Schmidt et al. present a retrospective review of percutaneous renal mass cryoablation in 116 patients with biopsy-proven RCC. The median tumour size was 3.4 cm and 95% of the lesions were T1a or T1b, with a median RENAL score of 7. There was only one technical failure. Among the 88 patients with at least 3 months of follow-up, there was one recurrence with median follow-up of 22 months. As expected, Clavien ≥3 complications increased with clinical tumour stage: 4% in T1a, 15% in T1b, and 33% in T2.
Several points about this study merit further discussion. First, 79 patients who underwent cryoablation without a diagnosis of RCC were excluded from the study. These patients could have been included in the assessment of local recurrence/progression (considering that both benign and malignant lesions have the potential to grow), perioperative outcomes such as technical success and complications, as well as overall survival.
Second, with follow-up of only 22 months, it is not clear that the intervention in this series altered the natural history of what is possibly an indolent disease in some patients. Few of the patients in this series had high-risk features on biopsy, with Grade 3 and 4 disease in 13% and 3%, respectively. Additionally, 20% of the patients had papillary or chromophobe tumours, which typically behave less aggressively than clear-cell tumours when clinically localized.
Third, it is important to note that the authors chose to define recurrence based solely on radiographic findings. Contrast-enhanced imaging does not have perfect sensitivity to detect recurrence. In one study, 46% of patients with a positive biopsy after renal mass ablation did not have an enhancing recurrence on imaging .
Fourth, only 88 patients had imaging available at 3 months, leaving 24% of the study patients (28 of 116) without any radiographic follow-up. This lack of adequate follow-up (regardless of the reasons) is quite concerning, given the lack of long-term data regarding efficacy of percutaneous cryoablation.
Finally, the authors describe their work as ‘an initial effort to compare and contrast efficacy and complications of renal cryoablation vs. surgery’ and then compare their results with those of published partial nephrectomy series. Indeed, a study comparing robotic partial nephrectomy and laparoscopic cryoablation at a single institution was recently published . However, no real comparisons can be made as the two groups had very different baseline characteristics (such as younger and healthier patients treated with surgery) and very different follow-up durations. In the present study, Schmidt et al. report that 71% of the patients were not surgical candidates owing to ‘significant medical comorbidities’. The relative poor health of the population (with a median age of 72 years, up to 92 years of age) is affirmed by the 14% rate of non-RCC deaths during the short follow-up period. It is possible that some of these patients might have benefited from active surveillance.
Realistically, as long as cryoablation is being offered mostly to poor surgical candidates, we should forgo the idea of comparing cryoablation to nephrectomy (partial or radical); such comparison is clinically irrelevant owing to the aforementioned differences (mainly that these procedures are offered to different patient populations). A more relevant study would compare active surveillance with cryoablation (or radiofrequency ablation) in a cohort of patients with reasonably small renal masses who are otherwise poor surgical candidates . Such a study could bring to light the proper role of energy ablation in the RCC treatment algorithm.