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The number of incidentally discovered renal masses is increasing because of the widespread use of cross-sectional imaging. Most of these masses are small, slow-growing and confined to the kidney at the time of diagnosis . Radical nephrectomy (RN) has historically been the ‘gold standard’ treatment in these cases, but has been shown to carry an increased risk of chronic kidney disease (CKD) and cardiac events compared with nephron-sparing approaches [2, 3]. Currently, nephron-sparing surgery, such as partial nephrectomy (PN), is the standard of care for small renal masses , but this surgery can be technically challenging and may be associated with significant peri-operative complications and morbidity [5, 6]. With this in mind, minimally invasive nephron-sparing techniques such as cryoablation and radiofrequency ablation (RFA) have been used in an effort to decrease complications, shorten the convalescence period and reduce ischaemic insult.
Based on the current AUA guidelines for T1 renal masses, thermal ablation treatment is reserved for tumours <4 cm in older patients with significant comorbidities. Within the three-tiered system implemented by the AUA, thermal ablation treatments have achieved a ‘statement of recommendation’ as a nephron-sparing strategy for unhealthy patients with a T1a renal mass . For healthy patients, the panel stated that thermal ablation was ‘an option’, their lowest strength statement. The panel cited the relative lack of large cohorts and long-term oncological data as reasons for their conclusions. To help address these shortcomings, we report oncological and renal function outcomes after RFA for T1a renal masses in healthy patients with long-term follow-up (median of 5 years).
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Of the 354 patients who underwent RFA within the study period, 117 patients had an ASA score of 1 or 2. Of these, 54 patients had follow-up ≥3 years. Of the remaining patients, two patients were excluded because RFA was performed for PN recurrence. This left a total of 52 patients with ASA scores of 1 (n = 2) or 2 (n = 50) who were included in the analysis. Patient characteristics are shown in Table 1. One patient had bilateral tumours and five had multiple tumours. Laparoscopic RFA was performed for 24 tumours and percutaneous RFA for 34 tumours. The patients' median (interquartile range [IQR]) age at the time of ablation was 57 (51–63) years. The mean (sd) tumour size was 2.2 (0.8) cm. A slight majority (52.5%) of the tumours were exophytic. A procedural biopsy was performed in 55 tumours (95%) and RCC was confirmed in 41 (70%) tumours.
Table 1. Patient demographics and tumour characteristics
|No. of patients||52|
|Male (%)||35 (67.3)|
|Female (%)||17 (32.7)|
|No. of masses||58|
|Median (IQR) age, years||57 (51–63)|
|Median (IQR) follow-up, months||60.1 (48–90)|
|Mean (sd) tumour diameter, cm||2.2 (0.8)|
|Treated side, n (%)|| |
|Tumour location, n (%)|| |
|Approach, n (%)|| |
Of the 58 treated renal masses, no incomplete ablations were identified. Local tumour recurrence was observed in three patients, all with RCC and all recurring within 3 years. No patients developed metastatic disease. Of the three patients with local recurrence, all underwent RN, two after re-ablation failure. One patient who underwent RN for persistent peripheral enhancement of CT showed no viable RCC, but rather a giant cell reaction.
The median (IQR) follow-up was 60 (48–90) months, with a 5- and 10-year recurrence-free survival of 94.2% (Figure 1). No patient developed metastatic disease and none died from RCC, which gave metastatic-free and cancer-specific survival rates of 100%. Three patients died in the follow-up period, but none from RCC. One died from congestive heart failure complications, one from an undefined cardiovascular event and one from acalculous cholecystitis. The 5- and 10-year overall survival rates were 95.7 and 91.1%, respectively (Figure 2).
Renal function outcomes are shown in Table 2. The paired change in eGFR before (106.3 mL/min/m2) and after RFA (99.2 mL/min/m2) was not significantly different (P = 0.058). Eight patients had CKD stage progression and one patient had CKD stage improvement during follow-up.
Table 2. Estimated GFR of patients before and after treatment at a mean of 40 months after RFA
| ||Pre-treatment eGFR (sd)||Post-treatment eGFR (sd)||P|
|All patients||106.3 (48.8)||99.2 (39.2)||0.058|
|CKD classification|| || || |
|4 and 5||0||0|| |
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Renal tumour ablation has conventionally been reserved for patients with small tumours who are in general poor health, but the use of cryoablation and RFA has increased in recent years. Reasons for this increase may include the ease of use and relative lack of complications, along with reported excellent short- and intermediate-term oncological and renal function outcomes in selected patients [9, 10]. Nevertheless, RFA studies demonstrating oncological efficacy are limited by sample size and relatively short follow-up and these limitations are among the reasons that PN remains the preferred method of nephron-sparing treatment [4, 11].
When compared with that of PN, the oncological equivalence of RFA varies between reports and is largely based on cohort selection. In a large population-based study, Whitson et al. found there to be significant differences between tumours treated by PN and thermally ablated tumours in terms of disease-free survival . This study, however, did not directly compare RFA with PN, rather it included RFA, cryoablation and other unspecified types of ablation. Furthermore, there were also significant differences between the study cohorts, with larger tumours and older patients included in the ablative group. Lastly, the era in which the ablative therapy was performed was considered by those authors to be a confounding variable, with the outcomes of more contemporary ablations rivaling those for PN. In a study comparing matched cohorts for PN and RFA, Olweny et al.  reported 5-year recurrence-free survival and cancer-specific survival to be similar, but that study was limited by small numbers in each arm (<50 patients) and a short mean follow-up in the RFA arm (30 months). Although the present study did not have a matched PN group of patients, it did show similar long-term results to those published for PN (Figure 1). Although local recurrence was detected in three patients, all were successfully retreated and all remained without evidence of disease on last follow-up. Furthermore, no patients developed metastasis or died from RCC.
When treating small renal masses with ablation techniques, their great dependence on tumour size should be considered. The current guidelines use a 4 cm threshold to distinguish between T1a and T1b stages. Despite studies confirming that outcomes for T1b tumours treated with RFA are significantly worse than those for T1a tumours , this may not be the most clinically relevant distinction when considering the technical success of RFA. A recent paper by Best et al.  showed a significant improvement in RFA success and disease-free survival in tumours <3 cm. In that study, patients with a tumour <3 cm had a 3-year 96% disease-free survival rate, while those with tumours >3 cm had a 3-year disease-free survival rate of 79%. Other studies have reported similar findings, with 3 cm seeming to be a clinically relevant threshold for tumour size for the success of both RFA and cryotherapy [16, 17]. In the current study, the only tumours that showed recurrence were >3 cm, again suggesting the sensitivity of RFA to tumour size, even within the T1a classification.
While oncological outcomes are of primary concern when treating RCC, recent evidence suggests that preservation of renal function is paramount as this can improve overall survival in this population. Thompson et al.  reported an age-dependent increased relative risk of mortality in patients undergoing RN vs PN. The age dependence was noted only in patients <65 years old, which would imply that a significant life expectancy after treatment was needed for the deleterious effects of RN to be seen. Examining this relationship further, Lucas et al.  compared renal function outcomes for several treatment methods and, on multivariate analysis, found that a significant increased risk for the development of CKD was associated with PN (hazard ratio 10.4) and RN (hazard ratio 34.3) compared with RFA. While this study did not specifically look at mortality, the development of CKD was used as a surrogate for potential morbidity as it has been linked to adverse cardiac events and death . While no comparative group was available for the present study, we found that renal function based on eGFR measurements was preserved after RFA and included the three patients who underwent RN for suspected recurrence. Of the eight patients with CKD stage progression, six had a change in eGFR of <10 mL/min/m2, indicating that these patients were simply near a CKD cutoff point at the time of ablation. Furthermore, the patient population was relatively young; >75% of the patients in our study were aged <65 years. As suggested by Thompson et al. , this young, healthy population may gain the most benefit from nephron-sparing treatment. As such, the renal function data reported in the present study, in combination with the oncological outcomes, suggest that RFA of small renal tumours (especially those <3 cm) could be considered as a treatment option in younger, healthy patients. We acknowledge that this is the first long-term study of its kind and its results will require confirmation in a larger cohort. Nevertheless, our data may be useful in counselling healthier patients who want to avoid surgery or in whom PN may be exceedingly difficult, but where a nephron-sparing approach is preferred.
Several limitations are worth noting in this study, one being the use of the ASA score as a surrogate for patient health. Although this may be a somewhat simplistic system, previous studies have shown ASA score to correlate with postoperative patient outcomes . Only three patients died from causes other than RCC over an extended study period (Figure 2), and those who did die were all >70 years, which validates our population as healthy at the time of RFA. Another limitation is the follow-up period. Despite being one of the longest reported series, RCC recurrences have been described in up to 3-6% of patients after 5 years [20, 21] and, although no recurrences were observed in any patient after 3 years in this series, late recurrence may be an important factor when considering healthy patients with prolonged life expectancy. Lastly, as this was a retrospective study, selection bias is an issue. Approximately 33% of the patients treated with RFA at our institution had ASA scores of 1 or 2, demonstrating the current trend of reserving this technique for patients with generally worse comorbidities and a shorter life expectancy. Prospective studies enrolling younger, healthy patients are needed in this field, with the caveat that patient counselling in this population must be performed carefully and thoroughly.
In conclusion, according to the available long-term oncological and renal function outcomes, the treatment of clinical T1a renal cancer with RFA in healthy patients appears favourable. Before recommending this as a treatment alternative in this population, larger confirmatory studies with comparable follow-up are needed.