Thermo-ablation of Renal Allograft Tumors: Every Patient, and Every Nephron, Counts.

De novo tumors in renal allografts are uncommon but present a challenging clinical scenario. Historically, the gold-standard treatment for renal tumors involves nephrectomy. In the setting of renal allograft tumors, however, nephrectomy results in kidney graft loss. Additionally, the technical complexity of a reoperative field along with significant patient comorbidities may result in surgical nephrectomy carrying prohibitive risk. Less invasive methods of treating renal tumors, such as thermos-ablation, can be considered acceptable alternatives to nephrectomy; data are sparse, however, about their use in tumors found in transplanted kidneys. In this issue of Transplantation, Bodard et al1 evaluate a single institutional experience utilizing percutaneous, nephron-sparing thermoablative techniques for de novo allograft tumors in transplanted kidneys. Presenting the largest series of patients available in the literature to date, 26 tumors in 19 patients were treated with thermoablative techniques. Twenty-two tumors averaging 22 mm (range 7–41 mm) were treated with radiofrequency ablation, 3 with microwave ablation, and 1 with cryoablation. In terms of oncologic outcomes, complete ablation was achieved in 25 of 26 tumors at a median follow-up of 35 mo (range: 15–69 mo). One tumor recurred 42 mo following initial treatment requiring repeat ablation. No metastatic disease or cancer-specific mortality was observed during the study follow-up. No intraprocedural complications were observed, whereas 4 patients had mild/moderate postprocedural complications according to the Common Terminology Criteria for Adverse Events. Overall, thermo-ablation was not associated with a significant change in renal function up to 1 y, although 3 patients with baseline estimated glomerular filtration rate (eGFR) <30 mL/min and 1 with an eGFR of 52 mL/min progressed to end-stage kidney disease during study follow-up. Conclusions derived from the Bodard et al1 study are limited by those of a single center, retrospective review of a 19-patient cohort. Nevertheless, it represents a valuable addition to a small body of literature assessing nephron-sparing ablative treatments to treat renal allograft tumors. Previously published studies in this domain include case reports, small case-series, and reviews of the former 2. In these studies, thermo-ablation has been largely performed in patients with advanced age, comorbid conditions, and smaller (mainly T1a) lesions; in these settings, it has shown to be effective in preventing early local recurrence.2,3 Thermo-ablation also appears to achieve comparable local control to partial nephrectomy, an alternative approach to nephron-sparing treatment of renal allograft tumors.4 The oncologic outcomes presented in the Bodard study are concordant with previously published literature and reinforce thermo-ablation as an effective means of treating small tumors in renal allografts. An overarching deficiency in the literature, however, is a lack of long-term follow-up that would allow for sufficient time to detect local recurrence and metastatic disease. As the authors note, the study’s 34-mo median follow-up (range 15–69 mo) is comparable to previous studies and does not provide substantive data about long-term outcomes. Although percutaneous thermo-ablation demonstrates promise as an effective nephron-sparing, minimally invasive approach to treating renal allograft tumors, longer follow-up is essential to understand its therapeutic potential. The incidence of de novo renal allograft tumors is around 0.19%,5 which helps explain the small sample sizes and lack of long-term follow-up consistently seen in studies assessing thermo-ablation as a treatment of renal allograft tumors. When facing an uncommon scenario such as this, clinical practice can be guided by surrogate data that best approximate the conditions in question. Fortunately, in this case, there exists a larger body of literature assessing thermo-ablation as a means of treating tumors in native kidneys. The REPART Study-UroCCR71 provided a propensity score-matched analysis of 81 patients treated with either percutaneous ablation or surgical resection for locally recurrent disease following partial nephrectomy, finding no significant difference between treatments in local recurrence or distant metastasis.6 Conversely, a propensity matched study of cT1a renal masses by Bianchi et al7 found that ablation was independently associated with disease recurrence on competing risk analysis. Here, 5-y disease-free survival was greater in patients treated with partial nephrectomy (92.8%) than those receiving local ablative treatments (80.5%, P = 0.02).7 Although the data about oncologic outcomes in renal allograft tumors treated with thermo-ablation at first glance seem more consistent, the available literature in treatment of native kidney tumors demonstrates the need for additional studies and longer-term follow-up. Thermoablative therapy offers the attraction of providing a minimally invasive, nephron-sparing treatment to preserve renal allograft function. Achieving a complete tumor response with the preservation of the affected kidney, however, requires careful balance. Too little treatment may promote carcinogenesis, with studies in murine models demonstrating that incomplete ablation carries the potential risk of increased proliferation of residual tumor cells.8 Too much treatment, conversely, may promote renal insufficiency—of the 19 patients undergoing thermoablative treatment in the Bodard et al study, 4 progressed to end-stage renal disease, 3 of whom had pretreatment eGFR <30 mL/min. This 21.05% observed incidence of renal failure aligns with prior studies that reported upward of 30% of patients treated with thermo-ablation progressing to end-stage renal disease, all of whom were stage 4 chronic kidney disease.9 Ultimately, the utility of thermo-ablation in treating early stage tumors must be carefully considered, especially when considering that active surveillance remains an acceptable management strategy.10 Bodard et al’s single institutional experience using thermo-ablation to treat de novo renal allograft tumors serves several important purposes. With the largest cohort available in the literature to date, the findings of the study help solidify the role of thermo-ablation as a safe alternative to nephron-sparing surgical tumorectomy. The study also further emphasizes the ongoing lack of long-term oncologic outcomes necessary to better define the ability of thermo-ablation in preventing local recurrence and distant metastasis. Finally, Bodard et al highlight the importance of optimally utilizing thermoablative treatments, in which too little can come at the expense of oncologic treatment, and too much can come at the expense of the renal allograft. In a clinical scenario requiring careful consideration of both tumor and allograft, future studies will utilize and expand upon the findings set forth in this article to continue to better define the role of thermo-ablation in the treatment of renal allograft tumors.