A total of 290 patients were included in the analysis. Supplementary figure 1 shows how these patients were selected for inclusion in the study.
Oncological outcomes in T1a patients using univariate analysis
Baseline characteristics of T1a patients
A summary of the clinical and pathological characteristics of the 238 T1a patients included in the analysis is given in Table 1. RCC histology, Fuhrman grade, age, tumour size, R.E.N.A.L nephrometry score, baseline eGFR and CCI were found to be significantly different between the three groups. The median (IQR) follow-up time was 75.6 (66.8–86.5) months, 106.0 (61.2–135.1) months, and 72 (64.6–99.7) months in CRYO, RFA, and LPN patients, respectively.
Table 1 Baseline characteristics of T1a patients Event-specific outcomes
Totals of 204, 238, 233, and 233 patients were evaluated for CSS, OS, LRFS, and MFS, respectively, with exclusions being for lack of follow-up (LRFS: 5, MFS: 5), and unknown causes of death (CSS: 4) in the LPN group only. Results were comparable between the 3 groups for all 4 endpoints (Figs. 1 and 2). Only two RCC-related deaths were observed: one in the RFA group and one in the LPN group. A total of 31 deaths were observed (CRYO: 13, RFA: 9, LPN: 9). Ten local recurrences were observed (CRYO: 2, RFA: 5, LPN: 3). Five metastatic events were observed (CRYO: 0, RFA: 2, LPN: 3). A total of 72 and 87 patients were evaluated for CRYO and RFA for all outcomes, respectively. A total of 75, 79, 74, and 74 patients undergoing LPN were evaluated for CSS, OS, LRFS, and MFS, respectively.
Oncological outcomes in T1b patients on univariate analysis
A total of 58 T1b patients were included in this study. A summary of their clinical and pathological characteristics are outlined in Table 2. RCC histology, Fuhrman grade, age, tumour size, R.E.N.A.L nephrometry score, baseline eGFR, and CCI were found to be significantly different between the three groups. The median (IQR) follow-up duration is 72.5 (42.0–100.9) months, 59.5 (27.5–99.39) months, and 67.9 (50.8–91.3) months for CRYO, RFA, and LPN, respectively. CSS, OS, LRFS, and MFS are all comparable between patients undergoing CRYO, RFA, or LPN (Figs. 1 and 3). The details of the results are outlined in the supplementary appendix.
Table 2 Baseline characteristics of T1b patients Post-operative complications
The rate and severity of post-operative complications for all three modalities were found to be similar in both cT1a (CRYO: 11.1%, RFA: 18.4%, LPN: 14.1%) and cT1b patients (CRYO: 19.4%, RFA: 15.4%, LPN: 7.7%). Both logistic regression and multinomial logistic regression did not show significant difference between the three groups’ rate and severity of complications (Supplementary Table 1 and 2). A summary of all complications occurring during the study period are reported in Supplementary Table 3.
Change in renal function
The post-operative eGFR and change in eGFR peri-operatively of T1a and T1b patients undergoing CRYO, RFA, and LPN are shown in Table 3. Only small changes in eGFR were found in patients undergoing CRYO and RFA, as compared to substantial falls in eGFR in LPN patients (Wilcoxon matched pairs signed rank sum Z and p-values; CRYO: 3.0, 0.003, RFA: 2.4, 0.02, LPN: 6.0, < .0001). When comparing the change in renal function peri-operatively using the Wilcoxon 2-sample rank sum test, in both T1a (Z = 4.1, p < .0001) and T1b (Z = 2.5, p = .01) patients, those undergoing IGA had a significantly smaller median change in eGFR compared to LPN (Table 3).
Table 3 Peri-operative change in eGFR in T1a and T1b patients undergoing image-guided cryoablation, RFA, and PN Results of propensity-score matching and multivariate analysis
Initially, it was intended to explore the propensity score matching approach, as described in the “Methods” section. However, this proved to be infeasible due to large differences in baseline factors between the treatment groups, most substantially in age (Supplementary Figure 4; Tables 1 and 2). Further details, results, and explanation are given in supplementary Figures 2 and 3. Therefore, as described in the “Methods” section, the Cox multivariate method was used to adjust for these imbalances and compare the treatment arms (Table 4). As events are relatively scarce in this study, sensitivity analyses were performed by replacing an event with censoring at that time (results not presented). Minimal differences to the results presented were observed for all of the outcomes, demonstrating that the results are relatively insensitive to such small changes, and are therefore relatively robust. Certainly, the overall findings would be unchanged as a result of a single patient having a different outcome.
Table 4 Oncological outcomes in T1a and combined T1a/T1b patients in multivariate Cox proportional hazards model In univariate Kaplan-Meier analyses, IGA and LPN were shown to have comparable LRFS. However, given that the CRYO and RFA groups consist of patients with considerably worse prognostic factors, after multivariate adjustment, CRYO and RFA appear to be superior to LPN for LRFS. The magnitude of the effect in the two ablative therapy groups is almost identical (see Supplementary Figure 5) so a combined group analysis, stratified by group, was performed, demonstrating ablative therapies to be superior to LPN for LRFS (HR 0.006, 95% CI 0.00–0.15, p = 0.002). Note that the RFA/LPN comparison reaches statistical significance on its own (Table 4; p = 0.003), and, although the CRYO/LPN result is not statistically significant (Table 4, p = 0.087), this is largely a result of paucity of patient and event numbers. Although effect sizes (HR) appear to be substantial for statistically significant outcomes (LRFS, MFS), suggesting extreme advantage to IGA patients, they are unlikely to reflect real effect sizes due to a combination of the extreme selection bias. Finally, the lower 90% confidence interval on the hazard ratio is less than 1 for CRYO (Supplementary Table 5), which demonstrates at least 90% confidence that CRYO is as good as LPN for LRFS. For clarity, characteristics of all patients with T1a tumours and subsequent local recurrences are shown in Table 5.
Table 5 Characteristics of all patients with T1a tumour and local recurrences