With a preoperative diagnosis of primary malignant liver tumor of unknown origin with invasion of the IVC and possibly intrahepatic metastasis, laparotomy was performed. The huge tumor, which was located mainly in the liver, adhered to the diaphragm, right lower lobe of the lung, and pericardium. The tumor also adhered to the suprahepatic IVC. By using the total hepatic vascular exclusion technique (THVE), extended left hepatectomy with resection of the caudate lobe of the liver was performed. The diaphragm, the right lower lobe of the lung, and the pericardium were resected. Next, after clamping the suprahepatic IVC below the right atrium and the retrohepatic IVC above the renal veins, the adhered IVC wall was removed together with the liver. The resected IVC wall was replaced with an expanded polytetrafluoroethylene graft. Since the tumor in segment 8 was suspicious of intrahepatic metastasis, partial hepatectomy of segment 8 was also performed. No other liver tumors were found during surgery.

A macroscopic view of the resected tumor was shown in Figure ​Figure2.2. The tumor, measuring 68 mm × 54 mm, was mainly located in segment 1 of the liver. Microscopically, the tumor mainly existed in the liver with invasion into neighboring extrahepatic soft tissue including the wall of the IVC and diaphragm. Moreover, tumor thrombi were identified in the left portal vein and its branches. The tumor consisted of uniformly round or polygonal epithelioid cells with a faintly eosinophilic cytoplasm (Figure ​(Figure3A3A and ​andB).B). The tumor cells were arranged in strands, nests, cords or sheets and embedded in a heavily hyalinized matrix. The microscopic findings of the tumor in segment 8 were similar to those of the primary tumor, and that tumor was diagnosed as an intrahepatic metastasis. Immunohistochemical staining of the main tumor was positive for vimentin (Dakopatts, Glostrup, Denmark), bcl-2 (Dakopatts), and CD99 (Dakopatts), and was negative for AE1/AE3 (Dakopatts), CAM5.2 (Becton Dickinson, San Jose, CA), desmin (Dakopatts), epithelial membrane antigen (EMA) (Dakopatts), CD34 (Nichirei, Tokyo, Japan), S100, α-smooth muscle actin (α-SMA) (Dakopatts), neuron-specific enolase (Dakopatts), CD56 (Dakopatts), leukocyte common antigen (LCA) (Dakopatts), CD30 (Dakopatts), HMB45 (Dakopatts), AFP (Dakopatts), and CA19-9 (Zymed Laboratories Inc., San Francisco, CA) (Figure ​(Figure3C).3C). The MIB-1 labeling index (Dakopatts) was 30%. Moreover, cytogenetic analysis did not show t (X; 18) chromosomal translocation, which is frequently observed in synovial sarcoma[^12,13]. Based on the results of histopathological examination, cytogenetic analysis, and immunohistochemical patterns, the tumor was finally diagnosed as SEF. Although the tumor was associated with invasion to the wall of the IVC and diaphragm, the most part of the tumor existed in segment 1 of the liver. Moreover, tumor thrombi were identified in the right portal vein and its peripheral branches, and intrahepatic metastases, which were frequently seen in the primary liver malignant tumor. Therefore, the SEF probably originated from the liver. The resection margins were free of tumor. The noncancerous area of the liver was histologically normal. The patient had an uneventful postoperative course and was discharged from the hospital 24 d after surgery.

Seven months after surgery, the patient complained of back pain. CT examination showed recurrent SEF in the extrahepatic retroperitoneal tissue (Figure ​(Figure1C1C and ​andD).D). Systemic chemotherapy consisting of adriamycin and ifosfamide was applied. Close follow-up showed arrest of tumor growth and no new metastatic lesions within the first 3 mo. Subsequently, laparotomy was performed for the excision of the recurrent tumor 12 mo after the initial surgery. The recurrent tumor, located in the retroperitoneal tissue and adherent to the remnant liver, also infiltrated the graft IVC. Using the THVE approach, the tumor was resected with the adherent liver tissue and the infiltrated IVC graft. The resected IVC was again replaced with an expanded polytetrafluoroethylene graft. The microscopic findings of the resected tumor were similar to those of the primary SEF. The immunohistochemical staining patterns of the primary tumor and the recurrent tumor were also similar. The patient had an uneventful postoperative course and was discharged from the hospital 30 d after the surgery.

The histopathological differential diagnosis of SEF generally includes a wide variety of tumors with sclerotic or epithelioid features, and thus immunohistochemical analysis is essential for precise diagnosis of SEF. In the present case, differential diagnosis was challenging for the following reasons. Undifferentiated hepatocellular carcinoma and infiltrating adenocarcinoma should be differentiated from SEF, but immunohistochemical staining for AFP, CAM5.2, and AE1/AE3 was negative in the present case. Synovial sarcoma should also be differentiated from SEF. Cytogenetic identification of t (X: 18), which is found in synovial sarcoma, could differentiate synovial sarcoma from SEF[^12,13]. No chromosomal translocation was observed in the present case. Furthermore, smooth muscle neoplasms, such as hyalinized leiomyoma or leiomyosarcoma, frequently resemble SEF histopathologically, but they are characterized by immunohistochemical positivity for α-SMA and desmin. Clear cell sarcoma and malignant peripheral nerve sheath tumors may need to be distinguished from SEF. However, these tumors are positive for S100 immunostaining. Moreover, sclerosing lymphoma and malignant melanoma of the soft part are also on the list of differential diagnoses, but these tumors are usually positive for LCA and HMB45, respectively, and were negative in our case. Epithelioid hemangioendothelioma could be ruled out based on immunonegativity for CD34, and alveolar rhabdomyosarcoma could be excluded by the negative result of desmin and absence of rhabdomyoblasts. Moreover, absence of osteroid formation excluded traosseous osteosarcoma in the present case. Thus, taking into consideration not only the histopathological findings but also the results of cytogenetic analysis and immunohistochemical examinations, the tumor was finally diagnosed as SEF.

In reviewing previous reports, SEFs usually arise in the deep soft tissue and are frequently associated with the adjacent fascia or periosteum. Most SEFs are located in the lower extremities and limb girdles, followed by the trunk, upper extremities, and the head and neck area[^1-10].

In this case, although the tumor was associated with invasion to the wall of IVC and diaphragm, the most part of the tumor existed in the liver. Moreover, in this case, tumor thrombi and intrahepatic metastases were concurrently identified. These features might suggest that the tumor had originated in the liver. To our knowledge, there have been no reports of SEF originating from the liver.

The etiology of most malignant soft tissue tumors, including SEF, is generally unknown. A recent report reviewed 90 patients with SEF and found no significant gender difference with a mean patient age of 47 years (range, 14-87 years)[⁵]. The average tumor size at diagnosis is about 8 cm. Several investigators reported previously the association between radiation and occurrence of fibrosarcoma, though our patient had no history of radiation[⁹9,¹⁴14].

The established treatment for SEF is complete resection. There is no evidence to support the effect of chemotherapy and/or radiotherapy, though these therapies were used in some previous reports[^3,10]. As for prognosis, Chow et al[⁴] reported 57 patients with SEF with a local recurrence rate of 48%, metastasis rate of 60%, and mortality rate of 35%. Moreover, in a study of 16 patients with SEF by Antonescu et al[³], the local recurrence rate, metastasis rate, and mortality rate were 50%, 86% and 57%, respectively[⁵]. Distant metastasis is reported to be most common in the lung, followed by bone, soft tissue, brain, and lymph nodes[^1-5]. These previous reports of poor prognosis suggest that SEF is a clinicopathologically distinct soft tissue tumor with malignant potential although it is categorized as a low-grade neoplasm in the sarcoma group.