Excise, Ablate or Observe: The Small Renal Mass Dilemma—A Meta-Analysis and Review

Purpose

The incidence of renal cell carcinoma is increasing due to the incidental detection of small renal masses. Resection, predominantly by nephron sparing surgery, remains the standard of care due to its durable oncological outcomes. Active surveillance and ablative technologies have emerged as alternatives to surgery in select patients. We performed a meta-analysis of published data evaluating nephron sparing surgery, cryoablation, radio frequency ablation and observation for small renal masses to define the current data.

Materials and Methods

A MEDLINE® search was performed for clinically localized sporadic renal masses. Patient age, tumor size, duration of followup, available pathological data and oncological outcomes were evaluated.

Results

A total of 99 studies representing 6,471 lesions were analyzed. Significant differences in mean patient age (p <0.001), tumor size (p <0.001) and followup duration (p <0.001) were detected among treatment modalities. The incidence of unknown/indeterminate pathological findings was significantly different among cryoablation, radio frequency ablation and observation (p = 0.003), and a significant difference in the rates of malignancy among lesions with known pathological results was detected (p = 0.001). Compared to nephron sparing surgery significantly increased local progression rates were calculated for cryoablation (RR = 7.45) and radio frequency ablation (RR = 18.23). However, no statistical differences were detected in the incidence of metastatic progression regardless of whether lesions were excised, ablated or observed.

Conclusions

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.

Key Words: kidney, kidney neoplasms, carcinoma, renal cell, natural history, nephrectomy

Abbreviations and Acronyms: CSS, cancer specific survival, CT, computerized tomography, MRI, magnetic resonance imaging, NSS, nephron sparing surgery, RCC, renal cell carcinoma, RFA, radio frequency ablation, SRM, small renal mass