低级别肌成纤维瘤样肉瘤（LGMS）是一种由具有多种组织学模式的肌成纤维细胞组成的非典型肿瘤，具有高复发倾向和低远处转移的可能性。LGMS主要发生在头颈部，尤其是口腔。本研究旨在报告13例新发生于口腔颌面部的LGMS病例。本研究收集了来自巴西、秘鲁、危地马拉和南非四个国家的五个口腔颌面病理学实验室的LGMS病例。研究对其临床、影像学、组织病理学和免疫组化学结果进行了评估。在当前的这个国际病例系列中，大多数患者为女性，平均年龄为38.7岁，通常表现为上颌部的结节病变。镜下观察显示，所有病例均显示为由椭圆形至梭形细胞形成的肿瘤，其中包含有黏液样和密集区域的纤维组织，一些非典型有丝分裂和显著的核仁。免疫组化学检测显示，平滑肌动蛋白（13例中的12例）、HHF35（4例中的2例）、β-连环素（5例中的3例）、desmin（11例中的3例）和Ki-67（范围从5%到50%）呈阳性。对于所有病例，H-蔑胺呈阴性。所有病例均诊断为LGMS。LGMS主要发生在年轻成年人中，轻微偏好女性和上颌区域。LGMS应是肌成纤维细胞瘤样病变的鉴别诊断，该病变表现为纤维组织中梭形细胞增生和黏液样和密集区域，伴有一些非典型有丝分裂，可通过辅助免疫组化学研究支持诊断。完全切除术是治疗的首选。然而，在得出关于复发率和转移可能性的明确结论之前，需要进行长期随访。© 2023作者，独家许可给施普林格科学+商业媒体有限责任公司，属施普林格自然集团的一部分。

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.© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.