A 75-year-old female underwent a detailed examination for pancytopenia at her previous medicine. Contrast CT revealed a 5 × 3 × 3.3 cm tumor with imaging effect on the internal side of the mass in the right erector spinal muscle. The patient was referred to the orthopedic department in Shimane university hospital for further examination. MRI revealed high density in the T1-contrast weighted images (WIs) (A, B) and iso and multifocal high density in the T2-WIs (C). In the fat suppression T2-WIs, high-density area was recognized inside the tumor (D). FNA was performed under ultrasound guidance and a malignant tumor was detected. Subsequently, tumor resection was performed. As for pancytopenia, it was the diagnosis of myelodysplastic syndrome by the subsequent bone marrow examination. Most of the tumor cells are isolated and composed of eccentrically located nuclei and an oxyphilic cytoplasm. Nuclei have fine chromatin and unclear nucleoli. Abundant cytoplasm somewhat resembles Golgi apparatus. Sometimes binuclear tumor cells were observed. There are regions of different density of tumor cells (A). The tumor cells have an eccentric and eosinophilic cytoplasm (B), with no increase in mitosis (C). In low-density area, abundant and weakly eosinophilic stroma can be seen (D). Immunohistochemistry revealed tumor cells that were diffusely positive for vimentin (E) and MUC4 (F), focally and weekly positive for CD99, and negative for AE1/AE3, CAM5.2, Myeloperoxidase, CD138, LCA, Myogenin, Desmin, αSMA, MyoD1, CD31, CD34, WT-1, ERG, D2-40, MDM2, c-kit, S100, HMB45, Melan A, and Mib-1 index is 3%. The surface color of the tumor was white and the boundary between the surrounding muscle and the tumor surface was relatively well-defined despite absence of a tumor capsule (A). Even in the surgical specimen, regions with non-sclerotic high density of tumor cells (B) and sclerotic low density of tumor cells (C) were observed. In the Sclerosing area, corded growth of epithelioid cells within a densely sclerotic stroma, which is a typical feature of SEF, was also observed (D). EWSR1 break-assay FISH (EWSR1 Breakapart kit, Cytocell Ltd, Cambridge), and EWSR1-CREB3L1, EWSR1-CREB3L2 fusion FISH (EWSR1:RP11-305J10, CREB3L1:RP11-1106J11, CREB3L2: RP-11-377B19) were performed on interphase nuclei from paraffin-embedded sections. We detected break-apart signals of EWSR1 (E) but, could not detect fusion signals of EWSR1-CREB3L1 or EWSR1-CREB3L2 (data not shown). We also performed FUS-CREB3L1, FUS-CREB3L2 fusion assays (FUS: RP11-157F22), neither of these fusion genes was detected.