Introduction

The histologic presence of residual RCC following thermal ablation without radiographic evidence of tumor is of uncertain clinical significance. The purpose of this study is to evaluate the incidence of viable RCC in patients with no radiographic recurrence following percutaneous microwave (MW) ablation.

Methods

Routine post-ablation biopsy was obtained approximately 9 months following ablation. Four cores were routinely sampled from the ablation bed (2 for H&E staining, 2 for NAD diaphorase testing). A pilot study included ex-vivo ablation of RCC immediately following nephrectomy to evaluate histologic effect of ablation.

Results

Pilot study included 10 patients who had nephrectomy for RCC. A sample containing tumor and normal renal parenchyma was evaluated histologically following ex-vivo supra-therapeutic MW ablation. Preservation of tumor histology was demonstrated in specimens evaluated after H&E processing. Fifty-six biopsy proven RCC tumors in 52 patients (37M/15F, median age: 67.5 IQR: 64 - 71.3) following percutaneous MW ablation from April 2012 through May 2016 were evaluated. Median tumor diameter and nephrometry score were 2.8 cm (IQR: 2.0 - 3.2) and 6.5 (IQR: 5.0 - 8.0). Median Charlson Co-Morbidity Index was 2.0 (IQR: 0.75 - 3.0). Clear cell histology represented 40/56 (71.4%). Median follow up was 15.3 months (IQR: 8.4 - 27.0). Median time between ablation and biopsy was 9.3 months (IQR: 9.0 - 10.3). Following ablation, ablation zone biopsy has no RCC present in 51/56 (91.1%) tumors while 5/56 (8.9%) had the appearance of histologically residual tumor. Positive versus negative post-ablation biopsies did not significantly differ in nephrometry score, age, tumor size, or histology (p > 0.05). In patients with residual tumor, 2 were treated with repeat ablation and 3 elected surveillance. No patients have subsequently developed radiologically identifiable kidney recurrence and one patient with negative renal ablation bed biopsy was treated surgically for recurrence outside kidney and is currently NED. _x000D_

Conclusions

Histologically identifiable tumor was identified in 9% of routine biopsies in the absence of radiologic recurrence following microwave ablation. The clinical significance of preserved tissue histology is unclear as no patients have radiological recurrence in ablated renal tumors to date.

Funding

None