Low-grade myofibroblastic sarcoma

Low-grade myofibroblastic sarcoma (LGMS) is a subtype of the malignant sarcomas. As it is currently recognized, LGMS was first described as a rare, atypical myofibroblastic tumor (i.e. a tumor consisting of cells with the microscopic features of fibroblasts and smooth muscle cells) by Mentzel et al. in 1998. Myofibroblastic sarcomas had been divided into low-grade myofibroblastic sarcomas, intermediate‐grade myofibroblasic sarcomas, i.e. IGMS, and high‐grade myofibroblasic sarcomas, i.e. HGMS (also termed undifferentiated pleomorphic sarcoma and pleomorphic myofibrosarcoma [and formerly termed malignant fibrous histiocytoma]) based on their microscopic morphological, immunophenotypic, and malignancy features. LGMS and IGMS are now classified together by the World Health Organization (WHO), 2020, in the category of intermediate (rarely metastasizing) fibroblastic and myofibroblastic tumors. WHO, 2020, classifies HGMS (preferred name: undifferentiated pleomorphic sarcoma) as a soft tissue tumor in the category of tumors of uncertain differentiation. This article follows the WHO classification: here, LGMS includes IGMS but not HGMS which is a more aggressive and metastasizing tumor than LGMS and consists of cells of uncertain origin.

LGMS tumors are typically painless lesions that develop in: 1) the subcutaneous tissues, i.e. the lowermost layer of the skin; 2) submucosa, i.e. the thin layer of tissue lying just below the mucous membranes that line passageways such as the gastrointestinal, respiratory, genitourinary tracts; 3) muscles; and 4) bones. They most often develop in middle-aged adults (average: 40 years old) but have been diagnosed in all age-groups. These tumors often recur at the sites of their surgical removal and may metastasize to nearby lymph nodes and distant tissues.

LGMS's are commonly treated by surgical removal of the tumor along with all its cells, which if not removed increase the probability that the tumor will recur at the site of its removal. LGMS tumors typically show little or no sensitivity to radiotherapy and chemotherapy treatments.