Methods. Surgery. Patient population. Volumetric analysis. Statistical analysis. Ethical approval

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1 International Journal of Urology (2018) 25, doi: /iju Original Article: Clinical Investigation Robot-assisted laparoscopic partial nephrectomy versus laparoscopic partial nephrectomy: A propensity score-matched comparative analysis of surgical outcomes and preserved renal parenchymal volume Hidekazu Tachibana, 1 Toshio Takagi, 1 Tsunenori Kondo, 2 Hideki Ishida 1 and Kazunari Tanabe 1 1 Department of Urology, Tokyo Women s Medical University, and 2 Department of Urology, Tokyo Women s Medical University, Medical Center East, Tokyo, Japan Abbreviations & Acronyms AKI = acute kidney injury ASA = American Society of Anesthesiologists BMI = body mass index DM = diabetes EBL = estimated blood loss egfr = estimated glomerular filtration rate HTN = hypertension LPN = laparoscopic partial nephrectomy OT = operative time PLOS = postoperative length of hospital stay PN = partial nephrectomy POD = postoperative day PS = Eastern Cooperative Oncology Group Performance Status RAP = renal artery pseudoaneurysm RAPN = robot-assisted partial nephrectomy RENAL-NS = RENAL nephrometry score SM = surgical margin WIT = warm ischemia time Correspondence: Toshio Takagi M.D., Ph.D., Department of Urology, Tokyo Women s Medical University, 8-1 Kawada-cho, Shinjuku-ku, Tokyo , Japan. t.takagi1192@gmail.com Received 13 July 2017; accepted 27 December Online publication 4 February 2018 Objectives: To compare surgical outcomes, including renal function and the preserved renal parenchymal volume, between robot-assisted laparoscopic partial nephrectomy and laparoscopic partial nephrectomy using propensity score-matched analyses. Methods: In total, 253 patients, with a normal contralateral kidney, who underwent laparoscopic partial nephrectomy (n = 131) or robot-assisted laparoscopic partial nephrectomy (n = 122) with renal arterial clamping between 2010 and 2015, were included. Patients background and tumor factors were adjusted by propensity score matching. Surgical outcomes, including postoperative renal function, complications, warm ischemia time and preserved renal parenchymal volume, evaluated by volumetric analysis, were compared between the surgical procedures. Results: After matching, 64 patients were assigned to each group. The mean age was years, and the mean tumor size was 22 mm. Approximately 50% of patients had low complexity tumors (RENAL nephrometry score 4 7). The incidence rate of acute kidney failure was significantly lower in the robot-assisted laparoscopic partial nephrectomy (11%) than laparoscopic partial nephrectomy (23%) group (P = 0.049), and warm ischemia time shorter in the robot-assisted laparoscopic partial nephrectomy (17 min) than laparoscopic partial nephrectomy (25 min) group (P < ). The preservation rate of renal function, measured by the estimated glomerular filtration rate, at 6 months post-surgery was 96% for robot-assisted laparoscopic partial nephrectomy and 90% for laparoscopic partial nephrectomy (P < ). The preserved renal parenchymal volume was higher for robot-assisted laparoscopic partial nephrectomy (89%) than laparoscopic partial nephrectomy (77%; P < ). The rate of perioperative complications, surgical margin status and length of hospital stay were equivalent for both techniques. Conclusions: Robot-assisted laparoscopic partial nephrectomy allows to achieve better preservation of renal function and parenchymal volume than laparoscopic partial nephrectomy. Key words: kidney neoplasm, nephrectomy, outcome, robotics. Introduction PN is the gold standard for the resection of small renal masses, and is preferred over radical nephrectomy, providing equivalent oncological outcomes, but with greater preservation of renal function. 1 4 In the era of minimally invasive surgery, RAPN is being increasingly used, as it enables precise resection and reconstruction compared with LPN. Hence, the indications for RAPN have been expanded to the treatment of large and more complex tumors, including those located in the renal hilum. Theoretically, RAPN is superior to LPN in terms of preserving renal function, possibly due to the fact that the precise and relatively quick maneuver allows preservation of a greater volume of renal parenchyma and/or a shorter duration of WIT. Furthermore, these benefits of RAPN on renal function are obtained with surgical outcomes that are similar or superior to those obtained with LPN. 5 8 Choi et al. compared perioperative outcomes of RAPN and LPN using a meta-analysis, and showed that RAPN was associated with more favorable results than LPN, including a lower conversion rate to open 2018 The Japanese Urological Association 359

2 H TACHIBANA ET AL. or radical surgery, greater preservation of renal function, shorter length of hospital stay and shorter WIT. 8 The superiority of RAPN over LPN with regard to renal function might result from a shorter WIT and/or enhanced preservation of the normal parenchyma. However, although the shorter WIT for RAPN compared with LPN has been well-described, the important feature of differences in the volume of renal parenchyma that is preserved between RAPN and LPN has not been well evaluated to date. In the present study, we compared surgical outcomes and the volume of preserved vascularized renal parenchyma, calculated by volumetric analysis, between RAPN and LPN, using a propensity score-matching analysis to specifically evaluate differences in surgical precision of excision and reconstruction. Methods Patient population Institutional review board approval was obtained to carry out a retrospective analysis of patient data. Patients who underwent LPN or RAPN for renal tumors between January 2010 and January 2015 were included in this study. Patients with an anatomically or functionally solitary kidney and those without enhanced computed tomography images, before and after surgery, were excluded. In total, 251 patients (LPN, n = 131; RAPN, n = 122) were eligible for the study. The clinical and pathological parameters for each patient were extracted from our electronic medical chart database. Tumor complexity was determined using the RENAL-NS. The following patient-related variables were included in our analysis: age, PS, sex, BMI, presence of DM, presence of HTN, the ASA score, tumor complexity and the preoperative egfr. Perioperative surgical outcomes were defined as follows: preserved volume of vascularized parenchymal mass, preserved egfr, operative time, WIT, EBL, surgical margin status, perioperative complications and PLOS. Postoperative complications were defined according to the Clavien Dindo classification. 9 Urine leakage was defined as a persistent drain output, having a chemical composition consistent with urine, >48 h after PN. 10 The postoperative global renal function was assessed using the nadir egfr postoperatively, at 3 and 6 months post-surgery. egfr was calculated using the Modification of Diet in Renal Disease 2 equation, further modified for Japanese patients as outlined by the Japanese Society of Nephrology (egfr = serum creatinine mg/ dl age 9 [0.739 if female]). 11 Postoperative acute kidney injury was defined as a 25% decrease between the pre- and postoperative nadir egfr, measured on POD 1 7. The selection of the surgical approach, RAPN or LPN, was dependent on the period and patient preference. With regard to the period, we have been carrying out robot-assisted surgery since 2013; therefore, between 2010 and 2013, all LPN procedures were carried out without robotic technology. Furthermore, the cost is greater for RAPN than LPN, which included the patients decision with regard to the selected approach. To minimize the effects of selection bias on measured between-group differences, the following variables were adjusted using 1:1 propensity score matching: age, sex, BMI, presence of HTN, presence of DM, ASA score, preoperative egfr, tumor size and tumor complexity. Ethical approval All procedures involving human participants in this study were carried out in accordance with the ethical standards of the institutional and/or national research committee, and with the 1964 Helsinki declaration and its later amendments, or comparable ethical standards. IRB approved number: Surgery All procedures were carried out by three specialized surgeons. Both LPN and RAPN were carried out using a transperitoneal approach in most cases, with a retroperitoneal approach used in 15 LPN cases and six RAPN cases. LPN and RAPN procedures were carried out using previously described techniques For LPN, four or five ports were placed, whereas RAPN procedures were carried out using da Vinci devices (three or four arms, at the surgeon s preference, and two assistant ports). A total renal arterial clamping technique, without cooling the kidney, was used in all cases. The kidney was mobilized within Gerota s fascia, except for the perirenal fat around the tumor. We used an ultrasound probe to obtain the location, depth and borders of the tumors to determine the excision margins. Selective clamping of the renal artery was carried out in most cases. Renal tumors were resected with a 2 5-mm renal parenchyma margin. After tumor resection, an inner running suture was placed to close visibly bleeding vessels. Incidental openings of the renal sinus or collecting system were closed with absorbable sutures. For the outer sutures, a running suture was placed to approximate the renal parenchyma, with or without a bolster in the defect. Volumetric analysis Three-dimensional dynamic enhanced abdominal computed tomography images, obtained pre- and postoperatively with a Toshiba Aquilion 64 multidetector scanner (Toshiba, Tochigi, Japan), were used for volumetric analysis. The vascularized renal parenchyma, excluding perirenal fat, the collecting system and cyst, were measured (Fig. 1). The volume was estimated from axial scans in the venous phase reconstructed at 5-mm intervals. Manual scripting was used to define the area of interest at each 5-mm level, with the defined areas subsequently summed to yield the total volume. One urologist, who was not involved with the surgery, measured the renal parenchymal volume. Statistical analysis All statistical analyses were calculated with JMP 11 (SAS Institute, Cary, NC, USA). Between-group differences were evaluated using Student s t-test for continuous variables, v 2 - test for unordered categorical variables and Mann Whitney U-test for ordinal categorical variables. A P-value <0.05 was considered statistically significant The Japanese Urological Association

3 Parenchymal preservation in partial nephrectomy Preoperative CT Postoperative CT Fig. 1 Vascularized parenchymal volume, measured by freehand scripting, to accurately remove the volume of the tumor, collecting system and renal cyst. Results The relevant characteristics of the 253 patients forming our study group, before matching, are summarized in Table 1. There were no significant differences between the LPN and RAPN groups with regard to the distribution of age, sex, ASA score, BMI, and presence of HTN and DM. Compared with the LPN group, the RAPN group had a larger mean tumor size (27 mm vs 20 mm, P < 0.001), lower preoperative egfr (65 ml/min/1.73 m 2 vs 71 ml/min/1.73 m 2, P = 0.002) and higher RENAL-NS (6.8 vs 6.0, P < 0.001). After matching, 64 patients were allocated to each operative group. The mean age was years, and 17 20% of patients had DM. The mean tumor diameter was 22 mm, with approximately 95% of patients having low- or intermediate-complexity tumors (RENAL-NS 4 9). The mean preoperative egfr was ml/min/1.73 m 2. Comparisons of surgical outcomes between the LPN and RAPN groups are reported in Table 2. After propensity score matching, the incidence rate of AKI was 23% in the LPN group and 11% in the RAPN group (P = 0.049). The preservation rate of egfr was greater for the RAPN than the LPN group at 3 months (96% vs 90%, respectively, P = ) and 6 months (95% vs 90%, respectively, P = 0.02) after surgery. The mean operative time was longer for the LPN (204 min) than the RAPN (186 min) group (P = 0.01). WIT was significantly shorter in the RAPN (18 min) than the LPN (24 min) group (P < ). Other surgical outcomes, including EBL, surgical margin status, incidence rate of complications and PLOS were not significantly different between the two groups. Between-group differences in the preserved renal parenchymal volume are reported in Table 3. The mean preoperative normal parenchymal volume was 154 cc in the LPN group and 145 cc in the RAPN group (P = 0.09). In contrast, the mean postoperative renal parenchymal volume was lower in the LPN (118 cc) than the RAPN (130 cc) group (P = 0.035). The preservation rate of parenchymal volume was significantly higher in the RAPN (89%) than the LPN (77%) group (P < ). Discussion LPN is a difficult technique to carry out for highly complex tumors because of the limitations in forceps handling and the overall high technical demand of the procedure. Consequently, RAPN has been increasingly used, as it facilitates forceps handling, which leads to precise resection and reconstruction for partial nephrectomy. With the refinement of techniques for robotic surgery, the indication for RAPN is increasingly expanding to include large and more complex tumors located in the renal hilum. 5,15 17 We have preferentially adopted the RAPN technique in our institution since 2013, and the number of patients undergoing RAPN is also increasing in accordance with our experience. 18 In the present study, we showed that RAPN provided a better preservation of renal function and renal parenchymal volume than LPN, with similar surgical margin status and rate of perioperative complications for both techniques. The superiority of RAPN over LPN has previously been reported, and includes a clear, three-dimensional view of the region of interest and fine movement of surgical instruments, with both of these factors likely contributing to the lower incidence of complications, such as open conversion, postoperative bleeding, urine leakage, shorter ischemia time and better preservation of renal function. 5,7,19,20 In several reports, shortened WIT in RAPN has been associated with better preservation of renal function. 7,16,21 The WIT in the present study was similarly shorter for the RAPN (17 min) than the LPN (25 min) procedure (P < ), after propensity matching, suggesting that this difference in ischemia time might contribute to better renal function outcome in the RAPN than LPN group. Only a few previous studies have compared the preservation of renal parenchymal volume between different surgical approaches. Woldu et al. compared renal parenchymal mass preservation among open PN, LPN, RAPN and thermal ablation procedures for 150 cases of small renal masses. 21 A lower mean loss of renal parenchymal volume was reported for thermal ablation compared with PN. However, no differences were identified between modalities of thermal ablation (cryoablation vs radiofrequency) or between approaches to PN (open PN vs LPN vs RAPN). Of note, the study by Woldu et al. included relatively small patient samples (30 cases for RAPN and 30 cases for LPN), with no adjustment for patient- and tumor-related characteristics. Therefore, the possibility of a selection bias according to surgical approaches in their study cannot be discounted. In the present study, we reported a significantly higher renal parenchymal volume preservation for RAPN than LPN 2018 The Japanese Urological Association 361

4 H TACHIBANA ET AL. Table 1 Patient characteristics Pre-matching Post-matching LPN (131) RAPN (122) P LPN (64) RAPN (64) P Mean age, years (SD) Male, n 87 (66%) 95 (78%) (73%) 48 (75%) 0.83 Mean BMI, kg/m 2 (SD) HTN (n) 53 (40%) 56 (50%) (42%) 25 (39%) 0.71 DM (n) 22 (17%) 22 (18%) (20%) 11 (17%) 0.65 ASA score (n) 1 29 (22%) 30 (25%) (23%) 17 (27%) (72%) 87 (71%) 46 (72%) 45 (70%) 3 7 (5%) 5 (4%) 3 (5%) 2 (3%) Tumor complexity (n) Low (4 6) 83 (63%) 50 (41%) (50%) 34 (53%) 0.87 Intermediate (7 9) 45 (34%) 64 (52%) 29 (45%) 28 (44%) High (10 12) 3 (2%) 8 (7%) 3 (5%) 2 (3%) Mean tumor size, mm (SD) < E(n) 1 60 (46%) 35 (29%) (30%) 23 (36%) (48%) 78 (64%) 37 (58%) 35 (55%) 3 8 (6%) 9 (7%) 8 (13%) 6 (9%) N(n) 1 80 (61%) 48 (39%) < (45%) 32 (50%) (21%) 20 (16%) 19 (30%) 17 (27%) 3 23 (18%) 54 (44%) 16 (25%) 15 (23%) L(n) 1 63 (48%) 54 (44%) (44%) 29 (45%) (19%) 24 (20%) 12 (19%) 16 (25%) 3 43 (33%) 44 (36%) 24 (38%) 19 (30%) Mean preoperative egfr, ml/min/1.73 m 2 (SD) Table 2 Surgical outcomes Pre-matching Post-matching LPN (131) RAPN (122) P LPN (64) RAPN (64) P Mean preoperative egfr, ml/min/1.73 m 2 (SD) Mean postoperative nadir egfr, ml/min/1.73 m 2 (SD) Incidence of AKI (>25% decrease in egfr) 28 (21%) 9 (7%) (23%) 7 (11%) Mean postoperative egfr 3 months, ml/min/1.73 m 2 (SD) Mean preservation rate of egfr 3 months, % (SD) Mean postoperative egfr 6 months, ml/min/1.73 m 2 (SD) Mean preservation rate of egfr 6 months, % (SD) < Mean OT, min (SD) Mean ischemia time, min (SD) < < Mean EBL, ml (SD) SM negative (n) 131 (100%) 122 (100%) 1 64 (100%) 64 (100%) 1 Perioperative complication (n) Overall 34 (26%) 28 (23%) (23%) 10 (16%) 0.26 Clavien (12%) 10 (8%) (9%) 5 (8%) 0.75 Clavien 3 18 (14%) 18 (15%) (19%) 9 (14%) 0.33 Postop bleeding (n) 4 (3%) 0 (0%) (3%) 0 (0%) 0.15 Asymptomatic RAP (n) 13 (10%) 16 (13%) (14%) 7 (11%) 0.59 Urine fistula, G3 (n) 2 (2%) 0 (0%) (3%) 0 (0%) 0.15 Mean PLOS, days (SD) Mean follow-up period, months (SD) < (89% vs 77%, P < ) after propensity score matching. Although we did adjust for patient and tumor characteristics, the present study also included several biases. Although three specific surgeons carried out all procedures, the surgical period was earlier for LPN than for RAPN, with the possibility of accumulated experience resulting in a higher The Japanese Urological Association

5 Parenchymal preservation in partial nephrectomy Table 3 Volumetric analysis Mean preoperative normal parenchymal volume, cc (SD) Mean postoperative normal parenchymal volume, cc (SD) Mean preservation rate of parenchymal volume, % (SD) LPN (64) RAPN (64) P < sophistication of the surgical procedure for the RAPN than the LPN group. We reported a significantly better preservation of renal functional with RAPN than LPN (95% vs 90%, P = 0.02), which is likely explained by preservation of a greater volume of renal parenchyma and shorter ischemia time with RAPN than LPN. Predictors of the preservation of renal functional in PN have been discussed in several articles. Zhang et al. analyzed the impact of parenchymal volume reduction and ischemia on subsequent renal function recovery in 83 cases of solitary kidneys managed with PN. They suggested that deleterious effects of ischemia during PN are not as profound as once believed, unless prolonged ischemia is utilized. Nephron quality before surgery and nephron quantity saved (i.e. percentage of parenchymal mass preserved) are the most important determinants of ultimate renal function after PN. 22 In addition, Zhang et al. identified an association between prolonged ischemia time and acute decline in renal function after PN, which can negatively impact subsequent functional recovery. However, most kidneys eventually recover their function, even if their function is sluggish in the first few days after surgery. In the present study, 23% of patients in the LPN group developed AKI, with a mean postoperative nadir egfr of 57 ml/min/1.73 m 2, which recovered to 60 ml/min/1.73 m 2 at 3 months and 61 ml/min/1.73 m 2 at 6 months after surgery. In contrast, 10% of patients in RAPN developed AKI, with a mean postoperative nadir egfr of 64 ml/min/1.73 m 2, which did not differ for the egfr at 3 and 6 months after surgery. From these results, a strong association between AKI development and a lower postoperative nadir egfr and a longer WIT appears likely. Although both shorter WIT and greater parenchymal preservation with RAPN than LPN might be important determinants of resulting renal functional in the present study, parenchymal preservation might have a stronger effect than WIT on long-term renal function. Although we identified a specific superiority of RAPN over LPN with regard to the preservation of renal function and parenchymal volume, Wang et al. reported additional benefits of RAPN for patients with a RENAL-NS 7, including a decrease in EBL and operative time. However, LPN was a more cost-effective approach than RAPN, providing similar perioperative, functional and oncological outcomes. 6 Although we did not compare the costeffectiveness between the two surgical outcomes, the direct cost might be higher for RAPN than LPN because of the higher cost of surgical equipment of RAPN, considering the similar length of hospital stay for both procedures. However, given that renal functional benefit is included in the cost-effectiveness, RAPN might still be considered as being superior to LPN. The present study had several limitations that should be noted. Foremost, is the retrospective nature of our study, with data collected from a single institution and a population of tertiary care patients. Second, kidney function was not evaluated by renal scintigraphy, either before or after surgery, but by the egfr as an index of global kidney function (egfr calculated from biochemical examination of blood). Furthermore, the preservation rate in global renal function was calculated relative to the contralateral kidney, which was considered to be normal in patients included in the study group; however, subtle undetected impairments in function of the normal kidney could have biased our results. Third, we cannot discount that accumulated surgeon experience might have contributed to the better outcomes of RAPN, with LPN being historically carried out in an earlier period compared with RAPN. The present study did have several strengths that warrant being noted. Foremost, we evaluated the preservation of renal parenchymal volume in a relatively large number of patients as a surgical outcome, which reflects the surgical precision of RAPN. In addition, a propensity score-matched analysis was used to adjust between-group comparisons for patient- and tumor-related characteristics. In conclusion, we report a better preservation rate of renal function and parenchymal volume with RAPN than LPN, with a similar complication rate and surgical margin status for both procedures. These results might suggest that robotic surgery is feasible, and provides more sophisticated and precise surgery in PN. Acknowledgment We acknowledge Ms Nobuko Hata for her secretarial work. Conflict of interest None declared. References 1 Weight CJ, Lieser G, Larson BT et al. Partial nephrectomy is associated with improved overall survival compared to radical nephrectomy in patients with unanticipated benign renal tumours. Eur. Urol. 2010; 58: Tan HJ, Norton EC, Ye Z, Hafez KS, Gore JL, Miller DC. Long-term survival following partial vs radical nephrectomy among older patients with early-stage kidney cancer. JAMA 2012; 307: Huang WC, Elkin EB, Levey AS, Jang TL, Russo P. Partial nephrectomy versus radical nephrectomy in patients with small renal tumors is there a difference in mortality and cardiovascular outcomes? J. Urol. 2009; 181: Ljungberg B, Cowan NC, Hanbury DC et al. EAU guidelines on renal cell carcinoma: the 2010 update. Eur. Urol. 2010; 58: Masson-Lecomte A, Bensalah K, Seringe E et al. A prospective comparison of surgical and pathological outcomes obtained after robot-assisted or pure laparoscopic partial nephrectomy in moderate to complex renal tumours: results from a French multicentre collaborative study. BJU Int. 2013; 111: Wang Y, Ma X, Huang Q et al. Comparison of robot-assisted and laparoscopic partial nephrectomy for complex renal tumours with a RENAL 2018 The Japanese Urological Association 363

6 H TACHIBANA ET AL. nephrometry score 7: peri-operative and oncological outcomes. BJU Int. 2016; 117: Wu Z, Li M, Song S et al. Propensity-score matched analysis comparing robot-assisted with laparoscopic partial nephrectomy. BJU Int. 2015; 115: Choi JE, You JH, Kim DK, Rha KH, Lee SH. Comparison of perioperative outcomes between robotic and laparoscopic partial nephrectomy: a systematic review and meta-analysis. Eur. Urol. 2015; 67: Dindo D, Demartines N, Clavien PA. Classification of surgical complications: a new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann. Surg. 2004; 240: Meeks JJ, Zhao LC, Navai N, Perry KT Jr, Nadler RB, Smith ND. Risk factors and management of urine leaks after partial nephrectomy. J. Urol. 2008; 180: Matsuo S, Imai E, Horio M et al. Revised equations for estimated GFR from serum creatinine in Japan. Am. J. Kidney Dis. 2009; 53: Kondo T, Takagi T, Morita S et al. Early unclamping might reduce the risk of renal artery pseudoaneurysm after robot-assisted laparoscopic partial nephrectomy. Int. J. Urol. 2015; 22: Gill IS, Desai MM, Kaouk JH et al. Laparoscopic partial nephrectomy for renal tumor: duplicating open surgical techniques. J. Urol. 2002; 167(2 Pt 1): Omae K, Kondo T, Takagi T et al. Renal sinus exposure as an independent factor predicting asymptomatic unruptured pseudoaneurysm formation detected in the early postoperative period after minimally invasive partial nephrectomy. Int. J. Urol. 2015; 22: Satkunasivam R, Tsai S, Syan S et al. Robotic unclamped minimal-margin partial nephrectomy: ongoing refinement of the anatomic zero-ischemia concept. Eur. Urol. 2015; 68: Shiroki R, Fukami N, Fukaya K et al. Robot-assisted partial nephrectomy: superiority over laparoscopic partial nephrectomy. Int. J. Urol. 2016; 23: Tanagho YS, Bhayani SB, Sandhu GS, Vaughn NP, Nepple KG, Figenshau RS. Renal functional and perioperative outcomes of off-clamp versus clamped robot-assisted partial nephrectomy: matched cohort study. Urology 2012; 80: Peyronnet B, Baumert H, Mathieu R et al. Early unclamping technique during robot-assisted laparoscopic partial nephrectomy can minimise warm ischaemia without increasing morbidity. BJU Int. 2014; 114: Zargar H, Akca O, Ramirez D et al. The impact of extended warm ischemia time on late renal function after robotic partial nephrectomy. J. Endourol. 2014; 29: Jang HJ, Song W, Suh YS et al. Comparison of perioperative outcomes of robotic versus laparoscopic partial nephrectomy for complex renal tumors (RENAL nephrometry score of 7 or higher). Korean J. Urol. 2014; 55: Woldu SL, Thoreson GR, Okhunov Z et al. Comparison of renal parenchymal volume preservation between partial nephrectomy, cryoablation, and radiofrequency ablation. J. Endourol. 2015; 29: Zhang Z, Zhao J, Dong W et al. Acute kidney injury after partial nephrectomy: role of parenchymal mass reduction and ischemia and impact on subsequent functional recovery. Eur. Urol. 2016; 69: Editorial Comment Editorial Comment to Robot-assisted laparoscopic partial nephrectomy versus laparoscopic partial nephrectomy: A propensity score-matched comparative analysis of surgical outcomes and preserved renal parenchymal volume Partial nephrectomy (PN) is considered a challenging procedure regardless of the kind of approach. Nevertheless, robotassisted PN, due to intrinsic advantages of the technique, is able to achieve superior renal function outcomes compared with laparoscopic PN. 1 Renal function mainly depends on the baseline quality of the kidney, on the amount of normal renal parenchyma preserved and on ischemia time. Any approach to PN should aim to avoid damage to the normal healthy kidney and reduce, limit or eliminate global renal ischemia. These goals can be reached by using tumor enucleation or minimal margin PN techniques and minimally ischemic or off-clamp PN whenever feasible. 2 In this setting, preoperative imaging with a standardized method to report tumor location and nephrometry scores is crucial for choosing the most appropriate technique. 3 In the current study, Tachibana et al. showed the superiority of robotassisted PN in terms of surgical outcomes, including renal function and the preserved renal parenchymal volume. 4 Nevertheless, surgical outcomes and volume loss are only part of all the aspects involved in renal function outcomes. To make definitive conclusions, preoperative patient features and tumor complexity should be homogenous. Hence, one of the major limitations of the study was a significant difference in terms of tumor complexity between the laparoscopic and robotic group. Currently, both surgical approaches remain viable options in the management of renal masses, but in several countries robotic surgery is limited by costs. In a similar scenario, after meticulous preoperative imaging, robot-assisted PN should be preferenced for highly complex renal tumors, in which better preservation of the factors involved in renal function outcomes is more difficult to ensure with a laparoscopic approach. Rocco Papalia M.D., Ph.D. and Riccardo Mastroianni M.D. Complex Operative Unit of Urology, Campus Bio-Medico University of Rome, Rome, Italy mpurri@yahoo.it Conflict of interest None declared. References DOI: /iju Masson-Lecomte A, Bensalah K, Seringe E et al. A prospective comparison of surgical and pathological outcomes obtained after robot-assisted or pure laparoscopic partial nephrectomy in moderate to complex renal tumours: results from a French multicentre collaborative study. BJU Int. 2013; 111: The Japanese Urological Association