Kidney cancer. Principles and practice. Second edition. Primo N. Lara, Jr. Eric Jonasch (Editors). Springer International Publishing (2015)
Cryoablation versus radiofrequency ablation (RFA)
The diagnosis of localized RCC continues to increase with the widespread use of cross-sectional imaging for unrelated reasons , and localized RCC or small renal masses (SRMs) may account for as much as two-thirds of newly diagnosed RCC . Ablative techniques in the form of cryoablation or radiofrequency ablation (RFA) are attractive treatment modalities for elderly patients or patients with significant medical comorbidities because they are either percutaneous or minimally invasive, thus potentially avoiding the risks of both general anesthesia and major surgery. The recent AUA guidelines for the clinical T1 renal mass included the results of ablative techniques, which encompassed 34 studies with 1,389 patients undergoing either cryoablation or RFA. Recurrence-free survival rates for cryoablation and RFA were 90.6 and 87.0%, respectively . Major urological complications occurred in 4.9 and 6.0% of cryoablation and RFA cases .
Cryoablation results in tumor destruction by inducing rapid freeze-and-thaw cycles . Initial ice formation results in a number of physiological and mechanical cellular disruptions, including protein denaturation and cellular membrane disruption, ultimately leading to tumor kill . RFA relies on the conversion of radiofrequency waves to heat, resulting in thermal tissue damage . Similar to cryoablation, RFA results in tumor destruction by protein denaturation and cellular membrane disruption.
A recent meta-analysis comparing cryoablation to RFA of 47 series totaling 1,375 renal tumors found that intermediate oncologic efficacy may favor cryoablation . In this study, the authors found that patients undergoing RFA more often required a repeat ablative session (p < 0.0001) as well as having a higher rate of local tumor progression (p < 0.0001) . The higher incidence of local tumor progression occurring with RFA was confirmed on univariate (p = 0.001) and multivariate (p = 0.003) analysis . Finally, there was a higher incidence of progression to metastatic disease with RFA (2.5% vs. 1%); however, this did not achieve statistical significance (p = 0.06) .
These findings were consistent with another meta-analysis comparing excision, ablation, and observation of the small renal mass. In this study of 99 series including 6,471 renal tumors, the authors found a local recurrence rate of 4.6% after cryoablation and 11.7% after RFA . When compared to surgical excision, multivariate analysis revealed a significantly higher incidence of recurrence with cryoablation (RR = 7.45) and RFA (RR = 18.23) . No significant difference was seen between cryoablation and RFA for the development of metastatic disease.
Finally, a retrospective study from the Mayo Clinic compared PN, percutaneous RFA, and percutaneous cryoablation for cT1 renal masses. For patients with cT1a tumors, recurrence-free survival was similar among all three treatments . However, metastasis-free survival was significantly improved with PN (p = 0.005) and cryoablation compared to RFA (p = 0.021) . For patients with cT1b tumors, local recurrencefree survival (p = 0.81) and metastasis-free survival (p = 0.45) were similar between PN and cryoablation . Patients with cT1a and cT1b tumors who underwent PN had a significantly improved overall survival (p < 0.001) compared to patients who underwent ablation at 5 years of follow-up, potentially reflecting a patient selection bias due to medical comorbidities .
Percutaneous versus laparoscopic approach to ablation
Recently, ablative techniques for renal tumors have moved toward the use of cryoablation rather than RFA. Cryoablation can be performed both surgically—open or laparoscopically—and percutaneously. Theoretically, surgical cryoablation offers direct placement of cryotherapy probes and allows for real-time visual and continuous monitoring of ice ball formation and extension; however, surgical treatment subjects the patient to the risks of general anesthesia as well as the inherent risks of surgery. Percutaneous cryoablation has the potential advantages of improved patient tolerance, faster recovery, avoidance of general anesthesia, and lower periprocedural risks. Prior comparisons between the two approaches have focused on pain requirements and length of stay .
A recent meta-analysis of the literature was performed comparing the oncologic outcomes of surgical and percutaneous cryoablation of localized RCC. In this review, 42 studies including 1,447 renal lesions were pooled and analyzed. There was no significant difference in patient age, tumor size, or duration of follow-up between surgical and percutaneous cryoablation . The rates of residual tumor (p = 0.24) and recurrent tumor (p = 0.44) were not statistically significant between surgical and percutaneous cryoablation . In the reported literature, there were only two reports of the development of metastatic disease in the surgical group and one report in the percutaneous group . Based on these findings, the authors concluded that neither approach was superior.
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