Microwave ablation of the T1a small renal mass: expanding beyond 3 cm.

Purpose: To compare the oncological and renal function outcomes for patients receiving microwave ablation (MWA) in tumors < 3 and 3-4 cm.

Methods: Retrospective analysis of a prospectively maintained database identified patients with < 3 or 3-4 cm renal cancers undergoing MWA. Radiographic follow-up occurred at approximately 6 months post-procedure and annually thereafter. Serum creatinine and estimated glomerular filtration rate (eGFR) were calculated before and 6-months post-MWA. Local recurrence-free survival (LRFS) was estimated using the Kaplan-Meier method. Tumor size was evaluated as a prognostic factor using Cox proportional-hazards regression. Predictors for change in eGFR and chronic kidney disease (CKD) stage were modeled using linear and ordinal logistic regression.

Results: A total of 126 patients fit the inclusion criteria. Overall recurrences were 2/62 (3.2%) and 6/64 (9.4%) for < 3 versus 3-4 cm. Both recurrences in the < 3 cm group were local, 4/6 in the 3-4 cm group were local and 2/6 were metastatic without local progression. For < 3 versus 3-4 cm, cumulative LRFS at 36 months was 94.6% versus 91.4%. Tumor size was not a significant prognostic factor for LRFS. Renal function did not change significantly after MWA. Patient comorbidities and RENAL nephrometry score significantly affected change in CKD.

Conclusion: With comparable oncological outcomes, complication rates, and renal function preservation, MWA is a promising management strategy for renal masses of 3-4 cm in select patients. Our findings suggest that current AUA guidelines, which recommend thermal ablation for tumors < 3 cm, may need review to include T1a tumors for MWA, regardless of size.