Primary Pulmonary Poorly Differentiated Synovial Sarcoma: Transducer-Like Enhancer of Split 1 Immunohistochemistry as A Valuable Diagnostic Aid
A 26-year old male presented with an increasing breathlessness over the previous 15 days accompanied by an episode of hemoptysis. On examination, he was moderately built, had low grade fever and absent breath sounds in the right lower chest. On investigation, hemoglobin and the blood counts were in normal range. Chest radiograph revealed features suggestive of a mass lesion with well-defined margins within the right lower lobe. This was followed by a high resolution computerized tomogram, which further confirmed the presence of the mass and showed it to be pulmonary and not pleural in nature. A lobectomy resection was carried out as he was determined to have no other primary site of tumor.\nGross examination revealed a heavy boggy right lower lobe with a congested pleural surface. On sectioning, a well-defined fleshy mass (13 × 12 × 5 cm) with areas of necrosis and hemorrhage involving almost the entire lower lobe was present. The mass seemed to involve the medial aspect of the lobe including the hilar area with some residual remnant of parent lung in the periphery [].\nMicroscopy revealed a cellular unencapsulated neoplasm with tumor cells in vague lobulated sheets with pushing margins []. The compact spindle cells most characteristic of synovial sarcoma were largely absent. In most areas, the cells appeared small and round with round to ovoid nuclei and a small amount of eosinophilic cytoplasm []. In only a few areas was their some degree of spindling with cells growing in fascicular arrays []. In places, the cells were in nests separated by fine branching staghorn or hemangiopericytomatous type blood vessels []. Mitosis was brisk (10-14 mitosis/10 HPF). Large areas of geographic necrosis were also present. The differential diagnosis considered based on an initial histology included a neuroendocrine tumor, Ewing's sarcoma, peripheral neuroectodermal tumor (PNET), solitary fibrous tumor, and poorly differentiated synovial sarcoma.\nImmunoperoxidase studies on paraffin embedded tissue revealed the neoplastic cells to be focally reactive with antibodies to pancytokeratin along with reactivity for epithelial membrane antibody in approximately 25% of the cells. They failed to react with antibodies to thyroid transcription factor 1 (TTF-1), synaptophysin, smooth muscle actin, S100 protein, CAM5.2, CD99, chromogranin, CD45 and CD34. With the above IHC findings, a poorly differentiated synovial sarcoma was considered most likely and a TLE-1 stain was carried out, which revealed diffuse nuclear reactivity of the tumor cells []. This stain provided the definitive diagnosis of a synovial sarcoma. The patient was subjected to chemotherapy; however, over the next 4 months, he developed extensive metastatic disease and eventually succumbed to his illness.