Our study of RAPN for completely endophytic renal tumors has yielded significant results, especially in terms of the two primary endpoints (WIT and PSM rate). The observed WIT of 20.3 min (99% CI 18.3–22.3) not only significantly surpassed the historical values associated with cLPN but also remained well below the critical 25-min benchmark crucial for preserved postoperative renal function. The achievement of a 0% in PSM (99% CI 0–5.3%) reflects the oncological efficacy of RAPN, particularly in managing the complexities of completely endophytic tumors. Successfully meeting both primary endpoints clearly demonstrated functional and oncological efficacy of RAPN.

Numerous studies have compared RAPN with cLPN [6,7,8, 16,17,18], and although there is general agreement that RAPN offers superior outcomes, the specific variables where RAPN outperforms cLPN vary between studies. Even among these reports, few are focusing on complex tumors. Overall, the findings contribute to the consensus that RAPN is becoming the standard approach, including complex tumors such as completely endophytic tumors.

There has been a recent trend toward individualized evaluations for surgically challenging tumors. Recent reports have highlighted the shorter WIT in RAPN compared with cLPN for renal hilar tumors, as comparably challenging as completely endophytic tumors [9, 10]. However, studies focusing on completely endophytic tumors, which present even greater surgical challenges, are less common. Observational studies [19,20,21] indicate a WIT of 17–27 min in RAPN for these tumors, which is consistent with our findings. As noted in these study, RAPN, which can be operated in 3D, may be superior to cLPN in highly difficult surgical procedures. This lack of direct comparisons between cLPN and RAPN for completely endophytic tumors underscores the unique contribution and importance of our study. Furthermore, our results highlight the critical role of RAPN in renal function preservation, with WIT averages consistently below the crucial 25-min threshold.

The concept of “trifecta” in partial nephrectomy, initially introduced by Hung et al. [22], encompasses three key outcomes: negative cancer margins, minimal renal functional decrease, and absence of urological complications. It is noteworthy that various papers have modified the latter two criteria. Our study tailored these criteria to evaluate midterm outcomes, specifically defining them as maintaining an eGFR of 90% or above the preoperative level at POD 180 and the absence of significant complications within POD 180.

The trifecta achievement rate of 47.96% (95% CI 38.33–57.74) in our study is notable despite being lower than previously reported rates (61.7–84.1%) [22,23,24]. Considering our 81.6% achievement rate of WIT ≤ 25 min, the difference in trifecta achievement rate between present and previous studies is likely due to differing criteria for renal function. While they set WIT, we based on renal function at POD 180. In studies that expanded the trifecta criteria to include eGFR evaluations several months postsurgery, the reported attainment rates ranged from 54.6 to 67%, slightly higher than that in the present study [24, 25]. This discrepancy suggests that factors beyond early functional success may influence the preservation of midterm renal function. A direct evaluation is difficult to perform because the viewpoints of renal function differ for each paper; however, it seems that 3.2%–50% of patients may have decreased renal function after RAPN [18, 24,25,26].

Our study contributes to understanding the factors influencing postoperative renal function in RAPN. Post-PN renal function had been evaluated by several outcomes such as acute kidney injury [27], split renal functions [28], trifecta or pentafecta [23, 25], or progress of CKD grade [4]. In this study, we evaluated renal function using split renal function, following the previous report [10]. Although preoperative comorbidities such as age, body mass index, and comorbidities are known to impact renal outcomes [29], our analysis focused on surgical factors. We found that the resection weight, WIT, and overall surgical time significantly influenced the postoperative split renal function of operated kidney, Reported surgical factors include the R.E.N.A.L. score, pentafacta, WIT, and bleeding [4, 21, 30]. WIT is often considered to be around 25 min; however, there are also reports that it can have an impact in min [4, 5]. Our findings indicate that although patients with WIT under 25 min exhibit a mix of preserved and decreased renal function, those with WIT over 25 min consistently show decreased renal function, with a few exceptions, suggesting that 25 min is a reasonable threshold, as cases preserving renal function beyond this duration were rare. Several reports have indicated that the R.E.N.A.L. score impact renal function after PN, and in present study, inclusion criteria specifically limited the “R” and “E” factors of the R.E.N.A.L. score. Consequently, these did not exhibit the same impact on renal function as reported previously. In this cohort, the category labeled as “Low risk” within “E” factor was not represented. This absence of the “low risk” group in “E” factor might account for this result. There have been reports suggesting an association with tumor diameter. Resection weight, often dictated by tumor size, was also correlated with achieving negative surgical margins. It is critical to balance the extent of resection with the need to preserve renal function while avoiding excessive healthy renal parenchymal removal. These factors may indicate that enhancing surgical skills and techniques can improve patient outcomes.

Looking forward, while this report has focused on midterm renal function and surgical efficacy, our ongoing research will extend the follow-up period to five years. This long-term follow-up will provide a more comprehensive picture of RAPN outcomes, including sustained renal function and recurrence rates. The forthcoming data will be crucial in further establishing the long-term benefits and potential limitations of RAPN, thereby contributing to the continuous evolution of surgical strategies in renal cancer treatment.

A major limitation of our study is the comparison with historical cLPN data, which may affect the comparative validity. Nevertheless, the use of 99% CIs helps mitigate some uncertainties in our analysis. In addition, renal function after PN has been evaluated using various definitions, and influencing factors may also differ depending on the definition employed. The constant evaluation of renal function will become necessary in the future.