Synovial sarcomas are very rare tumours, and primary location is an exceptional finding. We present the case of a 46-year-old patient with a late diagnosis of a primary thoracic monophasic synovial sarcoma.

A 46-year-old man was admitted to hospital due to progressive dyspnoea and a painless axillary mass that he had had for several months (Fig. 1). Histology revealed a spindle cell tumour with mixed cellularity, focal myxoid changes, sparse collagen and mitotic figures. Epithelial membrane antigen was also found. The differential diagnosis included spindle cell tumour variants: liposarcomas, leiomyosarcoma, malignant peripheral nerve sheath tumour, malignant fibrous histiocytoma and monophasic synovial sarcoma (MSS). MSS was confirmed by S-100 negativity and muscle markers. The patient underwent tumour resection, chemotherapy with ifosfamide and radiotherapy, but the tumour returned and he died as a result of pericardial effusion.

Fig. 1.

Intra and extra-thoracic MSS localization.

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Pulmonary sarcomas are a very rare histological variety, and the MSS group is particularly rare. The majority are metastases from a primary tumour at any site.1 Primary pulmonary sarcomas represent about 0.5% of lung cancers.2 Diagnosis can only be established after all other possible sites explaining that the pulmonary extension has been ruled out by clinical examination and imaging techniques. A detailed immunohistochemistry study is also required to exclude other spindle cell tumours. Leiomyomas, fibrosarcomas and hemangiopericytomas are the most common varieties of primary sarcoma of the lung.3

Synovial sarcoma is a tumour that is well defined morphologically, and occurs most frequently in the soft tissue. This type of tumour represents 10% of all tissue sarcomas. It is classified into four histological subtypes: biphasic, monophasic fibrous, monophasic epithelial and poorly differentiated. However, the monophasic epithelial subtype (presented here) is extremely rare.4

Thoracic MSS typically occurs in the form of a mass in the ribcage, although they may also emerge from the lung and the pleura. Generally they occur in adults, and the mean age at diagnosis is 38 years.5 Patients with chest wall involvement have chest pain that is difficult to manage even with potent analgesics, dyspnoea and cough.

Treatment of thoracic MSS requires an integral approach, including surgery, radiotherapy and chemotherapy protocols (principally with ifosfamide). Median 5-year survival is 50%.