Macroscopy: Labelled "Right pleural/lung biopsy". Multiple pale tan needle core biopsies 2-11 mm.
Microscopy: The biopsy cores show malignant tumour within sclerotic fibrous tissue. The tumour is composed of a haphazard arrangement of spindle cells with large, hyperchromatic pleomorphic nuclei and prominent nucleoli. Mitotic figures are fairly frequent, including atypical forms. There is partial tumour necrosis. No keratinisation or glandular formations are seen. No alveolated lung tissue is present.
Immunoperoxidase stains have been performed and the tumour cells show strong diffuse staining for CD99. There is no tumour cell staining for cytokeratin mix, CK 5/6, TTF-1, CD34, HBME1, calretinin, WT1 or p40. Additional immunostains are in progress.
Conclusion: Right pleural/lung, core biopsy: Sarcomatoid malignancy.
Additional immunostains have been performed and the tumour cells show strong positive staining for vimentin, with no staining for broad-spectrum cytokeratin (AE 1/3), EMA, BCL2, STAT6, S100 or desmin.
Based on this limited sample, the favoured diagnosis is of synovial sarcoma. Sarcomatoid carcinoma and mesothelioma have been considered, however, there is no tumour cell staining for cytokeratin or mesothelial markers to support these diagnoses.
This case was sent to another tertiary centre pathologist for review, who concurs with the diagnosis of sarcomatoid malignancy.