Nephron sparing surgery, ablation and surveillance are viable strategies for small renal masses based on short-term and intermediate term oncological outcomes. However, a significant selection bias exists in the application of these techniques. While long-term data have demonstrated durable outcomes for nephron sparing surgery, extended oncological efficacy is lacking for ablation and surveillance strategies. The extent to which treatment alters the natural history of small renal masses is not yet established.

BACKGROUND.The incidence of renal cell carcinoma is rising because of incidental detection of small renal masses (SRMs). Although surgical resection remains the standard of care, cryoablation and radiofrequency ablation (RFA) have emerged as minimally invasive treatment alternatives. The authors of this report performed a comparative meta‐analysis evaluating cryoablation and RFA as primary treatment for SRMs.METHODS.A search of the MEDLINE database was performed reviewing the world literature for clinically localized renal masses treated by cryoablation or RFA.RESULTS.Forty‐seven studies representing 1375 kidney lesions treated by cryoablation or RFA were analyzed. No differences were detected between ablation modalities with regard to mean patient age (P = .17), tumor size (P = .12), or duration of follow‐up (P = .53). Pretreatment biopsy was performed more often for cryoablated lesions (82.3%) than for RFA (62.2%; P < .0001). Unknown pathology occurred at a significantly higher rate for SRMs that underwent RFA (40.4%) versus cryoablation (24.5%; P < .0001). Repeat ablation was performed more often after RFA (8.5% vs 1.3%; P < .0001), and the rates of local tumor progression were significantly higher for RFA (12.9% vs 5.2%; P < .0001) compared with cryoablation. The higher incidence of local tumor progression was found to be correlated significantly with treatment by RFA on univariate analysis (P = .001) and on multivariate regression analysis (P = .003). Metastasis was reported less frequently for cryoablation (1.0%) versus RFA (2.5%; P = .06). Cryoablation usually was performed laparoscopically (65%), whereas 94% of lesions that were treated with RFA were approached percutaneously.CONCLUSIONS.Ablation of SRMs is a viable strategy based on short‐term oncologic outcomes. Although extended oncologic efficacy remains to be established for ablation modalities, the current data suggest that cryoablation results in fewer retreatments and improved local tumor control, and it may be associated with a lower risk of metastatic progression compared with RFA. Cancer 2008. © 2008 American Cancer Society.

We were unable to identify definable clinical characteristics to predict the future growth of enhancing renal masses under active surveillance. Our analysis demonstrated that 26% to 33% of these tumors do not demonstrate growth at 29 months median followup. These lesions have similar rates of malignancy compared to growing lesions and rates of progression to metastatic disease are similarly low. A brief period of active surveillance may be feasible with treatment limited to lesions that increase in size.