A 37-Year-Old Man With a Pleural Mass

Abstract

A 37-year-old man presented to an outside hospital with a dry cough, progressive dyspnea, and left-sided chest pain of 1 month's duration. Chest radiography and computed tomography showed a large left pleural effusion and a left lung mass without hilar or mediastinal lymphadenopathy. Following thoracentesis of an apparent nonmalignant effusion, thoracoscopic pleural biopsy was performed. The patient was subsequently referred to our hospital, where he underwent thoracotomy with left upper lobectomy and partial pericardiectomy.Gross examination of the resected specimen revealed an 11.0 × 10.0 × 3.5-cm poorly circumscribed pleural tan-white mass with areas of hemorrhage, compressing the left upper lobe of lung and adherent to the pericardium. Multiple additional friable tissue fragments, 20.2 × 16.0 × 7.5 cm in aggregate, were present.Microscopically, the tumor was composed of sheets and long fascicles of densely packed, plump spindle cells with dark staining, oval nuclei, and scant cytoplasm (Figures 1 and 2). The degree of vascularity was variable, with focal hemangiopericytoma-like areas containing numerous dilated vascular spaces. Epithelioid cells, calcifications, or areas of ossification were not observed. Immunohistochemical studies for S100, CD34, keratin, and epithelial membrane antigen were negative. Bcl-2 immunohistochemistry was diffusely positive (Figure 3).Cytogenetic analysis demonstrated a t(X;18)(p11.2;q11.2) balanced reciprocal translocation (Figure 4). Following surgery, the patient was treated with ifosfamide chemotherapy and was alive and well, free of recurrent disease, 9 months after surgery.What is your diagnosis?Synovial sarcoma is a well-described soft tissue neoplasm, most often located in the extremities adjacent to large joints in adolescents and young adults 15 to 40 years of age. Despite its name, the tumor generally shows no association with joint cavities and has been described in numerous nonsynovial locations, including the heart, abdominal wall, parapharyngeal region, mediastinum, and pleural cavity. When these tumors arise from the pleura, patients often present with chest pain and dyspnea. Effusions and pleural-based masses may be noted radiographically. Computed tomographic scans typically demonstrate a soft tissue mass with intratumoral calcifications in 20% to 30% of cases.Gross pathologic examination reveals a localized mass, generally 5 to 20 cm in greatest dimension, consisting of gray-white to tan fleshy soft tissue.12 Hemorrhage, necrosis, cystic degeneration, and calcification are variably present. Similar to the para-articular synovial sarcomas, those in the pleural cavity are often completely or partially invested by a glistening pseudocapsule. In the thoracic cavity, distinction between pleural- and pulmonary-based lesions may be difficult, and tumors may be described as pleuropulmonary.3Microscopically, the tumors are classically composed of a biphasic pattern of epithelial and spindle cells. Monophasic patterns, as illustrated in this case, consist of either the spindle or the epithelial component; the former is more common than the latter. The epithelial cells are cuboidal to columnar, with vesicular nuclei and abundant pale-staining cytoplasm with distinct cellular borders, and are arranged in cords, nests, or glands. The surrounding densely packed sheets of spindle cells have plump, dark-staining nuclei with indistinct cytoplasm, often arranged in long, interweaving fascicles. Nuclear palisading in the spindle cell areas may be evident. Myxoid change, calcifications, and mast cells are variably present.Immunohistochemically, most synovial sarcomas display at least focal immunoreactivity for cytokeratin and epithelial membrane antigen, which is usually more prominent in the epithelial component. Multiple sections may need to be examined to identify positivity in the spindle cell areas, and even so, our case was negative for both stains. CD99 and Bcl-2 are also detected in the majority of cases. Synovial sarcomas are negative for CD34.The differential diagnosis of a spindle cell neoplasm in the pleural cavity includes sarcomatoid malignant mesothelioma,45 solitary fibrous tumor, hemangiopericytoma, and sarcomatoid carcinoma. Malignant mesotheliomas usually present in patients of older age (50–70 years) with antecedent asbestos exposure, and they diffusely involve the pleural cavity. Solitary fibrous tumor and hemangiopericytoma consistently express CD34, whereas synovial sarcoma does not. Other entities, such as fibrosarcoma, leiomyosarcoma, and malignant peripheral nerve sheath tumor, may share histologic similarities, but these are rare primary tumors of the pleural cavity, distinguishable by immunohistochemistry. In addition, because synovial sarcoma preferentially metastasizes to the lung, an extrathoracic primary origin should be ruled out.The chromosomal translocation t(X;18)(p11.2;q11.2), which has been identified in more than 90% of synovial sarcomas, results in an SYT-SSX gene fusion.67 Detection of this translocation by conventional cytogenetics, fluorescence in situ hybridization, or reverse transcriptase polymerase chain reaction8 is helpful in establishing the diagnosis, particularly in monophasic variants.9Treatment for synovial sarcoma has included surgical resection, chemotherapy, and radiation. Favorable prognostic factors include a tumor size less than 5 cm, low mitotic rate (<10 mitotic figures per 10 high-power fields), absence of necrosis, and local eradication. Metastases occur in approximately half of the cases, and these may be noted many years following the initial diagnosis. Five-and 10-year survival rates range from 36% to 76% and 20% to 63%, respectively.10