Introduction:

The proportion of incidentally detected small renal masses (SRM) has increased due to the widespread use of cross-sectional imaging. The management of clinically localized SRM includes active surveillance, thermal ablation and surgery. As the understanding of the importance of renal function preservation emerged, the utilization of nephron-sparing approached increased. Several ablative energies have been applied for SRM including cryoablation (CA),  radiofrequency ablation (RFA) and microwave ablation (MWA). The ideal circumstance for ablation is a small, clinically localized mass. No RCT comparing surgery and ablation exists, yet retrospective studies have observed durable local control with RFA and CA for T1a renal cell carcinoma (RCC). Although recurrence and retreatment rates are higher for ablation, the overall survival and cancer-specific survival rates are comparable between thermal ablation and partial nephrectomy. We present our experience in managing cT1a renal masses treated with partial nephrectomy (PN) and ablation (RFA, CA, and  MWA).

Methods:

All patients treated at our institution with PN or percutaneous ablation (PA) for sporadic, localized cT1aN0M0 masses between 2010 and 2017 were identified. PN was carried out by either an open or robotic-assisted approach. PA procedures included RFA, CA and MWA. Exclusion criteria included: multiple lesions, prior RCC, known genetic syndrome, ablation done in the setting of metastatic RCC and missing data. Clinical and pathologic features were collected, complications within 30 days of the procedure were recorded. Outcomes included changes in renal function, repeat ablation procedures, salvage nephrectomy, local recurrence, development of metastatic disease and death. Comparisons of features by treatment were compared using independent t-test and chi-square. Overall survival and recurrence-free survival were estimated using the Kaplan-Meier method and compared among treatments using log-rank tests. Because of the few cancer-related deaths, cancer-specific survival was not analyzed. All tests were two-sided, with p-values <0.05 considered significant.

Results:

The cohort consisted of 269 patients with cT1aN0M0 renal masses. PN occurred in 112 patients, RFA in 104, CA in 46, and seven patients underwent MWA. Patients treated with PN were younger, had a lower CCI and a higher eGFR. Tumor size was comparable between groups. In the ablative group, 21% of patients had no definitive tissue diagnosis before treatment. Any complication was recorded in 7% and 31.25% for PA vs. PN, respectively (p<0.001). Mean postoperative decrease in eGFR was significantly lower (8.7 and 18.7, p<0.001), in the PA group vs. PN group, respectively. The rate of postprocedure renal dialysis was 5.1% vs. 0.9% in the PA vs. PN, respectively (p=0.059). At a median follow-up of 27.74 months and 29.86 months, the recurrence rate (beyond 3 months) was 8.9% and 2.7% for PA vs. PN, respectively (p=0.038). No significant difference in overall survival was found between the groups (p=0.16).

Conclusion:

With an intermediate follow-up at a single institution, PA has an acceptable functional outcome with fewer perioperative complications for cT1a renal masses. Recurrence rates, as well as retreatment rates, were higher in the PA compared to PN. Nevertheless, overall survival rates were similar among management strategies. Another significant advantage is the relative ease of performing repeated treatment if persistent or recurrent lesion is detected. In conclusion, PA is an appropriate treatment option for patients that are not surgical candidates or opt for ablation treatment. Differences in renal functional outcomes, perioperative outcomes, retreatment rates, and oncological outcomes should be discussed in shared decision-making when counselling patients with small renal masses. 

Funding: N/A