Synovial sarcoma is the third most common histological type of soft tissue sarcoma of the extremities, which mainly affects adolescents and young adults [4
]. It is slightly more common in men than in women, with a male-to-female ratio of 3:2 [5
]. Despite its name, synovial sarcoma does not originate from synovial tissue, but from multipotent stem cells that differentiate into mesenchymal and/or epithelial structures [6
]. It is characterized by a unique t(X;18)(p11;q11) chromosomal translocation, which leads to the formation of the SS18-SSX fusion gene [7
]. Currently, the best treatment for synovial sarcoma remains undefined, and complete surgical excision of the tumor mass followed by adjuvant radiotherapy and/or chemotherapy is the preferred current choice [8
Synovial sarcoma often has no specific clinical presentations that distinguish it from other sarcomas. Typically, it presents as a slowly enlarging, deep-seated mass, which is sometimes slightly painful. It is often misdiagnosed as a benign lesion, and simple excision is performed without adequate pre-surgical evaluation. In particular, as the majority of subcutaneous soft-tissue lesions are benign or inflammatory, simple excision is often performed without a biopsy by physicians and surgeons who do not have specific training in oncology [9
]. As a result, some aggressive tumors, including synovial sarcoma, can recur within years. Therefore, an early diagnosis is extremely important for the successful treatment of soft tissue synovial sarcoma. Subcutaneous sarcomas have been reported to account for approximately 30
% of all soft tissue sarcomas [9
]. In our case, the first clinical sign of synovial sarcoma was a slightly painful subcutaneous mass, and the mass was excised simply. The poor outcome of our patient further stresses the importance of adequate pre-surgical evaluation and post-surgical pathological analysis in the management of a subcutaneous mass.
Although synovial sarcomas are a high-grade soft tissue malignancy, most are characterized by slow growth. The mass may be present for an extended period before presentation and rapid spread and early deaths are seen only occasionally. In the present case, the disease progressed rapidly and the patient died within 4
months of symptom recognition. Given the small tumor size at presentation and the subsequent rapid disease progression, we surmise that local invasion and lymph node metastasis was likely to have occurred before the initial local excision of the mass. Therefore, a wide excision plus adjuvant radiotherapy and/or chemotherapy could have been performed. In addition, for the local excision of a subcutaneous tumor, violation of the underlying fascia may facilitate tumor local invasion, as the fascia provides an excellent deep barrier to tumor spread [9
]. Overall, benign tumors should be treated with a marginal excision, whereas malignant tumors should be widely excised. It is important to obtain adequate ablative margins and prevent local recurrence in patients with synovial sarcoma [10
The development of a non-healing wound that does not respond to conventional antibiotic therapy and local wound care is another interesting point of our case. Although cancer has been identified to be a common cause of non-healing wounds [11
], there have been very few reports of patients with synovial sarcoma who developed a non-healing wound. Several reasons may explain the development of a non-healing wound in our patient. Firstly, the sarcoma itself can give rise to wounds. Secondly, severe edema can slow the rate of healing, as dehydration adversely affects optimum wound healing by disturbing cellular metabolism and reducing circulatory blood volume [11
]. Finally, malnutrition may delay wound healing, as adequate nutrition is essential for effective wound healing [11
]. Interestingly, a recent report demonstrated that a postoperative non-healing wound that did not respond to conventional therapy was treated successfully with the local application of 3% citric acid ointment for 25
days in a patient with synovial sarcoma of the knee [13
MRI is the preferred imaging modality for the evaluation of soft tissue sarcomas because of its excellent tissue contrast and ability to depict the lesion in multiple planes. It is not only useful for evaluating the extent of the tumor and its involvement of adjacent soft-tissue structures, but also for differentiating tumor from muscle tissue and depicting the involvement of neurovascular structures, tendons, fascial/fat planes and bone marrow. On MR images, lesion margins of synovial sarcomas are well defined in 53 to 91% of cases and poorly defined in 9 to 47% [14
]. In our case, the lesion was irregular and poorly confined, which was perhaps due to the fact that MRI was performed after local excision and local invasion had occurred. Therefore, preoperative MRI investigations might be more useful for making an early diagnosis of synovial sarcoma. If the findings on preoperative MRI are doubtful, an open or needle biopsy should be performed.
Synovial sarcoma has three major histological subtypes: the biphasic, monophasic and poorly differentiated types [14
]. The co-existence of epithelioid cells and spindle cells is a hallmark of the biphasic subtype, while the monophasic subtype is entirely composed of spindle cells [15
]. The poorly differentiated subtype is a variant that lacks spindle cells and comprises primitive small round cells. Although there is a strong association between the poorly differentiated subtype and a poor prognosis, this variant of synovial sarcoma shares immunological, ultrastructural and molecular characteristics with the usual form of synovial sarcoma and is often diagnostically challenging [15
]. Poorly differentiated synovial sarcoma can be further divided into three types: a large cell epithelioid variant, a small cell variant and a high-grade spindle cell variant [15
]. In the present case, the presence of numerous small round cells with a high nucleocytoplasmic ratio was seen. This led to the initial diagnosis of a poorly differentiated synovial sarcoma, which was perhaps a small cell variant.
Immunohistochemically, most synovial sarcomas are positive for vimentin, cytokeratin and EMA, but have a lower immunoreactivity for S-100 and CD34 [8
]. Although they often co-express both cytokeratin and EMA, only one of them was positive in some cases [17
]. Positive staining for CD99 and bcl-2 is also present in many cases of synovial sarcoma [8
]. In addition, expression of calretinin, varying from focal to diffuse, is commonly seen in synovial sarcomas [18
]. Our case was strongly positive for vimentin and calretinin, moderately positive for CD99 and EMA, and only partially positive for cytokeratin. In addition, cytogenetics also plays an important role in the diagnosis of synovial sarcoma, especially the poorly differentiated subtype, since the reciprocal chromosomal translocation t(X;18) is highly specific for synovial sarcoma; however, this was not performed in our case.
Although curative resection and adjuvant irradiation can improve the local control of synovial sarcoma, metastases eventually develop in most patients. The lung and skeleton are the most commonly affected sites. Regional lymph nodes are involved in 10 to 23% of patients. In our case, although lung metastasis was not detected, pelvic and inguinal lymph node involvement was observed. The pitting edema could be caused by lymphedema due to the presence of lymph node metastases [19
]. Patients who develop metastatic soft tissue sarcoma are incurable in most cases, and judicious use of systemic treatment may provide symptom palliation, prevent rapid disease progression and prolong survival. Unfortunately, our patient deteriorated rapidly and died despite systemic therapy.