Tissue shows in areas unremarkable surface epithelium comprising urothelium. Most of the tissue shows a malignant spindle cell tumour comprising fascicles of moderately pleomorphic spindle cells with ovoid nuclei. There are frequent apoptotic bodies and mitosis are plentiful (approximately 12 per 10 high power field). There are areas of necrosis. Some of the tumour shows focal myxoid areas. There is no definite skeletal or smooth muscle differentiation, nor is there a heterologous component. There is no malignant epithelial component. The tumour infiltrates into bundles of smooth muscle presumably muscularis propria (detrusor). There are also foci of lymphovascular space invasion.
The neoplastic cells show diffuse strong staining with vimentin. They are negative for a panel of cytokeratin stains (AE1/3, PAN and EMA), PSA (prostate specific antigen), muscle markers dermisn, smooth muscle actin (SMA) and caldesmon and melanoma markers gp-100 and Mel-A. There is focal, weak equivocal staining of some cells with S-100, and the significance of this is uncertain.
The morphology is of a malignant sarcomatoid neoplasm, and in view of the negative keratin staining, it is most likely a sarcoma.
The differential diagnosis (which hasn't been entirely excluded) includes a monomorphic synovial sarcoma for which cytogenetic studies to demonstrate the diagnostic translocation t(X;18) will be necessary. A spindle cell rhabdomyosarcoma has been considered in the differential diagnosis but this is considered less likely as most of these tumours are desmin-positive and there are morphologically identifieable rhabdomyoblasts (which are not seen in this case).
Transurethral biopsies - high grade sarcoma with lymphvascular invasion, morphology initially suggesting a synovial sarcoma. FISH studies are NEGATIVE for SYT (18q11.2) breakapart signals however.
(X;18) translocation associated with synovial sarcoma NOT detected.
In view of the negative FISH study, this tumour is best considered a high grade sarcoma, NOS.