A Case of Alveolar Soft Part Sarcoma of the Pleura
A 58-yr-old man presented with progressive dyspnea on July 1, 2009. He also complained of cough and whitish sputum. He was an ex-smoker. Twenty years previously, a right nephrectomy had been performed at another hospital because of a right renal mass. The final pathologic findings were consistent with typical low-grade clear cell renal cell carcinoma (T1N0M0). A chest radiograph obtained upon admission showed a large pleural effusion in the left lung (). Computed tomography (CT) images of the thorax showed a large enhancing pleural mass with pleural effusion in the left hemithorax, a 1.6 × 1.3 cm pulmonary nodule in the left upper lobe (LUL), and a right lower pleural nodule (). Positron emission tomography-computed tomography (PET-CT) images showed a large left pleural effusion with heterogeneous hypermetabolic activity, mild-to-moderate hypermetabolic activity in the left lower paratracheal area, and a focal hypermetabolic nodular lesion in the LUL. No extrapulmonary lesions were seen on the PET-CT images ().\nAlthough both cytologic and pathologic study of the pleural effusion and tissues obtained by diagnostic thoracentesis and pleural biopsy revealed atypical hyperchromatic and cytopathic cells, these findings were not sufficient for a definitive diagnosis. Thus, we performed excisional biopsy of the pleural mass by video-assisted thoracoscopic surgery (VATS). Because the biopsy result was suspicious for ASPS, we decided on open thoracotomy for a wide excision of the pleural mass with wedge resection of the pulmonary nodule in the LUL. Gross examination of the left pleural mass revealed a firm, 18.0 × 16.0 × 5.0 cm bilobulated, gray-white tumor with focal areas of necrosis and hemorrhage. Gross examination of the lung nodule showed a fragment of soft tissue that measured 1.5 × 1.2 cm. Pathologic examination of both pleural and lung specimens revealed an organoid or nested arrangement of tumor cells resulting in a pseudoalveolar pattern. The tumor cells were separated by fibrovascular septa and delicate capillary-sized vascular channels. The individual cells were large, rounded, or polygonal with one or two large nuclei and prominent nucleoli. The cytoplasm was abundant and appeared granular and sometimes vacuolated (). Under Periodic acid Schiff staining with diastase treatment (D-PAS), abundant PAS-positive granules appeared in the tumor cells (). The immunohistochemistry results were positive for TFE3 () and vimentin; equivocal for CD56, chromogranin, synaptophysin, and WT-1; and negative for epithelial membrane antigen (EMA), cytokeratin (CK), CK5/6, CK7, CK20, CD10, CD30, CD34, CD68, calretinin, CEA, smooth muscle actin (SMA), desmin, HMB-45, and S-100 protein.\nBecause it was necessary to rule out the metastasis of renal cell carcinoma to the pleura, which can generate similar pathologic findings to those of ASPS, we borrowed a slide from another hospital to review the pathologic findings of a renal tumor that was resected 20 yr previously and diagnosed as a low-grade clear cell renal cell carcinoma, and to compare the pathologic findings with those of a pleural tumor diagnosed as ASPS. The renal tumor cells had clear cytoplasms, distinct cell borders, small nuclei, and at low magnification, barely visible nucleoli. They were arranged in small solid nests (). These pathologic findings are typical of a low-grade clear cell renal cell carcinoma and are clearly different from our pathologic finding of ASPS.\nElectron microscopy showed that the cells contained numerous mitochondria, prominent rough endoplasmic reticulum, well-developed Golgi complexes, and many membrane-bound electron-dense granules ().\nWe recommended adjuvant chemotherapy after wide resection of the pleural tumor and metastasectomy of the lung nodule. However, the patient refused further treatment. The pleural ASPS with multiple bone metastases recurred 1 yr after surgery. The patient died of acute pulmonary embolism 1.5 yr after diagnosis.