Sarcomatoid renal cell carcinoma (sRCC) may develop when one of the more common subtypes of renal cell carcinoma degenerates into a sarcoma. It is generally irregular and malignant-appearing on imaging, but does not have specific imaging features.
The sarcomatoid variant has been estimated to occur in ~16% of cases of advanced renal cell cancer. Approximately 5% of renal tumours my contain elements of sarcomatoid transformation.
Highly aggressive variant associated with metastatic disease. ~90% are symptomatic at presentation 4.
Once a separate category, it is now known that sRCC can develop from all other histologic subtypes. It demonstrates spindle cells, high cellularity, and cellular atypia. It is associated with extensive chromosomal rearrangements 2.
It has been described as "the final common dedifferentiation pathway" of renal tumors 3.
Ultrasound or CT-guided fine needle aspiration (FNA) can be problematic since half of these tumors contain <50% sarcomatoid elements.
A diagnosis of sRCC is based on histology and it currently has no specific imaging features. Its appearance is similar to advanced renal cell carcinoma, although sRCC has a tendency to be necrotic.
- tend to be large at diagnosis (~9-10 cm)
- tends to present with metastatic disease (>45%)
MRI may show a heterogeneous renal mass with areas of low T2 signal intensity, but this appearance lacks specificity 6.
Treatment and prognosis
Currently, the biology of sRCC is poorly understood. Since it generally develops from advanced renal cell cancer, and often presents with metastases, it is difficult to treat effectively. Prognosis is worse than equivalent size and stage nonsarcomatous RCC.
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