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Sawada et al. Mini-invasive Surg 2021;5:6 I http://dx.doi.org/10.20517/2574-1225.2020.100 Page 9 of 11

In contrast, cold ischemia should be selected in cases where the tumor is anatomically complex and
when the ischemia time is expected to be prolonged. The shorter the cold ischemia period, the better the
postoperative renal function is. Considering this, OPN should be prioritized when it can ensure a faster
and more accurate resection and renorrhaphy in cases with complex tumors.

In this study, 73 cases in RAPN and 13 cases in OPN were excluded by PSM. Excluded cases included
patients in the RAPN group who were relatively older and had a higher BMI and lower RENAL score, and
those in the OPN group who were relatively younger and had larger tumor diameters. Therefore, the results
of this study may not necessarily apply to such excluded cases.

In recent years, there has been an increasing number of reports confirming that RAPN can be safely used
for the resection of complex or large tumors [6,37-39] . In this study and other reports, RAPN was shown to
have equivalent or better outcomes compared with OPN in many aspects of the perioperative results.
This suggests that RAPN is a viable surgical option for the resection of complex and large tumors in
the future. However, this hypothesis is based on the premise that the surgeon has sufficient technical
proficiency in robotic surgery. Therefore, it is necessary to select an appropriate surgical method according
to the surgeon’s and the institution’s level of proficiency in robotic surgery, taking into consideration the
complexity of the tumor and patient factors.

This study had several limitations. First, the sample size of the study was relatively small. Furthermore,
it was nonrandomized and retrospective in nature; thus, it was subject to the inherent limitations of a
retrospective analysis of observational data, possibly making it difficult to obtain original results. Second,
the results of the PSM in this study may be generalized only among those within the propensity score
range included in the paired analysis and may not be applicable to those outside this range. Third, different
surgeons were involved in this study, which might be seen as a source of biases because different phases
of different learning curves were included and might have influenced the results. Fourth, the timing of the
surgery (i.e., pre- or post- 2016) was another limitation because more recent cases underwent RAPN and
older cases predominantly underwent OPN, as RAPN has been covered by insurance in Japan since 2016.
Finally, this study used data collected from a single center with a high incidence of kidney cancer and
cannot be generalized to providers with different characteristics.

In conclusion, this study compares the perioperative outcomes of RAPN and OPN performed at a single
institution. Our results indicate that RAPN with warm ischemia preserves renal function equally well or
better than does OPN with cold ischemia in selected cases with short ischemic times.

DECLARATIONS
Acknowledgments
The authors would like to thank Enago (www.enago.jp) for the English language review.

Authors’ contributions
Made substantial contributions to the conception and design of the study and performed data analysis and
interpretation: Sawada A
Performed data acquisition as well as provided administrative, technical, and material support: Takahashi
T, Kono J, Masui K, Sato T, Sano T, Goto T
Drafted the article or revised it for critically important intellectual content and approved the final version:
Kobayashi T, Akamatsu S, Ogawa O

Availability of data and materials
Not applicable.