Low-grade fibromyxoid sarcoma with heterotopic bone formation: case report and review of the literature

Introduction/Objective Low-grade fibromyxoid sarcoma (LGFMS) is an uncommon soft tissue malignancy with deceptively bland histologic appearance, and a tendency for late recurrence and metastasis. Cases with significant heterotopic ossification are rare. This presentation aims to characterize the features of LGFMSs showing heterotopic ossification reported in the literature, and further review the morphologic spectrum of this malignant neoplasm. Methods/Case Report We report the case of a 42-year-old male presenting with a 20-year history of a painless tumor in his left upper thigh. Computed tomography images showed coarse punctate peripheral calcifications, and the mass was resected. The tumor cells were immunohistochemically positive for MUC4, and positive for FUS (16p11.2) gene rearrangement by fluorescence in situ hybridization. Lamellar and woven bone with admixed adipose tissue was seen. Immunohistochemistry also showed focal weak to moderate staining for TLE-1. An English literature search using the terms “Evans tumor”, “low-grade fibromyxoid sarcoma”, “ossification”, “osseous metaplasia”, “bone metaplasia” and “bone formation” was performed. Nine cases were identified. The majority of subjects were males, with a mean age of 38 years (range of 12-61 years). The duration of symptoms before diagnosis ranged from a few months to 10 years. The tumor size ranged from 2.5 and to more than 12 cm. In a minority of subjects, calcifications were identified on imaging studies. Histologically, bone metaplasia was mainly seen at the periphery of the tumor. The majority of cases had a chromosomal translocation (FUS-CREB3L2 in 5 cases and EWSR1-CREB3L1 in one). Results (if a Case Study enter NA) NA Conclusion LGFMS is a tumor that can occur in a wide range of anatomical sites, and should be included in the differential diagnosis of any spindle cell neoplasm with hypocellular areas and bland cytology. Pathologists and clinicians should be aware of the rare possibility of heterotopic ossification in this tumor type, which can be radiologically detected as calcification and then confirmed histopathologically.