Prognostic Effect of Preoperative Apolipoprotein B Level in Surgical Patients with Renal Clear Cell Carcinoma

Objectives To assess the prognostic value of preoperative apolipoprotein B level in surgical patients with renal clear cell carcinoma (ccRCC). Materials and Methods The study included 308 ccRCC patients receiving radical or partial nephrectomy between 2003 and 2012 in our center. The correlations among the preoperative ApoB, clinico -pathological parameters, and overall survival (OS) were evaluated. Results A total of 193 men (62.9%) and 114 women (37.1%) with ccRCC underwent radical or partial nephrectomy were enrolled in the present study. The OS at ve years after operation was 90.6% for all patients, 87.4% for the lower ApoB group, and 97.0% for the higher ApoB group. The CSS at 5 years after surgery was 90.2% for all patients, 86.7% for the lower ApoB group, and 97.0% for the higher ApoB group. A higher ApoB level was related to a better OS and CSS in ccRCC patients (P = 0.001 and P < 0.001, respectively). In multivariate analysis, age >60 (P=0.008 and P=0.023), lower Apo B level (P= 0.019 and P= 0.018), were independent prognostic factors for OS and CSS, respectively. Conclusions In the Apo apolipoprotein family, the preoperative ApoB level has an important clinical signicance for predicting the prognosis survival rate of the ccRCC patients. the Kaplan-Meier log-rank analysis of related to help of Mantel-Cox regression methodology. hazards multivariate compare the under the curve (AUC). square used to the two-sided and a P-value <0.05 statistically data SPSS Statistics A-I and ApoL1 had an anti-tumor effect, there were no related experiment studies confirm their effect in renal clear cell carcinoma. Moreover, no clinical trials revealed the high level of Apo A-I and ApoL1 was associated with the high survival rate of renal cancer. However, the relation between the two and the prognosis of renal clear cell carcinoma could be researched in the future.


Background
Renal cell cancer is a common kind of urinary tumor and accounts for 2-3% of all cancers [ 1]. More than 80% of them are clear cell carcinoma, and other histological types are very rare [ 2]. Surgery has been the benchmark for the treatment of RCC [ 3]. However, preoperative judgment of the patient's prognosis is very important for patients and clinicians [ 4]. Although there are already some indicators that could predict the prognosis [ 5,6], such as TNM stage, Fuhrman grade and CRP/Alb ratio, simple biomarkers are still lacking for early diagnosis and the judgment of prognosis in clinical practice.
Apolipoprotein ApoB is a newly discovered potential tumor marker that plays an important role in lipoprotein metabolism and participates in the reverse transport of cholesterol [ 7]. There are different degrees of ApoB elevation in the patient's serum of liver cancer, breast cancer and ovarian cancer [ 8,9] . The changes of ApoB level had an important value for the prognosis of the above tumors. Therefore, in this study we aim to explore the prognostic performance of the preoperative ApoB level in Chinese patients with ccRCC.

Patients
The data of 414 ccRCC patients which underwent radical or partial nephrectomy in The Third Affiliated Hospital of Soochow University between 2003 and 2012 were collected in our study. Of all 414 patients, 106 patients were excluded: 36 patients had concomitant chronic diseases, including diabetes, hyperlipidemia and metabolic syndrome; 17 patients had been lost in the follow-up time; 17 patients' information on were incomplete and unclear; 36 patients had received drug therapy previously. Finally, the 308 patients were identified for related analysis.

Clinical and laboratory data
The characteristics and information of each patient included in our study were summarized: age at surgery, gender, TNM stage, Fuhrman grade, tumor necrosis and tumor size, LVI and LDH and AKP. The 2010 renal TNM stage by AJCC was adopt [ 10]. Fuhrman grade was recommended by WHO in 1997. Tumor necrosis was defined as microscopic Page 3/11 coagulative necrosis [ 11]. The data of LVI, LDH and AKP were obtained within 1 week before surgery. All of the above data above were retrieved from Medical records inquiry system of The Third Affiliated Hospital of Soochow University.

Statistical analyses
For the description of clinical and pathological characteristics of patients, categorical variables were presented as numbers and percentages, continuous variables were allocated in groups according to the optimal cut-off value.
Receiver operating characteristics (ROC) analysis was done to identify the cutoff point of continuous variables. OS was calculated from date of surgery to individuals' death of any cause or last follow-up. The OS rates were calculated using the Kaplan-Meier method, and compared using the log-rank test. Univariate analysis of the potential factors related to survival was conducted with the help of Mantel-Cox regression methodology. The Cox proportional hazards model was used for the multivariate analysis to identify independent prognostic factors associated with OS. ROC analysis was also used to measure and compare the areas under the curve (AUC). The Chi square test was used to detect the differences between groups. All statistical tests were two-sided and a P-value <0.05 was considered statistically significant. All data analyses were performed with SPSS Statistics 17.0.  Table 1 showed the relationships between ApoB levels and the clinicopathological characteristics of the all CCRCC patients included in the study. There were no signi cant differences with regard to age, sex, tumor size, tumor stage, lymph node stage, Fuhrman grade, the presence of Tumor necrosis, lymphovascular invasion, LDH and AKP levels between the two groups. Therefore, we did not conduct the propensity score-matched analysis for ApoB. Figure 1 shows the Kaplan-Meier survival curve for CSS and OS according to ApoB level. The OS at ve years after operation was 90.6 % for all patients, 87.4 % for the lower ApoB group, and 97.0 % for the higher ApoB group. The CSS at 5 years after surgery was 90.2 % for all patients, 86.7 % for the lower ApoB group, and 97.0 % for the higher ApoB group. A higher ApoB level was related to a better OS and CSS in ccRCC patients (P = 0.001 and P < 0.001, respectively).  (Table 2) and CSS (Table 3), respectively. In multivariate analysis, age >60 (P=0.008 and P=0.023), lower Apo B level (P= 0.019 and P= 0.018), were independent prognostic factors for OS (Table 2) and CSS (Table 3), respectively.

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For renal clear cell carcinoma, a simple biomarker for early diagnosis and prognosis is still lacking in clinical practice.
Through our research, it is found that apolipoprotein ApoB is of great significance.
Previous literature [ 12] reported that ApoB, SLC3A1, SCD5, and AQP1 genes could be used as prognostic biomarkers for renal clear cell carcinoma, and the four genes had different powers that judged the prognosis. However, the specific effect of ApoB was not illuminated.
Renal clear cell carcinoma is a malignant tumor composed of cells whose cytoplasm is transparent [ 13]. And cancer cells are rich in cholesterol and cholesterol esters [ 14,15]. In 1987, it was firstly reported by Gcbhard et al [ 15]. that the levels of cholesterol and cholesterol esters in renal cell carcinoma were higher than those in normal kidney tissues.
Subsequently, some experimental studies also confirmed the above result and further found that the level of cholesterol was positively associated with the malignant degree of cancer cells [ 16,17]. However, the cholesterol levels in advanced biological cells are maintained in a fairly narrow range, and the negative feedback regulation of endogenous cholesterol synthesis play an important role in maintaining the cholesterol metabolic balance [ 18,19]. And the biological effect of serum cholesterol was related with low-density lipoprotein (LDL) [ 20]. It was manifested by the fact that about two-thirds of endogenous cholesterol were transported by LDL [ 21]. Therefore, we concluded that if the cholesterol level in renal cancer tissues increased significantly with the malignant degree elevating, the negative feedback regulation could inhibit the synthesis and transport of endogenous cholesterol, and this indirectly resulted that the level of LDL decreased.
In our study, patients with the high level of preoperative ApoB had a higher survival rate than those with the low level of preoperative ApoB. We considered this was mainly related with the level of LDL metabolism. ApoB is an important structural component of LDL [ 22]. According to the above analysis, the negative feedback regulation caused by the Apolipoprotein ApoB acts indirectly by reflecting the LDL levels, so why not to directly adopt the LDL levels as the prognostic index? The reasons maybe are as followings: the small, dense low-density lipoprotein (sd-LDL) is difficult to detect in the blood [ 23], but as its structural component ApoB can be simply detected in the blood. Thus, apolipoprotein ApoB has become a more advantageous detection index by more comprehensively reflecting the LDL level.
In addition, we considered that in a nutritional perspective patients with the high level of preoperative ApoB should also have a higher survival rate. The reasons were as followings: the level of ApoB represented the nutritional level of the patient to some extent [ 24]. And the nutritional level of the patient determined the body resistance [ 25]. When the body resistance increased, the capability of tumor tolerance and the prognosis survival rate also elevated.
Some trials documented that in the apolipoprotein family Apo A-I and ApoL1 had an anti-tumor effect [ 26]. But the mechanism of the two were different. Recently, researchers used ApoA-I mimetic peptides to observe the association between ApoA-I and ovarian cancer cells [ 27]. ApoA-I mimetic peptides reduced viability and proliferation of ID8 cells Our research has several shortcomings. Firstly, it is only a single-center study. In the future, we would collect more samples by multi-centers cooperation to carry out related research. Secondly, we only include renal clear cell carcinoma, and we would further explore the predictive significance of ApoB in other types of kidney cancer in the future.

Conclusion
Conclusively, in the Apo apolipoprotein family, the preoperative ApoB level has an important clinical significance for predicting the prognosis survival rate of the ccRCC patients.

Declarations
Ethics approval and consent to participate We declare that our research has been performed in accordance with the Declaration of Helsinki and has been approved by the ethics committee of the Third Affiliated Hospital of Soochow University.

Consent to publish
We confirm that we have obtained the consent of the persons for publication.

Availability of data and materials
We ensure that materials described in the manuscript, including all relevant raw data, will be freely available to any scientist wishing to use them for non-commercial purposes, without breaching participant confidentiality..

Competing interests
We declare that they have no competing interests

Funding
We have no funding supports.

Authors Contributions
WK and CZ conceived and designed the study. W TC and C YM performed the study. provided the mutants. WK wrote the paper. S GL and H XZ reviewed and edited the manuscript. All authors read and approved the manuscript.    Figure 1 The Kaplan-Meier survival curves according to the preoperative apolipoprotein B level. The OS and CSS rates were signi cantly higher in the high Apo B level group compared with the low group (P = 0.001 and P < 0.001, respectively).