Pulmonary synovial sarcoma
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CXR demonstrates a very well circumscribed mass in the left upper zone. The differential is that of a solitary pulmonary mass.
A lobectomy specimen, consistent with left upper lobe, 140 x 130 x 30mm, with attached bronchial remnant, 15mm in diameter and 6mm long. In the middle of the left upper lobe towards to the anterior surface, is a relatively well circumscribed, irregular, soft shiny and tan tumour, 60 x 35 x 45mm. It is 4mm from the pleural surface. The overlying pleura is smooth and glistening. The tumours appears to be within 1mm of the bronchus, but does not appear to invade through it. It is approximately 5mm from the bronchial resection margin. Elsewhere, the lung parenchyma is variegated brown tan, with patchy, pale regions, more prominent towards the superior aspect and anterior inferior aspect.
Sections from the macroscopically described lesion show a well circumscribed, highly cellular neoplasm composed of interlacing fascicles of plump spindled cells separated by small or ectatic thin-walled blood vessels. The tumour cells possess overlapping, large, elongate ovoid nuclei with multiple small nucleoli, and frequent mitotic figures are noted (21/10hpf). There are large areas of necrosis. There are also less cellular, oedematous foci scattered throughout. In areas, tumour bulges into an bronchioles, undermining epithelium, but there is no cystic component. No lymphovascular space invasion is seen, and the lesion is clear of the pleural surface. No rhabdomyosarcomatous or chondroid differentiation is seen. Immunohistochemical stains have been performed, and the tumour cells show diffuse immunoreactivity for vimentin, CD99, bcl-2 and CD56. There is focal immunoreactivity for calretinin and weak and patchy immunoreactivity for epithelial membrane antigen. The tumour cells are negative for cytokeratins (AE1/AE3, cytokeratin 7, cytokeratin 5/6), S100 protein, gp-100, desmin, smooth muscle actin, CD34, synaptophysin and TTF-1. Overall, the features are most in keeping with a monophasic pulmonary synovial sarcoma.
FISH studies were POSITIVE for SYT (18q11.2) breakapart rearrangement in >50% of cells examined which is consistent with a diagnosis of synovial sarcoma. The accuracy of these results is dependent on the correct identification of tumour on the sections provided, and the assumption that positive results will be identified by a large proportion of cells within the tumour having a rearrangement.
Malignant spindle cell tumour with features favouring monophasic pulmonary synovial sarcoma, 60 mm diameter, clear of margins, with no lymph node metastases identified.