Nicotinamide adenine dinucleotide staining immediately following radio frequency ablation of renal tumors-is a positive stain synonymous with ablative failure?

PURPOSE: Nicotinamide adenine dinucleotide diaphorase staining is arguably the standard for assessing tissue viability following radio frequency ablation, yet the accuracy of this test is questionable. Thus, it is imperative to examine the reliability of nicotinamide adenine dinucleotide to predict ablation success. To evaluate the observation that immediate nicotinamide adenine dinucleotide staining may not be clinically reliable, we compared results from immediate post-ablation biopsies of renal tumors to radiological and clinical followup.
MATERIALS AND METHODS: Laparoscopic radio frequency ablation was performed in 9 patients and 10 tumors using a temperature modulated radio frequency system. Cold cup biopsies were taken immediately following ablation, and processed for nicotinamide adenine dinucleotide and hematoxylin and eosin staining. Patients were then followed using contrast enhanced computerized tomography at regular intervals.
RESULTS: Median tumor size was 2.3 cm. Hematoxylin and eosin stain diagnosed 8 renal cell carcinomas and 2 angiomyolipomas. A quarter of the renal cell carcinomas and both angiomyolipomas stained positive for scattered nicotinamide adenine dinucleotide diaphorase activity immediately after RFA. Mean followup for the nicotinamide adenine dinucleotide positive tumors was 28.5 months (range 24 to 30) and for the nicotinamide adenine dinucleotide negative tumors was 25 months (range 18 to 30). There was no evidence of local tumor recurrence in any patient.
CONCLUSIONS: Four lesions had nicotinamide adenine dinucleotide diaphorase activity on post-ablation biopsy suggesting retained viable tissue, yet there has been no recurrence during an average 2-year followup. While negative nicotinamide adenine dinucleotide staining is consistent with nonviability, these results suggest that false-positive staining can occur immediately following RFA, making the predictive value of positive nicotinamide adenine dinucleotide diaphorase staining unclear.