The performance of a modified RENAL nephrometry score in predicting renal mass radiofrequency ablation success.

OBJECTIVE

To assess the predictive performance of a modified RENAL nephrometry score for renal tumors undergoing radiofrequency ablation (RFA).

METHODS

Patients who underwent RFA were identified from 2002 to 2011, and RENAL nephrometry scoring was performed for each. A modified RENAL (m-RENAL) nephrometry score was created to account for the small sizes of tumors ablated for which the size variable, R, was adjusted. A size of 3 cm was calculated as the optimal cutoff for the R component of the m-RENAL nephrometry score, and tumors were given an R score of 1 if <3 cm, 2 if 3-4 cm, or 3 if >4 cm. Other RENAL variables were unchanged. Oncologic outcomes were stratified by complexity tertiles defined as low (4-6), medium (7-9), and high (10-12). Outcomes were reported as initial ablation success (IAS), recurrence-free survival (RFS), and metastatic-free survival (MFS). The Kaplan-Meir method was used to estimate survival based on complexity tertile.

RESULTS

Two hundred forty patients were identified who underwent RFA, of which 192 patients were eligible for analysis. Median follow-up was 32.2 months, and median tumor size was 2.4 cm. IAS was achieved in 185 of 192 patients (96.4%). Overall, the estimated 3-year RFS was 95.1% and MFS was 97.3%. There was no statistical difference between complexity tertiles using the standard RENAL nephrometry score; however, the m-RENAL nephrometry score was significantly associated with IAS and RFS (P = .027 and P = .003, respectively). There were too few events (n = 3) to perform statistical analysis for MFS.

CONCLUSION

A modification to the size variable increases the performance of the RENAL nephrometry score when used to stratify RFA ablation success.