Correspondence Fox Chase Cancer Center, Temple University School of Medicine, 333 Cottman Avenue, Philadelphia, PA 19111, USA

Email robert.uzzo@fccc.edu

Original article

Zagoria RJ et al. (2007) Oncologic efficacy of CT-guided percutaneous radiofrequency ablation of renal cell carcinomas. AJR Am J Roentgenol 189: 429–436   PubMed

Synopsis

Background

CT-guided percutaneous radiofrequency ablation has been shown to be effective in patients with small renal cell carcinoma (RCC); however, data concerning the oncological efficacy are limited.

Objective

The objective was to assess the safety and efficacy of CT-guided percutaneous radiofrequency ablation in patients with RCC.

Design and intervention

This retrospective, single-center study evaluated patients with biopsy-proven RCC who had an increased risk of surgery-related complications, and who underwent percutaneous radiofrequency ablation between May 2000 and June 2006. Pretreatment assessment included abdominal CT or MRI (before and after contrast enhancement), chest CT or radiography, and laboratory investigations. A urologic surgeon determined whether patients were suitable for ablation. Radiofrequency ablation was performed by a single radiologist using a 200 W generator and saline-cooled treatment probes (Cool-Tip^™, ValleyLab, Boulder, CO). Renal CT was performed immediately after treatment to assess tumor destruction; if the tumor was incompletely ablated, additional tumor ablation was performed. Radiographic follow-up was performed 1–3 months after surgery and at regular intervals thereafter. Post-treatment biopsies were not routinely obtained. Patients with radiographic recurrent or persistent disease were assessed as candidates for further ablation therapy. Patients were excluded from the analysis if they had pretreatment evidence of metastatic disease or local spread to the renal vein, if they had not been followed-up, or if they had stage III or IV disease treated for symptomatic relief or cytoreduction only.

Outcome measures

The outcome measures for this study were tumor-free survival (measured by post-radiofrequency ablation enhancement) and treatment complications.

Results

This study included 104 patients with a total of 125 RCCs. The mean patient age was 70.4 years and 66% of patients were men. The median duration of follow-up was 9.8 months. The mean tumor size was 2.7 cm. The tumor types were judged as exophytic, parenchymal, central or mixed in 75%, 16%, 1% and 8% of cases, respectively, and were located in the inferior pole, interpolar region, or the superior pole in 31%, 38%, and 32% of cases, respectively. Tumor-free survival (lack of enhancement) was achieved with 93% of tumors. Patients with tumors in the lateral position had slightly better outcomes than patients with tumors in the medial half of the kidney (P = 0.05). Tumor-free survival was not influenced by sex, side of tumor, tumor type, or tumor location within the kidney, but was associated with tumor size (P <0.0001); 100% of patients with tumors 3.6 cm achieved tumor-free survival, compared with 47% of patients with tumors >3.7 cm. Initial treatment failure occurred in 15% of patients, and 44% of these patients were successfully re-treated. Treatment complications were experienced by 8% of patients, and were not associated with sex, side of tumor, tumor type, tumor location within the kidney, or tumor size.

Conclusions

CT-guided percutaneous radiofrequency ablation is safe in patients with small RCCs.

Commentary

The standard of care for treating clinically localized RCC is surgery. Patients who undergo open or laparoscopic radical or partial nephrectomy for pT1a (<4 cm) tumors have demonstrated 5-year cancer-specific survival rates as high as 97%.¹ Ablative technologies have now emerged as potential treatment options for clinically localized RCC. Technically effective renal cryoablation and radiofrequency ablation have been achieved by open, laparoscopic and percutaneous techniques. While these methods seem promising, consistent long-term data demonstrating efficacy are lacking. Moreover, data from patients with localized small renal masses (SRMs) managed by active surveillance show that SRMs have slow growth kinetics and a low risk of progression,² which makes observation with delayed intervention a consideration in selected patients.³

These data underscore the clinical dilemma of managing SRM, namely that excision, ablation and observation all seem to be effective strategies that are associated with a low risk of death from RCC in appropriate patients; however, noteworthy differences in the literature regarding these techniques exist. A recent meta-analysis that evaluated the current literature included 99 studies and 6,471 lesions that had been excised (n = 5,037), cryoablated (n = 496), radiofrequency ablated (n = 607) or observed (n = 331).² Younger patients with larger tumors tended to undergo excision (P <0.5). The mean tumor size was largest in patients treated with surgery, smallest in patients treated with ablation, and in between these two in patients under surveillance (P <0.05). The cumulative mean length of follow-up reported was 45, 32, 15 and 15 months for patients who underwent excision, observation, cryoablation and radiofrequency ablation, respectively. While RCC was confirmed by pathology in 85% of excised SRMs, such confirmation was only available in 60%, 50% and 43% of patients who underwent cryoablation, radiofrequency ablation and observation, respectively. A multivariate regression analysis of data from the literature noted an 18-fold higher risk of local recurrence following radiofrequency ablation and a 7-fold higher risk after cryoablation compared with excision, while the cumulative risk of metastatic progression was twofold higher following radiofrequency ablation than excision or observation.⁴

These and other data highlight fundamental concerns regarding the treatment of SRMs, namely that the data used to assess the therapies are retrospective, non-randomized, measure inappropriate end points and suffer from selection and overtreatment biases. Unfortunately, these pitfalls are recapitulated in this current paper by Zagoria and colleagues. Specifically, the authors fail to provide pathological data with which to assess the biologic potential of their cohort. Moreover, they report a short median follow-up period of 9.8 months, which is most relevant in nonparametric data. Perhaps the greatest limitation of this study is the measure of success—lack of post-radiofrequency ablation enhancement—which often does not directly correlate with post-ablation biopsies,⁵ and might be unrelated to any survival end point. Although the technical success end point was reached in all patients with SRMs 3.6 cm, this end point was not reached in 47% of patients with tumors >3.7 cm. Finally, the authors' reported complication rate of 8% approaches that reported in trials with more invasive methods.

While this study demonstrates that radiofrequency ablation is technically feasible, it fails to provide insight into its "oncologic efficacy". The ability of radiofrequency ablation to alter the natural history of localized SRMs and affect a survival end point must be more rigorously tested.

Acknowledgments

The synopsis was written by Rachel Murphy, Associate Editor, Nature Clinical Practice.

References

1. Frank I et al. (2005) Independent validation of the 2002 American Joint Committee on cancer primary tumor classification for renal cell carcinoma using a large, single institution cohort. J Urol 173: 1889–1892 | Article | PubMed | ISI |
2. Chawla SN et al. (2006) The natural history of observed enhancing renal masses: meta-analysis and review of the world literature. J Urol 175: 425–431 | Article | PubMed |
3. Crispen PL et al.: Delayed intervention of small sporadic renal masses undergoing active surveillance. Cancer, in press
4. Kunkle DA et al.: Excise, ablate or observe: the small renal mass dilemma. J Urol, in press
5. Weight CJ et al. (2007) MRI is inadequate for monitoring renal tumor destruction following radiofrequency abloation [abstract #497]. J Urol 177

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Subject areas under which this article appears: Urologic oncology (nonprostatic)