Urological Science

: 2020  |  Volume : 31  |  Issue : 4  |  Page : 156--162

Comparing the predictive values of diameter-axial-polar and renal scores for long-term trifecta outcomes in robot-assisted partial nephrectomy for renal cell carcinoma

Chi Chih Lien1, Chi Hung Chiang2, Yu Chuan Lu3, Hong Chiang Chang3, Chao Yuan Huang3,  
1 Department of Urology, National Taiwan University Hospital, Taipei; Department of Surgery, Division of Urology, Camillians Saint Mary's Hospital, Luodong, Taiwan
2 Department of Urology, National Taiwan University Hospital, Taipei; Department of Urology, Medical Research and Education, Taipei Veterans General Hospital, YuanShan Branch, YiLan; Department of Nursing, Cardinal Tien Junior College of Healthcare and Management, Taipei, Taiwan
3 Department of Urology, National Taiwan University Hospital, Taipei, Taiwan

Correspondence Address:
Chao Yuan Huang
No. 7, Chung Shan S. Road (Zhongshan S. Road), Zhongzheng District, Taipei City 10002
Chi Chih Lien
No. 7, Chung Shan S. Road (Zhongshan S. Road), Zhongzheng District, Taipei City 10002


Purpose: Few studies have reported the value of the diameter-axial-polar (DAP) score in robot-assisted partial nephrectomy (RaPN) for renal cell carcinoma (RCC) and sequentially compare DAP and RENAL nephrometry score to predict long-term surgical, oncological, and functional outcomes of RaPN for renal cancer. This study demonstrated that the DAP score is effective enough to predict long-term trifecta outcomes of RaPN. Materials and Methods: We retrospectively collected clinical data of 108 patients with pathologically confirmed RCC who received RaPN by a single surgeon during 2012–2017. The patients were stratified into low, intermediate, and high complexities according to the RENAL and DAP scoring systems. We analyzed warm ischemia time (WIT), cancer-specific survival, radiographic progression-free survival, positive rate of surgical margin, renal function from the preoperative period to postoperative 1st/6th month, and postoperative complications. Results: The median follow-up period was 36 months. The 3-year cancer-specific survival rate and 3-year radiographic progression-free survival were 98.4% and 95.2%, respectively. Four patients (3.6%) had positive surgical margins. The largest decrease of renal functions from pre- to postoperative 6th month was noted in the intermediate DAP score group. No difference was observed between the DAP and RENAL scores in terms of WIT in 25 min, positive margin, complication, 3-year radiographic local recurrence, and chronic kidney disease (CKD) change, but a significant difference was observed in WIT in 20 min (area under the curve of DAP vs. RENAL = 0.81 vs. 0.54, P = 0.03). Age is an independent factor for progression to CKD after RaPN (odds ratio = 1.054, 95% confidence interval = 1.008–1.102, P = 0.022). Complications occurred in 22 patients (20.4%), and the most common postoperative complications were bleeding (12.2%), postoperative fever (0.5%), and urinary leakage (0.3%). Conclusion: The DAP score is an easy and effective tool for predicting perioperative outcomes of RaPN, especially in WIT in 20 min.

How to cite this article:
Lien CC, Chiang CH, Lu YC, Chang HC, Huang CY. Comparing the predictive values of diameter-axial-polar and renal scores for long-term trifecta outcomes in robot-assisted partial nephrectomy for renal cell carcinoma.Urol Sci 2020;31:156-162

How to cite this URL:
Lien CC, Chiang CH, Lu YC, Chang HC, Huang CY. Comparing the predictive values of diameter-axial-polar and renal scores for long-term trifecta outcomes in robot-assisted partial nephrectomy for renal cell carcinoma. Urol Sci [serial online] 2020 [cited 2020 Nov 30 ];31:156-162
Available from: https://www.e-urol-sci.com/text.asp?2020/31/4/156/290860

Full Text


The incidence of small renal mass (SRM) has increased gradually owing to modern imaging technology.[1] According to the 2017 National Comprehensive Cancer Network guidelines and the 2014 European Association of Urology guidelines, partial nephrectomy (PN) is the standard treatment for SRM.[2],[3] However, in some patients with localized renal cell carcinoma (RCC), nephron-sparing surgery (NSS) may not be suitable because of locally advanced tumor growth or because the tumor is present in an unfavorable location.[3] To standardize the description of renal tumors, objective anatomical classification systems, such as the Preoperative Aspects and Dimensions Used for an Anatomical (PADUA) classification system, the RENAL nephrometry score, and C-index, have been developed.[4],[5],[6] Such a system is helpful because it allows an objective prediction of the potential morbidity of NSS techniques.[2] Simmons et al. proposed a novel nephrometric system that integrates the optimized attributes of the RENAL and C-index systems and diameter-axial-polar (DAP) nephrometry. DAP nephrometry involves a simplified methodology, decreased measurement variability, and a much stronger correlation with clinical outcomes.[7] However, some comparisons of DAP and RENAL scores for warm ischemia time (WIT), margin, and complications have been published,[8] but no head-to-head comparisons of survival or recurrence have yet been conducted. In this study, we examined correlations between DAP and RENAL scores and long-term outcomes. Finally, we compared the abilities of DAP and RENAL scores to predict trifecta (oncological, functional, and surgical) outcomes.

 Subjects and Methods

This study is registered with the National Taiwan University Hospital Research Ethics Committee (number 201305059RINC). We retrospectively evaluated consecutive patients undergoing RaPN approaches for localized renal tumors between January 2012 and December 2017 by a single surgeon, Prof. Chao-Yuan Huang, in the National Taiwan University Hospital. The choice of used/applied surgical approach was based on the cost, expertise of the surgeon, and patient preference. We excluded patients with multiple and bilateral renal tumors, solitary kidney, or pathology not comparable with RCC. All these patients had received magnetic resonance imaging or computed tomography before PN, per 3 months after surgery until 1 year, then biannually for 3 years, and then annually until the 5th year.

We recorded patients' demographics (age, gender, and body mass index), perioperative outcomes (console time, estimated blood loss [EBL], WIT, perioperative complications [classified by the Clavien–Dindo system], and length of hospitalization), and pathological features. We pursued trifecta outcomes in our study, namely surgical, functional, and oncological outcomes. Surgical outcomes are defined as complications, margin status, and WIT. Functional outcomes are defined as the deterioration of renal function. Oncological outcomes are defined as cancer-specific survival and radiographic progression-free survival. Renal function was assessed using the Modification of Diet in Renal Disease (MDRD) equation for determining the estimated glomerular filtration rate (eGFR) on the day before the operation in the postoperative 1st month and in the postoperative 6th month. Changes in renal functions were recorded as the deterioration of the chronic kidney disease (CKD) stage and percentage changes in eGFR.

The width of parenchymal ischemia and resection was reported by the surgeon. RENAL and DAP scores were calculated according to previously reported protocols.[5],[7] The RENAL score is based on five components: R, radius; E, exophytic/endophytic; N, nearness; A, anterior/posterior; and L, location. The DAP score is based on three components: D, diameter; A, axial; and P, polar. The DAP components are scored as follows:

(D) diameter: score1, <2.4 cm; score 2, 2.4–4.4 cm; scores 3, >4.4 cm(A) distance from the center of the kidney axis to the closest tumor edge: score 1, >1.5 cm; score 2, ≤1.5 cm; and score 3, tumor touching or overlapping the center of the kidney(P) distance from the kidney equatorial plane to the tumor edge: score 1, >2 cm; score 2, ≤2 cm; and score 3, tumor visible on the middle plane.

Based on total RENAL scores, the patients were divided into three groups: low risk, 4–6; intermediate risk, 7–9; and high risk, 10–12. Based on total DAP scores, the patients were divided into three groups: low risk, 3–4; intermediate risk, 5–6; and high risk, 7–9. Continuous variables are represented as mean ± standard deviation, and ordinal variables are represented as median (interquartile range). Spearman correlation analysis was used to evaluate the relationship between DAP and RENAL scores as well as perioperative outcomes. Results of uni- and multivariate analyses of various clinical variables and changes in renal functions were evaluated using linear regression analysis. The predictability of DAP and RENAL scores for renal function was compared using receiver operating characteristic curve analysis. All analyses were performed using SPSS version 22 (SPSS, Chicago, IL, USA) with P < 0.05 considered to be statistically significant.


During the study period, 182 patients received RaPN. A total of 73 patients were excluded because of incomplete data or because they were not available or follow-up. In addition, one patient was excluded because the pathological examination showed a sarcomatoid component. Finally, 108 patients were enrolled in this study for the final analysis. The clinical and pathological characteristics of the 108 patients in this study are shown in [Table 1]. RENAL and DAP distributions and individual components are shown in [Table 2]. The relationships between RENAL and DAP scores and trifecta outcomes are also presented in [Table 2].{Table 1}{Table 2}

The median follow-up was 36 months. The 3-year cancer-specific survival rate for all patients was 98.4%. The 3-year radiographic progression-free survival rate was 95.2%.

Significant differences in operative time, console time, WIT, and EBL were observed among the three risk groups for RENAL (P < 0.001, <0.001, 0.003, and 0.024, respectively, Kruskal–Wallis test) and DAP (P < 0.001, <0.001, 0.001, and <0.001, respectively, Kruskal–Wallis test) scores [Table 3]. WIT in the low-risk group according to the RENAL score was significantly shorter than that in the intermediate- and high-risk groups (P = 0.03 and 0.01, respectively, Mann–Whitney U-test with Bonferroni correction). No significant difference in WIT was observed between the low- and intermediate-risk groups for the DAP score (P = 0.10, Mann–Whitney U-test), but WIT was significantly lower in the low-risk group than in the high-risk group (P = 0.02, Mann–Whitney U-test). EBL in the high-risk group for the DAP score was significantly higher than that in the low- and intermediate-risk groups (P < 0.001, Mann–Whitney U-test).{Table 3}

The largest decrease of renal function from the preoperative period to postoperative 6th month was noted in the intermediate-risk group for the DAP score. In our study, the predictive value of long-term outcomes of the DAP score was not inferior to that of the RENAL score, including prediction for WIT in 25 min [area under the curve [AUC] of DAP vs. RENAL = 0.61 vs. 0.51, P = 0.34, [Figure 1], prediction for a positive margin [AUC of DAP vs. RENAL = 0.50 vs. 0.55, P = 0.08, [Figure 2], prediction for the 3-year radiographic local recurrence [AUC of DAP vs. RENAL = 0.55 vs. 0.55, P = 0.08, [Figure 3], prediction for complication [AUC of DAP vs. RENAL = 0.58 vs. 0.55, P = 0.06, [Figure 4], and prediction for the change in CKD status [AUC of DAP vs. RENAL = 0.54 vs. 0.48, P = 0.10, [Figure 5], but the prediction of WIT in 20 min was AUC of DAP vs. RENAL = 0.81 vs. 0.54, P = 0.03, [Figure 6]. Our study also demonstrated that age is an independent factor for the progression to CKD after RaPN [odds ratio = 1.054, 95% confidence interval [CI] = 1.008–1.102, P = 0.022, [Table 4]. Complications occurred in 22 patients (20.4%), and the most common postoperative complications were bleeding (12.2%), postoperative fever (0.5%), and urinary leakage (0.3%). No severe (≥ Grade 3) complications were noted in our cohort.{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Figure 6}{Table 4}


In the European Organization for Research and Treatment of Cancer trial 30904, PN decreased the incidence of at least moderate renal dysfunction (eGFR <60 mL/min/1.73 m 2).[9] In some studies, PN has even contributed to better overall survival by reducing the incidence of sequelae of CKD and cardiovascular morbidity, which is compared to radical nephrectomy.[10] Therefore, nephrometry scores have become increasingly more important for the pre-NSS evaluation of SRM after 2009, not only as an aid for urological surgeons facing renal masses with borderline complexity but also as a standard reporting system for outcome comparisons.[4],[5] The first RaPN was reported in 2004,[11] and it was proven that RaPN is a safe and feasible technology for PN. Hung et al. also reported “trifecta” (surgical, oncological, and functional) outcomes as a gold standard in recent eras for PN.[12] However, current studies lack data regarding nephrometry scores that best predict the trifecta outcomes of RaPN in the Asian population, and our study provides the first trifecta outcome in RaPN based on the Taiwanese population.

The median WIT (34 min) was longer than the other PN series (mean: 19.2 min).[13] It may be caused by a larger tumor size or the conventional clamping technique used in our cohort.[12] In detail, before hilar occlusion, mannitol 12.5 g is given intravenously to aid renal protection by facilitating osmotic diuresis. Hilar clamping is performed using laparoscopic bulldog clamps. If bulldog clamps are used, the renal artery is clamped only in most of the cases. The hilum is occluded and the tumor is resected along the previously scored margin using cold scissors. Renorrhaphy is performed in two layers using one robotic needle driver. A 15 cm V-LOC suture (Medtronic Parkway, Minneapolis, MN, USA) with a knot and Hem-o-Lok clip (Teleflex Medical, Kenosha, WI, USA) was applied to the free end and used as a running suture of the tumor excision bed. Then, the laparoscopic bulldog clamp is unclamped and another mannitol 12.5 g is given intravenously. Godoy et al. found that WIT of 40 min appears to be an appropriate cutoff time for predicting postoperative renal impairment.[14] Furthermore, Thompson et al.[15] revealed 5% and 6% increases in the risk of acute renal failure and new-onset stage 4 CKD, respectively, for each 1 min increase in WIT and an optimal WIT cutoff of 25 min to help prevent renal function decline.[15] Therefore, we tested the predictive values of RENAL and DAP scores, respectively, for WIT in 20 and 25 min, which may be meaningful in long-term renal function follow-up. Moreover, our cohort demonstrates that the DAP score is superior to the RENAL score in predicting WIT in 20 min [Figure 6].

Although the definition of the safest width of a healthy renal margin to achieve oncological efficacy and the safest resection technique during PN continues to be widely debated, the resection technique in our cohort was a conventional standard resection. Minervini et al. presented a meta-analysis demonstrating that simple enucleation is not inferior to the standard method in terms of a positive surgical margin and local-regional recurrence in patients undergoing PN.[16] Only four patients (3.6%) had a positive surgical margin, and their DAP scores were 8, 4, 7, and 7. Hennessey et al. presented 3.2% of positive surgical margins in RaPN for complex renal lesions,[17] and our result is the same as that of Hennessey et al. The patient with four DAP scores exhibited the final pathology of a carcinoid tumor. Our study reports an equally powerful predictive value of the DAP score than that of the RENAL score for positive surgical margins [AUC of DAP vs. RENAL = 0.50 vs. 0.55, P = 0.08, [Figure 2]. The DAP score can improve the shortcomings of the relatively strict cutoff of a 7 cm distance and lax cutoff of a 4 cm distance in the RENAL score.[7] The result offers physicians useful information regarding a higher risk of local recurrence in the high-risk group for the DAP score, although the relationship between local recurrence and the positive surgical margin is still under debate.[18] The median time to local recurrence was 17 months (range: 3–18), which was shorter than that of the other series (23 months [range: 2–107]).[18]

In the largest single-center series to date, which consisted of 400 patients undergoing RaPN, a total of 11 cases (2.7%) of intraoperative complications and 61 cases (15.3%) of postoperative complications were reported, which were mainly low grade (Grades 3 and 4 in 3.2%).[13] A similar intraoperative complication rate was reported for our study. Blood loss of >500 mL was the only intraoperative complication (12 cases, 11.1%). A total of 10 cases (9.2%) of postoperative complications (neither Grade 3 nor Grade 4 complications) were noted. Therefore, neither the RENAL and DAP scores could predict the complication rate in our study. Compared with other studies, which showed that the nephrometry score can predict severe complication rates,[17],[19] our results may be due to selection bias or the nature of our database from a single experienced surgeon.[20]

Many studies have confirmed the benefits of PN in terms of improved renal function and overall survival.[9],[21],[22],[23] The basis of these improved outcomes is the preservation of functional nephron mass. Despite the obvious importance of this factor, it has not been extensively studied because of the challenges posed by the measurement of the functional volume change. Our study demonstrated that both the DAP and RENAL scores failed to predict the change in CKD status [AUC of DAP vs. RENAL = 0.54 vs. 0.48, P = 0.10, [Figure 5]. Wang et al. presented a different result for the DAP score as an independent factor for renal function reduction.[24] One explanation for our result is that the DAP and RENAL scores include not only the tumor size but also its position. Another reason for this insignificant result may be the relatively short follow-up period. However, our result demonstrated that age is an independent factor for progression to CKD after RaPN (odds ratio = 1.054, 95% CI = 1.008–1.102, P = 0.022). Thus, younger patients may have more benefit in renal function preservation than older patients, even for borderline complicated renal mass.

A comparison of RENAL, PADUA, C-index, and DAP scores from Germany indicated that the RENAL score correlates best with margin, ischemia, and complication (negative margin, ischemia time <20 min, and no Grade 3 or more severe complication) achievement in NSS. However, only 17 patients (9%) received RaPN. In addition, in the subgroup analysis of RaPN, no complication occurred in all the 17 patients that received RaPN, which is the same as that in our study.[8] No comparison of the four nephrometry scores above in the RaPN subgroup was made because of the relatively small sample size.

Although we chose the single-surgeon database to avoid intersurgeon bias, some limitations still existed in our cohort. First, the study was retrospective with a small number of cases and may need a more long-term follow-up period. Second, the mean tumor size (3.5 cm) was greater than that in other series of PN (mean 2.9 cm). Third, we assessed eGFR using the MDRD equation. For a more accurate estimation of renal function, renal scintigraphy should be used. Fourth, we considered ischemia time as a binary variable, which may have resulted in an interpretation error. We considered that every minute of cold ischemia time and WIT does not have the same weight in regression analysis.


The DAP score is an easy and effective tool for predicting perioperative outcomes of RaPN, especially in WIT in 20 min.

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Conflicts of interest

There are no conflicts of interest.


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