Sarcomas are very rare in the urinary tract proper (« 1 %). Rhabdomyosarcoma is the most common in children and young adults; leiomyosarcoma is more prevalent in the older age groups. Malignant fibrous histiocytoma is reported as the second most common sarcoma may be over-reported.
Embryonal rhabdomyosarcoma is the most common subtype in children.
There are two common appearances:
- Polypoid and minimally invasive (good prognosis)
- Extensively infiltrative, invasive into neighbouring organs (poor prognosis)
The embryonal rhabodmyosarcoma cells are usually small and round. They lie within a myxoid stroma. The cells are usually positive on immunohistochemistry for myogenin.
The most common sarcoma of the adult bladder. It commonly presents with haematuria.
The mean size of these tumours is 7 cm at diagnosis. Necrosis may be apparent. The tumour is typically infiltrative.
Spindle cells arranged in fascicles are the classical appearance. Nuclear pleomorphism and cellular atypia allow grading into poorly and well differentiated tumours. On immunohistocheistry, the cells are negative for cytokeratins (important to exclude sarcomatoid differentiation of a urothelial malignancy). Positive staining for smooth muscle actin (SMA) and desmin is common.
Other types of sarcoma are extremely rare:
- Angiosarcoma has been reported ten times, once in a patient 20 years after radiotherapy
- Osteosarcoma has been reported several times
- Malignant fibrous histiocytoma is more commonly reported, but there is debate about its true prevalence as it can be confused with urothelial malignancy with sarcomatoid differentiation