New ablative treatments for small renal masses: HIFU ablation

Solid renal tumours with a diameter <4cm comprise up to half of all renal tumours coming for a therapeutic decision in tertiary care centres today. ∼80% are renal cell cancers, and nephron-sparing excision is standard therapy. The approach has considerable morbidity , and as many of these tumours are diagnosed in elderly ,infirm patients less invasive focal ablation appears attractive. This is usually achieved with radiofrequency or cryoablation, either percutaneously under image guidance or by a laparoscopic approach. The quality of reports on the outcome with this treatment is moderate, with no prospective comparative studies, and in general short follow-up. Metanalyses suggest more reliable results with cyro- than with radiofrequency ablation . Morbidity is lower than with nephron-sparing surgery, but still substantial and almost entirely due to the perforating trauma at ablation. This would be avoided by energy ablation with high-intensity focused ultrasound from an extracorporeal energy source. Phase 1 clinical studies with several prototoypes have been disappointing, as multiple acoustic interphases and target mobility obviously render adequately precise focusing unreliable. New HIFU transducers that can be approximated directly to the tumour via a laparoscopic approach circumvent these problems. A phase 1 study with this technique in 31 patients demonstrates that complete ablation of tumours can be achieved in this manner, at least for tumours <3cm and in a peripheral position in the lower and middle third of the kidney. Perforating trauma to the kidney is avoided, and morbidity is minimized. Of course patients still need long - term follow-up with sequential imaging and even biopsies, and tumour control is most likely less reliable than with standard nephron-sparing surgery.