
==== Front
Int J Surg
Int J Surg
JS9
International Journal of Surgery (London, England)
1743-9191
1743-9159
Lippincott Williams & Wilkins Hagerstown, MD

39171960
IJS-D-24-01422
10.1097/JS9.0000000000001774
00006
3
Original Research
Clinical features and surgical strategy of retroperitoneal liposarcoma involving the kidney capsule: a retrospective comparative cohort study
Li Yiyuan MD 17761230235@163.com

Zhao Jichun MD zjcwch@163.com

Huang Bin MD hbwchscu@163.com

Guo Qiang MD *rosebud-1@163.com

Department of General Surgery, Division of Vascular Surgery, West China Hospital, Sichuan University, Chengdu, Sichuan Province, People’s Republic of China
* Corresponding author. Address: Department of General Surgery, Division of Vascular Surgery, West China Hospital, Sichuan University, Chengdu 610041, Sichuan Province, People’s Republic of China. Tel.: +86 288 542 2605. E-mail: rosebud-1@163.com (Q. Guo).
9 2024
13 6 2024
110 9 53555362
11 4 2024
29 5 2024
Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc.
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial License 4.0 (CCBY-NC), where it is permissible to download, share, remix, transform, and buildup the work provided it is properly cited. The work cannot be used commercially without permission from the journal. http://creativecommons.org/licenses/by-nc/4.0/

Background:

Valid and generalizable data on the clinical features and surgical strategies for retroperitoneal liposarcoma (LPS) involving the kidney capsule remain scarce. This study aimed to investigate the clinical characteristics, morbidity, mortality, and long-term survival of patients with retroperitoneal LPS involving the kidney capsule.

Methods:

The authors analyzed a prospectively maintained database of patients who underwent surgical resection for retroperitoneal LPS between 2015 and 2020. The patients were categorized into kidney capsule or no kidney capsule groups based on the presence or absence of kidney capsule involvement. A kidney-sparing strategy for retroperitoneal LPS involving the kidney capsule was developed. The primary outcome measure was overall survival (OS). The cumulative event probability curve was estimated using the Kaplan–Meier, and differences between groups using the Log-Rank.

Results:

The study population consisted of 128 patients—54 with and 74 without kidney capsule involvement. Of these patients, 70 were female (54.7%) and 58 were male (45.3%), with a median age of 55. The median follow-up duration was 35 months. Postoperative morbidity, mortality, length of hospital stay, length of ICU stay, OS, and recurrence-free survival (RFS) did not differ significantly between the groups. Eleven patients developed postoperative acute kidney injury (AKI), and one patient required dialysis during the follow-up period. In multivariable logistic regression analysis, only nephrectomy was independently associated with postoperative AKI. Subgroup analysis of patients with kidney capsule involvement showed that nephrectomy did not improve OS or RFS but significantly decreased postoperative estimated glomerular filtration rate.

Conclusion:

Nephrectomy was associated with an increased risk of postoperative AKI after retroperitoneal LPS resection. A kidney-sparing strategy for retroperitoneal LPS involving the kidney capsule achieved optimal clinical outcomes.

Keywords:

kidney capsule
overall survival
renal function
retroperitoneal liposarcoma
OPEN-ACCESSTRUE
SDCT
==== Body
pmcIntroduction

Highlights

The clinical features and surgical outcomes of retroperitoneal liposarcoma (LPS) involving the kidney capsule remain unclear.

Nephrectomy is associated with an increased risk of postoperative acute kidney injury following retroperitoneal LPS resection.

A kidney-sparing strategy for retroperitoneal LPS involving the kidney capsule was associated with optimal clinical outcomes.

Complete en bloc gross resection is the cornerstone in managing retroperitoneal sarcomas (RPSs), but ongoing debate persists regarding the optimal extent of surgery for these tumors1,2. To improve locoregional tumor control, compartmental resection often requires multivisceral resection of contiguously involved organs, which might increase morbidity and mortality associated with these extended resections3,4. The kidney is one of the most frequently resected organs in en bloc resection for RPSs5. However, there is debate regarding the low frequency of direct invasion of the kidney by tumor, even when the tumor encases the kidney6. Additionally, nephrectomy is associated with an increased risk of postoperative acute kidney injury (AKI) following RPS resection7. Thus, it is critical to balance optimal short-term and survival outcomes with the risk of subsequent renal impairment before the decision of en bloc resection with concomitant nephrectomy is made.

Anatomically, the kidney capsule is one of the possible sites of liposarcoma (LPS), which might explain why retroperitoneal LPS has a higher frequency of nephrectomies than other histologic types8,9. Nevertheless, the origin of LPS has not been discussed because determining the origin of the primary tumor site seems challenging. As it is feasible to identify whether the kidney capsule is involved, we hypothesized that patients with retroperitoneal LPS involving the kidney capsule has different clinical features and surgical outcomes with those without kidney capsule involvement. We also explored surgical strategies for patients with retroperitoneal LPS involving the kidney capsules. Thus, the primary aim of this study was to investigate the clinical characteristics, short-term outcomes, and long-term survival of patients with retroperitoneal LPS involving the kidney capsule. In addition, we attempted to determine the incidence of AKI, identify the preoperative and perioperative factors associated with postoperative AKI, and evaluate the relative clinical benefits and disadvantages of en bloc nephrectomy for patients with retroperitoneal LPS involving the kidney capsule.

Methods

Patient population

All consecutive patients without any sex/age restriction who underwent surgery for histologically confirmed primary/recurrent RPS between 2015 and 2020 were identified from a prospectively maintained institutional database at West China Hospital, Sichuan University. As this was a retrospective cohort study with anonymized data, the requirement for informed consent was waived. Patients with LPS according to the Transatlantic Australasian RPS working group diagnostic criteria who underwent curative intent surgery were included in this study10. The exclusion criteria included insufficient clinical or histopathological data, histological subtypes other than LPS, and tumor-unrelated or emergency surgery. Clinicopathological data were extracted, and missing data were retrospectively collected from the patients’ electronic medical records. This study was approved by the Institutional Review Board of the West China Hospital of Sichuan University. The study was registered in the Chinese Clinical Trials Registry (ChiCTR) as ChiCTR 2300076349 (http://www.chictr.org.cn/enindex.aspx). The report of this study was written following the guidelines outlined in the strengthening the reporting of cohort, cross-sectional, and case–control studies in surgery (STROCSS) statement11 (Supplemental Digital Content 1, http://links.lww.com/JS9/C747).

Variable definitions and study design

Clinicopathological factors included in the analyses were age, sex, BMI, comorbidities, recurrence status, adjuvant treatment, margin status, organ resection, transfusion, renal function stage, histological subtype, and tumor grade. The histological subtypes were grouped into well-differentiated LPS, dedifferentiated LPS, and others. Histological grade was defined according to the Federation Nationale des Centres de Lutte Contre le Cancer (FNCLCC) grading system as either low-risk (G1), intermediate-risk (G2), or high-risk (G3)12. AKI was defined as an increase in serum creatinine to 1.5 times or more of baseline within 7 days after surgery13. The stages of chronic kidney disease (CKD) were defined according to the definition of the National Kidney Foundation14. Surgical resections were classified as macroscopically complete (R0/R1) or incomplete (R2). Kidney capsule involvement was defined as the absence of a rim of normal tissue at the surface of the kidney capsule, with confirmed histological invasion or infiltration into the kidney capsule. A kidney-sparing strategy for retroperitoneal LPS involving the kidney capsule was developed. Nephrectomy was performed when the kidney was directly invaded by the tumor or renal hilum or when more than half of the kidney was encased by the tumor. The operating surgeon determined the need for vascular/organ resection at the time of surgery. All the surgical procedures were performed by two surgical teams in a single center. Radiation, chemotherapy, or both were administered as neoadjuvant or adjuvant therapies to a selected group of patients after a multidisciplinary discussion. All patients were followed-up every 3 months for the first year and then every 6 months through clinical evaluation and contrast-enhanced computed tomography of the abdomen every 6–12 months after surgery.

Outcome measures

The patients were divided according to the presence of kidney capsule involvement (kidney capsule and no-kidney capsule groups). The primary endpoint was long-term overall survival (OS). Second, short-term morbidity and mortality, length of hospital stay, length of ICU stay, postoperative AKI, and recurrence-free survival (RFS) were compared. Subgroup analyses were conducted for patients who underwent nephrectomy and those with primary or recurrent RPS. OS was defined as the time from the date of primary tumor diagnosis to the time of death or last contact. RFS was defined as the time from the date of primary tumor diagnosis to the time of disease recurrence, death, or last contact. Morbidity and mortality data abstraction was performed for a 30-day postoperative period and categorized according to the Clavien–Dindo classification15. Major complications were defined as any Clavien–Dindo grade ≥3 complication.

Statistical analysis

Mean values with SD were reported for normally distributed continuous variables. In cases where continuous variables were not normally distributed, median values with interquartile ranges (IQR) were reported. Binary and categorical variables are reported as proportions. Categorical and continuous variables were analyzed using the χ 2 test, Fisher’s exact test, and Student’s t-test. For nonparametric data, the Mann–Whitney U test was applied. To determine the independent predictors of postoperative AKI, a two-level hierarchical mixed effects multivariate logistic regression analysis was conducted. OS and RFS were estimated using the Kaplan–Meier approach and compared between the groups using a log-rank test. A two-tailed P<0.05 and 95% CI around the odds ratio (OR) that did not cross one were considered statistically significant. Statistical analyses were performed using SPSS software (version 26.0; SPSS, Inc.).

Results

Patient characteristics

The study cohort included 292 patients who underwent surgery for RPS during the study period. Figure 1 shows a flowchart of the patient selection process. We excluded 40 patients owing to the following reasons: patients who underwent tumor-unrelated or emergency surgery (n=11), patients diagnosed with incomplete data records (n=13), and those lost to follow-up (n=13). Patients whose pathological diagnoses were not LPSs were also excluded from the analysis (n=124). The final study population comprised 128 patients. Of these, 54 patients (38.9%) exhibited kidney capsule involvement, while 74 (61.1%) did not. The characteristics and demographics of the patients, along with the clinical variables in both the kidney capsule and nonkidney capsule groups, are summarized in Table 1. The pathological characteristics and FNCLCC grades were similar between the kidney capsule and no-kidney capsule groups. However, patients in the kidney capsule group had a larger tumor size (75.9 vs. 54.1% tumor size ≥20 cm, P=0.030) and higher contiguous organ resection rate (63.0 vs. 36.5%, P=0.003).

Figure 1 Flowchart of included patients.

Table 1 Baseline demographic and clinical characteristics of the study population.

Characteristic	Kidney capsule (n=54)	No kidney capsule (n=74)	P	
Sex (female/male)	31/23	39/35	0.208	
Age, median (IQR)	56 (47–62)	54 (45–62)	0.374	
Comorbidity	
 Hypertension	5	8	0.744	
 Diabetes	3	5	0.782	
 Ischemic heart disease	1	1	0.822	
 Cerebrovascular disease	0	1	0.391	
Recurrent tumor resection	21	39	0.122	
Tumor size			0.030	
 <20 cm	13	34		
 ≥20 cm	41	40		
Pathology			0.254	
 Well-differentiated LPS	24	26		
 Dedifferentiated LPS	28	40		
 Others	2	8		
FNCLCC grade			0.507	
 Low	9	12		
 Moderate	28	27		
 High	17	35		
Neoadjuvant radiation	2	6	0.309	
Neoadjuvant chemotherapy	3	10	0.141	
Postoperative radiotherapy	1	4	0.305	
Postoperative chemotherapy	3	5	0.782	
Margin status			0.167	
 R0/1	48	59		
 R2	6	15		
Contiguous organ resection	34	27	0.003	
Preoperative CKD stage			0.155	
 G1	36	42		
 G2	12	26		
 G3	6	3		
 G4	0	2		
 G5	0	1		
Transfusion	30	40	0.866	
Postoperative AKI	9	2	0.005	
30 days mortality	0	3	0.182	
Complication	5	5	0.602	
Postoperative VTE	6	6	0.565	
Length of stay (mean, days)	17.7±10.3	19.6±13.9	0.178	
Length of ICU stay (mean, days)	2.5±1.4	2.3±1.1	0.331	
AKI, acute kidney injury; CKD, chronic kidney disease; FNCLCC, Federation Nationale des Centres de Lutte Contre le Cancer; IQR, interquartile range; LPS, liposarcoma; VTE, venous thromboembolism.

Short-term outcomes

Table 1 summarizes the postoperative outcomes in each group. No significant differences were observed between the kidney capsule and no-kidney capsule groups in 30-day mortality (0 vs. 4.1%), major complications (11.4 vs. 6.5%), length of stay (17.7±10.3 days vs. 19.6±13.9 days), and length of ICU stay (2.5±1.4 days vs. 2.3±1.1 days). Patients in the kidney capsule group yielded a significantly higher rate of postoperative AKI (16.7 vs. 2.7%, P<0.001). In the kidney capsule group, 30-day mortality, major complications, length of stay, and length of ICU stay were comparable after en bloc nephrectomy and kidney-sparing excision (See Supplementary Table S1, Supplemental digital content 2, http://links.lww.com/JS9/C748).

Impact of nephrectomy on postoperative renal function

A total of 35 (27.3%) patients underwent concomitant nephrectomy, and the remaining 93 (62.7%) were assigned to the no-nephrectomy group. Two patients in the no-kidney capsule group underwent concomitant nephrectomy because of long-segment ureteral involvement. Patients in the nephrectomy group had a larger tumor size and a higher transfusion rate (74.3 vs. 36.6%) (See Supplementary Table S2, Supplemental digital content 2, http://links.lww.com/JS9/C748). The baseline prevalence rates of CKD were 14.3 and 7.5% in the nephrectomy and no-nephrectomy groups, respectively. Eleven patients developed postoperative AKI. Patients who underwent nephrectomy had a higher rate of postoperative AKI than those who did not (22.9 vs. 3.2%, P<0.001). None of the patients required postoperative dialysis during their hospital stay; however, one patient who underwent nephrectomy required dialysis during the follow-up period.

Table 2 lists the potential parameters that could be used to predict postoperative AKI. Sex, age, BMI, histological subtype, FNCLCC grade, recurrence, concomitant organ resection, preoperative CKD stage, primary tumor site, nephrectomy, and transfusion were included in a multivariate analysis to predict postoperative AKI. On multivariable logistic regression, only nephrectomy was independently associated with postoperative AKI (OR=1.637, 95% CI: 1.161–2.289, P=0.009).

Table 2 Multivariate analysis of risk factors for postoperative acute kidney injury.

Variables	Odds ratio	95% CI	P	
Sex	0.493	0.072–3.393	0.472	
Age	1.676	0.466–6.025	0.429	
BMI	1.279	0.676–2.318	0.329	
Histological subtype	0.677	0.145–3.156	0.620	
FNCLCC grade	1.013	0.280–3.669	0.984	
Recurrence	1.064	0.226–5.002	0.937	
Concomitant organ resection	1.076	0.398–2.913	0.885	
Preoperative CKD stage	0.246	0.044–1.383	0.111	
Kidney capsule involvement	1.757	0.151–20.403	0.652	
Nephrectomy	1.637	1.161–2.289	0.009	
Transfusion	3.441	0.783–15.123	0.102	
CKD, chronic kidney disease; FNCLCC, Federation Nationale des Centres de Lutte Contre le Cancer.

Median preoperative and postoperative values of estimated glomerular filtration rate (eGFR) in the no-nephrectomy groups were 95.08 (81.30–107.16) and 101.62 (83.67–108.75) ml/min/1.73 m2, respectively (Fig. 2). Median preoperative and postoperative values of eGFR in the nephrectomy groups were 94.16 (66.55–111.57) and 78.04 (56.46–100.10) ml/min/1.73 m2, respectively. As shown in Table 3, postoperative measurements of eGFR increased significantly compared with preoperative values of eGFR in the no-nephrectomy group (HR 11.12, 95% CI: 2.96–19.28, P=0.009). However, in the nephrectomy group, postoperative eGFR decreased remarkably (HR –5.00, 95% CI: –1.95 to –8.06, P=0.002). Subgroup analyses of patients with kidney capsule involvement revealed that postoperative eGFR significantly decreased in the nephrectomy group (HR –12.34, 95% CI: –20.43 to –4.25, P=0.004), and postoperative eGFR of the patients with primary retroperitoneal LPS in no-nephrectomy group increased significantly (HR 8.81, 95% CI: 3.19–14.42, P=0.004).

Figure 2 Median preoperative and postoperative estimated glomerular filtration rates (eGFR).

Table 3 Preoperative and postoperative differences of eGFR.

		eGFR (ml/min/1.73 m2)	
	N	HR	95% CI	P	
Entire cohort	
 Nephrectomy	35	–5.00	–1.95 to –8.06	0.002	
 No nephrectomy	93	11.12	2.96–19.28	0.009	
Kidney capsule involvement	
 Nephrectomy	33	–12.34	–4.25 to –20.43	0.004	
 No Nephrectomy	21	4.49	–1.09 to 10.07	0.106	
Primary LPS	
 Nephrectomy	19	–4.93	–13.39 to 3.54	0.241	
 No Nephrectomy	49	8.81	3.19–14.42	0.004	
Recurrent LPS	
 Nephrectomy	16	–8.08	–20.71 to 4.55	0.189	
 No Nephrectomy	44	1.55	–2.73 to 5.83	0.466	
eGFR, estimated glomerular filtration rates, HR, hazards ratio; LPS, liposarcoma.

Survival analyses

The median follow-up duration was 35 months (IQR, 23–48). The 5-year OS rates of the patients in the kidney capsule and no-kidney capsule groups were 34 and 28%, respectively. The estimated median OS did not differ between the kidney capsule and no-kidney capsule (45.5 months, 95% CI: 36.7–54.3 vs. 45.4 months, 95% CI: 38.5–52.3; P=0.966; Fig. 3A) groups. Additionally, kidney capsule involvement did not affect RFS (kidney capsule vs. no kidney capsule: HR, 0.677; 95% CI: 0.314–1.289; P=0.463).

Figure 3 Kaplan–Meier graph for overall survival of patients in (A) kidney capsule/no kidney capsule group in the entire cohort and (B) nephrectomy/no nephrectomy group in the subgroup analyses cohort (patients with vascular involvement).

The subgroup analysis of patients with kidney capsule involvement showed that the 5-year OS rates of patients in the nephrectomy and no-nephrectomy groups were 33 and 33%, respectively. Figure 3B depicts the Kaplan–Meier estimates of OS. No significant difference was observed in the estimated median OS (nephrectomy vs. no-nephrectomy: 44.1 months, 95% CI: 33.1–55.1 vs. 43.6 months, 95% CI: 34.7–52.4; P=0.262) or DFS (nephrectomy vs. n- nephrectomy: 28.0 months, 95% CI: 26.1–29.9 vs. 20.0 months, 95% CI: 15.1–24.9; P=0.460).

Of the entire cohort, 68 patients (53.1%) underwent primary resection, and the remaining 60 patients (46.9%) had recurrent retroperitoneal LPS. Subgroup analyses of patients with primary or recurrent retroperitoneal LPS did not reveal differences in OS or RFS between the nephrectomy and no-nephrectomy groups (Table 4).

Table 4 Overall survival and disease-free survival for different cohorts.

	Median OS, mo	HR (95% CI) for OS	HR (95% CI) for DFS	
Entire cohort		1.031 (0.917–1.281), P=0.966	0.677 (0.314–1.289), P=0.463	
 Kidney capsule involvement	45.5 (36.7–54.3)			
 No kidney capsule involvement	45.4 (38.5–52.3)			
Entire cohort		0.826 (0.413–1.671), P=0.550	0.991 (0.977–1.012), P=0.995	
 Nephrectomy	44.3 (33.6–55.0)			
 No nephrectomy	46.0 (39.8–52.2)			
Kidney capsule involvement		1.084 (0.718–1.687), P=0.262	1.515 (0.863–2.679), P=0.460	
 Nephrectomy	44.1 (33.1–55.1)			
 No Nephrectomy	43.6 (34.7–52.4)			
Primary LPS		1.094 (0.814–1.251), P=0.781	1.103 (0.637–1.912), P=0.669	
 Nephrectomy	49.8 (37.4–62.3)			
 No Nephrectomy	49.5 (40.1–58.9)			
Recurrent LPS		0.650 (0.314–1.344), P=0.129	0.769 (0.353–1.675), P=0.443	
 Nephrectomy	33.1 (19.0–47.2)			
 No Nephrectomy	41.8 (34.4–49.1)			
DFS, disease-free survival; HR, hazards ratio; LPS, liposarcoma; OS, overall survival.

Discussion

This study investigated long-term survival, postoperative morbidity, and mortality in patients with or without kidney capsule involvement in retroperitoneal LPS. The results showed that the OS and RFS rates of patients with retroperitoneal LPS with or without kidney capsule involvement did not differ significantly. In addition, postoperative morbidity and mortality rates did not differ between the two groups. Furthermore, the patients who underwent nephrectomy had a higher rate of postoperative AKI. Although not in line with our hypothesis, the results of subgroup analyses contribute to clinical decision-making by showing that nephrectomy did not improve long-term survival but increased the rate of postoperative AKI in patients with retroperitoneal LPS with kidney capsule involvement.

Given the high heterogeneity of the long-term outcomes of different histologic subtypes and LPS being the predominant subtype requiring en bloc resection with nephrectomy, we only enrolled patients with LPS in this study. Previous studies on retroperitoneal LPS have rarely discussed the origin of the primary tumor. Terakawa et al.16 reported a case of retroperitoneal LPS arising from the renal capsule. They determined the origin of the primary tumor using angiography, which demonstrated a large perirenal tumor fed from the renal capsular artery. However, retroperitoneal LPS originating from the ipsilateral retroperitoneal fat involving the kidney capsule may also be fed from the renal capsular artery. Consequently, in this study, we divided the patients into two groups according to the presence of kidney capsule involvement and defined kidney capsule involvement as the absence of a rim of normal tissue at the tumor-to-kidney interface with confirmed histological invasion or infiltration into the kidney capsule.

Intraoperative macroscopic assessment of appropriate resection margins in retroperitoneal LPS remains challenging, particularly for well-differentiated LPS, where distinguishing tumor tissue from normal fat is difficult17. Given the uncertainty regarding margin definition, the updated trans-Atlantic Australasian RPS working group consensus on managing primary RPS in adults recommended that an extended approach to systematically resect adherent viscera, irrespective of expected microscopic infiltration, should be considered for retroperitoneal LPS10. They advocate for a policy of resecting only structures/viscera visibly invaded by LPS, as it reduces the likelihood of leaving residual disease being in the operative bed. They suggest that clearing all ipsilateral retroperitoneal fat can achieve the goal of removing tissue at risk of involvement by LPS. However, these recommendations were made based on expert opinions without any relevant study. Gaston et al.18 described a case of nephron-sparing resection of a giant perirenal LPS involving a solitary kidney. Excision of this mass with the renal capsule allowed the patient to be margin negative and maintain normal renal function. Thus, evidence regarding the appropriate surgical extent of retroperitoneal LPS involving the kidney capsules remains scarce. To our knowledge, this is the first large cohort study to investigate the clinical characteristics, short-term outcomes, and long-term survival of patients with retroperitoneal LPS involving the kidney capsule.

Limited studies have evaluated the impact of nephrectomy on postoperative renal function in patients with RPSs5,6,19,20. All of these studies have reported that nephrectomy is associated with an increased risk of postoperative AKI and ARF following RPS resection. However, none of these studies have described the criteria for nephrectomy. The baseline characteristics, especially the histologic subtype proportions, were significantly different between the nephrectomy and no-nephrectomy groups5,6. As the frequency of kidney capsule involvement in retroperitoneal LPS is high, it is important to assess the relative clinical benefit and risk of en bloc nephrectomy for retroperitoneal LPS involving the kidney capsule; additionally, determining the optimal surgical extent for varying degrees of kidney capsule involvement is crucial. Our study differs from these studies by not only investigating the impact of nephrectomy on postoperative renal function but also seeking to discover the optimal surgical strategy for retroperitoneal LPS involving the kidney capsule. Interestingly, we found that postoperative eGFR increased significantly compared to preoperative values of eGFR in the no-nephrectomy group, and conversely, postoperative eGFR decreased remarkably in the nephrectomy group. A possible explanation for this is that ureteral compression caused by the large mass was relieved postoperatively in the no-nephrectomy group. In addition, consistent with a previous trial, nephrectomy was independently associated with postoperative AKI in the multivariable logistic regression analysis.

We hypothesized that retroperitoneal LPSs involving the kidney capsule have different clinical features and surgical outcomes from those without kidney capsule involvement. Although more contiguous organ resections were performed in the kidney capsule group and a larger tumor size was observed, the pathological characteristics, FNCLCC grade, and tumor margin status were comparable between the two groups. Patients in the kidney capsule group had a higher rate of postoperative AKI without subsequent differences in the short-term and long-term outcomes. Theoretically, en bloc nephrectomy for perirenal RPS might secure a complete resection margin for local tumor control because, based on a previous meta-analysis, surgical margins correlate with OS and RFS21. Nevertheless, within the kidney capsule group, following a subgroup analysis, the baseline characteristics of both the nephrectomy and no-nephrectomy groups were similar, and nephrectomy resulted in comparable surgical margins, postoperative AKI, and short-term and long-term outcomes. Our surgical strategy for retroperitoneal LPS involving the kidney capsule achieved optimal short-term and survival outcomes without increasing the risk of subsequent renal impairment. There are several possible explanations for this observation. First, in this study, nephrectomy was performed in only 60% of the patients with kidney capsule involvement when the kidney was directly invaded by the tumor or the renal hilum or if more than half of the kidney was encased by the tumor. Thus, a kidney-sparing strategy was implemented in patients whose partial kidney capsules could be resected along with the mass without increasing morbidity. Second, it is difficult to distinguish LPS tumors from normal fat, and compartmental resection had an R0 resection rate of only 57% in a previous study22. Therefore, we also found that en bloc nephrectomy for patients with LPS and kidney capsule involvement did not improve the surgical margins in this study.

This study had certain limitations. First, the findings were limited by the retrospective study design and registry-level data analysis. However, this study included a large sample of patients with a solitary histology of LPS with long-term survival data. Additionally, subgroup analyses were conducted to investigate the impact of nephrectomy and tumor status. Second, in the present study, a limited number of patients were included because of the low incidence, so that no propensity score matching was performed, which might lead to bias. Finally, postoperative follow-up was also limited to clinical evaluation and contrast-enhanced computed tomography of the abdomen every 6–12 months after surgery, whereas renal function was not monitored; therefore, long-term progression of the CKD stage was not assessed. Nevertheless, we collected data on the permanent need for dialysis during the follow-up period.

Conclusion

In conclusion, this study showed largely comparable results with regard to clinical features and surgical outcomes in patients with retroperitoneal LPS involving the kidney capsule and those without kidney capsule involvement. The kidney-sparing strategy for retroperitoneal LPS involving the kidney capsule achieved optimal short-term and survival outcomes without increasing the risk of subsequent renal impairment. Additional prospective studies are warranted to confirm the reproducibility of these findings.

Ethical approval

This study was approved by the Institutional Review Boards of West China Hospital, Sichuan University (2023-1112).

Consent

Due to the study’s retrospective design, the requirement for informed consent was waived.

Source of funding

Not applicable.

Author contribution

Y.L.: methodology, data collection, analysis and interpretation, manuscript preparation, and critical review in the manuscript; Q.G.: conceptualization, supervision and guidance, methodology, critical review, data analysis, and manuscript writing; B.H. and J.Z.: data collection, analysis and interpretation, manuscript preparation, and critical review.

Conflicts of interest disclosure

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Research registration unique identifying number (UIN)

Name of the registry: the Chinese Clinical Trials Registry.

Unique identifying number or registration ID: ChiCTR2300076349.

Hyperlink to your specific registration (must be publicly accessible and will be checked): https://www.chictr.org.cn/showproj.html?proj=208360.

Guarantor

Qiang Guo, Division of Vascular Surgery, Department of General Surgery, West China Hospital, Sichuan University, Chengdu 610041, Sichuan Province, China. E-mail: rosebud1@163.com.

Data availability statement

The dataset generated and analyzed during the current study is not publicly available due to patient privacy restrictions and ongoing data collection for research purposes but are available from the corresponding author (Qiang Guo, rosebud-1@163.com) on reasonable request.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Supplementary Material

Acknowledgements

The authors thank D.Y. Kang, statistician of the Department of Evidence-based Medicine and Clinical Epidemiology, West China Hospital, Sichuan University, Chengdu, for his assistance with the statistical analysis. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

Supplemental Digital Content is available for this article. Direct URL citations are provided in the HTML and PDF versions of this article on the journal's website, www.lww.com/international-journal-of-surgery.

Published online 13 June 2024
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References

1 Zhao S Sun L Zhou J . Advancements in diagnosis and multimodal treatment strategies for retroperitoneal tumors: a comprehensive review. Am J Clin Oncol 2024;47 :350–356.38476111
2 Fairweather M Gonzalez RJ Strauss D . Current principles of surgery for retroperitoneal sarcomas. J Surg Oncol 2018;117 :33–41.29315649
3 Gorji L Nikahd M Onuma A . Comparing multivisceral resection with tumor-only resection of liposarcoma using the Win Ratio. Ann Surg Oncol 2024;31 :3389–3396.38347333
4 Villano AM Zeymo A Nigam A . Radical excision for retroperitoneal soft tissue sarcoma: a national propensity-matched outcomes analysis. Surgery 2020;168 :831–837.32709488
5 Chiappa A Bertani E Pravettoni G . Aggressive surgical approach for treatment of primary and recurrent retroperitoneal soft tissue sarcoma. Indian J Surg 2018;80 :154–162.29915482
6 Ikoma N Roland CL Torres KE . Concomitant organ resection does not improve outcomes in primary retroperitoneal well-differentiated liposarcoma: a retrospective cohort study at a major sarcoma center. J Surg Oncol 2018;117 :1188–1194.29228466
7 Cho CW Lee KW Park H . Clinical benefit and residual kidney function of en bloc nephrectomy for perirenal retroperitoneal sarcoma. Asia Pac J Clin Oncol 2018;14 :e465–e471.29044883
8 Stahl CC Schwartz PB Ethun CG . Renal function after retroperitoneal sarcoma resection with nephrectomy: a matched analysis of the united states sarcoma collaborative database. Ann Surg Oncol 2021;28 :1690–1696.33146839
9 Morizawa Y Miyake M Shimada K . Extended resection including adjacent organs and Ki-67 labeling index are prognostic factors in patients with retroperitoneal soft tissue sarcomas. World J Surg Oncol 2016;14 :43.26911364
10 Swallow CJ Strauss DC Bonvalot S . Management of primary retroperitoneal sarcoma (RPS) in the adult: an updated consensus approach from the Transatlantic Australasian RPS working group. Ann Surg Oncol 2021;28 :7873–7888.33852100
11 Mathew G Agha R Albrecht J . STROCSS 2021: strengthening the reporting of cohort, cross-sectional and case-control studies in surgery. Int J Surg 2021;96 :106165.34774726
12 Guillou L Coindre JM Bonichon F . Comparative study of the National Cancer Institute and French Federation of Cancer Centers Sarcoma Group grading systems in a population of 410 adult patients with soft tissue sarcoma. J Clin Oncol 1997;15 :350–362.8996162
13 Rodrigues FB Bruetto RG Torres US . Incidence and mortality of acute kidney injury after myocardial infarction: a comparison between KDIGO and RIFLE criteria. PLoS One 2013;8 :e69998.23894572
14 Pattaro C Riegler P Stifter G . Estimating the glomerular filtration rate in the general population using different equations: effects on classification and association. Nephron Clin Pract 2013;123 :102–111.23797027
15 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 :205–213.15273542
16 Terakawa T Taguchi I Imanishi O . A case of retroperitoneal liposarcoma arising from the renal capsule. Hinyokika Kiyo 2005;51 :171–173.15852670
17 Ishii K Yokoyama Y Nishida Y . Characteristics of primary and repeated recurrent retroperitoneal liposarcoma: outcomes after aggressive surgeries at a single institution. Jpn J Clin Oncol 2020;50 :1412–1418.32699905
18 Gaston KE White RL Jr Homsi S . Nephron-sparing radical excision of a giant perirenal liposarcoma involving a solitary kidney. Am Surg 2007;73 :377–380.17439032
19 Kim DB Gray R Li Z . Effect of nephrectomy for retroperitoneal sarcoma on post-operative renal function. J Surg Oncol 2018;117 :425–429.29044533
20 Hull MA Niemierko A Haynes AB . Post-operative renal function following nephrectomy as part of en bloc resection of retroperitoneal sarcoma (RPS). J Surg Oncol 2015;112 :98–102.26179132
21 Guo Q Zhao J Du X . Survival outcomes of surgery for retroperitoneal sarcomas: a systematic review and meta-analysis. PLoS One 2022;17 :e0272044.35901187
22 Santos CE Correia MM Thuler LC . Compartment surgery in treatment strategies for retroperitoneal sarcomas: a single-center experience. World J Surg 2010;34 :2773–2781.20645096
