistochemical panel showed positivity for smooth muscle actin (12 of 13 cases), HHF35 (2 of 4 cases), β-catenin (3 of 5 cases), desmin (3 of 11 cases), and Ki-67 (range from 5 to 50%). H-caldesmon was negative for all cases. The diagnosis of LGMS was confirmed in all cases. LGMS shows predominance in young adults, with a slight predilection for the female sex, and maxillary region. LGMS should be a differential diagnosis of myofibroblastic lesions that show a proliferation of spindle cells in a fibrous stroma with myxoid and dense areas and some atypical mitoses, supporting the diagnosis with a complementary immunohistochemical study. Complete surgical excision with clear margins is the treatment of choice. However, long-term follow-up information is required before definitive conclusions can be drawn regarding the incidence of recurrence and the possibility of metastasis.

Keywords: Fusocellular neoplasia; Immunohistochemistry; Low-grade myofibroblastic sarcoma; Oral cavity; Oral pathology.

Fig. 1

Extraoral and Intraoral clinical images of low-grade myofibroblastic sarcoma. A slight increase in volume is observed in the right maxilla region after 4 months duration (A). Patient with an expansive lesion in the right face of 5 months duration (B). Tumor located in the right posterior maxilla, presenting extensive areas of necrosis and ulceration (C). Large tumor located in right posterior maxilla, after biopsy, the lesion showed an expansive growth, involving the airways (D)

Fig. 2

Radiographic features of low-grade myofibroblastic sarcoma. Computed tomography (A) and panoramic (B) images demonstrating large, expansive, destructive, radiolucent lesions of the right maxilla in two different patients. Periapical radiograph showing a mixed radiolucent–radiopaque lesion of the left mandible with an ill-defined appearance (C)

Fig. 3

Histopathological characteristics of low-grade myofibroblastic sarcoma. Neoplasia presenting ulcerative surface (H&E, × 10) (A) with proliferation of spindle cells arranged in a storiform pattern in a dense fibrous stroma (H&E, × 10) (B) and some areas of loose connective tissue (H&E, × 20) (C). Infiltration of cells between and around muscle fibers producing a checkerboard-like appearance (H&E, × 40) (D). It also observes the presence of figures of mitosis and prominent nucleoli (H&E, × 40) (E). Areas of fibromyxoid stroma (H&E, × 40) (F)

Fig. 4

Immunohistochemical characteristics of low-grade myofibroblastic sarcoma. SMA shows tram-track staining (12 out of 13 cases) (A), focal expression of HHF35 (2 of 4 cases) (B), strong nuclear β-catenin immunopositivity (3 of 5 cases) (C), calponin positivity of tumor cells (2 of 4) (D), vimentin showed diffuse cytoplasmic positivity in tumor cells (4 of 4 cases) (E) and Ki-67 (range 5–50%) (F). H-caldesmon was negative in all thirteen cases