Correlation between pre-treatment serum total blood bilirubin and unconjugated bilirubin and prognosis in patients with colorectal cancer

Hui Tong,Peng Xing,Zhao-Ning Ji

Abstract BACKGROUND Epidemiological studies have found that unconjugated bilirubin (UCB) levels are positively correlated with the incidence of colorectal cancer (CRC).Therefore,bilirubin may also play an important role in the prognosis of CRC.AIM To investigate the predictive value of total bilirubin (TBIL) and UCB in the prognosis of patients with CRC.METHODS A total of 142 CRC patients were selected as the research subjects in Jingxian Hospital,from October 2014 to May 2021.General and tumour-related clinical data at admission and the overall survival at 3 years after surgery were collected.The optimal cut-off values of TBIL and UCB were determined by receiver operating characteristic curve analysis.Univariate and multivariate Cox regression were used to analyse the effect of bilirubin level on the survival of CRC patients.The Kaplan-Meier method was used to assess the survival time.RESULTS The 3-year overall survival rate of CRC patients was significantly higher in the high TBIL (＞ 13.45 μmol/L) group than in the low TBIL (≤ 13.45 μmol/L) group(76.4% vs 37.1%;P ＜ 0.05).The 3-year overall survival rate of CRC patients in the high UCB (＞ 10.75 μmol/L) group was significantly higher than that in the low UCB (≤ 10.75 μmol/L) group (83.3% vs 34.2%;P ＜ 0.05).Multivariate Cox regression analysis showed that higher TBIL levels were an independent predictor of better prognosis in CRC patients (hazard ratio=0.360,95% confidence interval: 0.159-0.812,P=0.014).CONCLUSION TBIL levels can be used as a prognostic indicator for CRC patients.

Key Words: Bilirubin;Colorectal neoplasms;Prognosis

INTRODUCTION

Colorectal cancer (CRC) is the third most common cancer worldwide and the second leading cause of cancer-related death[1].The incidence of CRC is higher in men than in women.The CRC burden is expected to increase by 60%,with more than 2.2 million new cancer cases and more than 1.1 million cancer deaths,by 2030[2].

Some studies have reported that bilirubin,a product of haemoglobin catabolism,and particularly unconjugated bilirubin (UCB),has significant anti-inflammatory and anti-oxidant effects and that it plays a role in several oxidative stress-related diseases,including CRC[3].Epidemiological studies have found that,in men,UCB levels are positively correlated with the incidence of CRC,while they are negatively correlated with the incidence of CRC in women[4,5].

However,clinical data on the relationship between UCB levels and CRC prognosis are lacking.Therefore,this study aimed to investigate the effect of serum total bilirubin (TBIL) and UCB levels on the prognosis of patients with CRC.

MATERIALS AND METHODS

General information

Patients with CRC who attended Jingxian Hospital between October 2014 and May 2021 were selected.The clinical data of 142 study subjects who met the inclusion criteria were retrospectively analysed.Patient inclusion criteria were as follows: (1) Age ＞ 18 years without preoperative antitumor treatment;(2) radical resection of primary CRC;(3)histopathology-confirmed diagnosis of all patients with stage I-III CRC;and (4) complete clinical and pathological data.Patient exclusion criteria were as follows: (1) Colon perforation and peritonitis;(2) history of oncological disease and death from other causes during follow-up;(3) severe cardiovascular disease;(4) primary hepatobiliary diseases that may affect serum bilirubin levels;and (5) incomplete data.

Among the 142 patients finally included,91 were male and 51 were female,with an average age of (64.11 ± 9.10) years and a follow-up period of (5 to 49 mo).Clinical data of the study subjects at the time of admission were collected by reviewing electronic records.These data included age,sex,smoking status,tumour differentiation,tumour size,tumour location,tumour,node,and metastasis (TNM) staging,and laboratory test data (imaging examination,etc).Fasting peripheral blood samples were obtained from patients before surgery to determine TBIL and UCB levels.

Follow-up methods

Patients included in the study were followed up by telephone,or at inpatient or outpatient visits,starting from the time of patient discharge,with a follow-up interval of once every 2 mo.Patient survival and other conditions were followed up until the patient’s death or the study endpoint (October 31,2022).

Statistical analysis

SPSS v22.0 (IBM SPSS Inc.,Armonk,NY,United States) was used for statistical analysis of the data.Normally distributed quantitative data are expressed as mean ± SD and were compared between the two groups usingt-tests.Quantitative data with a skewed distribution are expressed as median (interquartile interval) and were compared between the two groups using the non-parametric Mann-Whitney U test.Count data were expressed as composition ratios and were compared using the Chi-Square test.Survival curves were plotted using the Kaplan-Meier method and differences in survival between groups were analysed using the log-rank test.A Cox regression model was used to analyse the risk factors affecting disease prognosis.APvalue of less than 0.05 was considered statistically significant.

RESULTS

Determination of optimal cut-off values for TBIL and UCB

To determine the optimal cut-off values for TBIL and UCB,the area under the receiver operating characteristic (ROC)curve for prediction of survival in CRC patients was fitted.The area under the ROC curve predicted by TBIL was 0.660[95% confidence interval (CI): 0.565-0.755;P=0.001],with a sensitivity of 67.9% and specificity of 72.1%.The maximum Youden index value was 0.400 at a cut-off value of 13.45 μmol/L for TBIL for dividing CRC patients into high TBIL (＞13.45 μmol/L) and low TBIL (≤ 13.45 μmol/L) groups.The area under the ROC curve predicted by UCB was 0.735(95%CI: 0.646-0.82;P＜ 0.001),with a sensitivity of 67.9% and a specificity of 82.0%.The maximum Youden index value was 0.499 at a cut-off value of 10.75 μmol/L for UCB for dividing CRC patients into high UCB (＞ 10.75 μmol/L) and low UCB (≤ 10.75 μmol/L) groups (Table 1).

Relationship between TBIL level grouping and basic clinical characteristics

The differences between the two groups in the degree of tumour differentiation,presence of lymph node metastasis and pathological TNM stage were statistically significant (P＜ 0.05).However,there were no statistically significant differences (P＞ 0.05) in age,sex,tumour diameter,tumour location,chemotherapy,and smoking ratio (Table 2).

Table 2 Relationship between total bilirubin level grouping and basic clinical characteristics of patients (mean ± SD)

Survival curve analysis of the TBIL and UCB groups

The 3-year overall survival rate was 37.1% (26/70) in the low TBIL group and 76.4% (55/72) in the high TBIL group,which was statistically significantly different (P＜ 0.001).The 3-year overall survival rate was 34.2% (26/76) in the low UCB group and 83.3% (55/66) in the high UCB group,with a statistically significant difference between the two groups (P＜ 0.001),as shown in Figure 1.

Figure 1 Survival curve analysis of colorectal cancer patients in the total bilirubin and unconjugated bilirubin groups. A: Colorectal cancer(CRC) patients in the total bilirubin group;B: CRC patients in the unconjugated bilirubin group.TBIL: Total bilirubin;UCB: Unconjugated bilirubin.

Cox regression analysis of factors affecting the prognosis of CRC patients

Cox univariate regression analysis was performed on variables collected in this study that had the potential to affect the prognosis of patients,including age and sex.The analysis showed that the degree of tumour differentiation,tumour diameter,lymph node metastasis,pathological stage,smoking,TBIL,and UCB were associated with prognosis (P＜ 0.05).Variables with statistically significant differences were further included in the multivariate regression analysis.The results showed that the degree of tumour differentiation,lymph node metastasis,and TBIL were risk factors affecting the prognosis of patients (P＜ 0.05),as shown in Table 3.

Table 3 Cox regression analysis affecting the prognosis of colorectal cancer patients

DISCUSSION

In this study,we demonstrated that bilirubin levels may be used as a prognostic indicator in CRC patients.Higher TBIL and UCB levels were negatively correlated with 3-year survival in CRC.TBIL may be used as a protective prognostic indicator in patients with CRC.

Bilirubin is a product of secondary catabolism of haemoglobin,which is released during the breakdown of aging red blood cells.Bilirubin is present in the circulation mainly in the form of TBIL,direct bilirubin,and UCB[6].Although abnormally high concentrations of bilirubin are considered harmful,mildly to moderately elevated serum bilirubin concentrations can act as a potent endogenous anti-oxidant with anti-inflammatory,anti-oxidant,and anti-proliferative effects through the process of oxidation of bilirubin itself to biliverdin[7].Recent evidence suggests that mildly elevated levels of bilirubin,a novel metabolic hormone,may have a protective role in cardiovascular disease and cancer[8].Several studies have shown a close relationship between serum bilirubin levels and digestive system tumours.Sunetal[9] found that low TBIL levels were associated with poor prognosis in gastric cancer,but other studies have shown that high levels of TBIL are a risk factor for poor tumour prognosis[10].

Studies have reported inconsistent results regarding the relationship between circulating bilirubin levels and risk of CRC.In a Mendelian randomization study (67878 cases),TBIL levels were not associated with the risk of CRC[11],which was similar to the findings of a meta-analysis and a prospective survey[12,13].In an approximately 10-year follow-up study by Heetal[14],baseline TBIL levels were found to be negatively correlated with the risk of CRC.On the other hand,a nested case-control study by McCulloughetal[15] found a positive correlation between TBIL levels and the risk of CRC.Although the relationship between bilirubin levels and the risk of CRC remains inconclusive,its potential predictive value for the prognosis of CRC remains a hot topic in the field.

In a prospective study,combining preoperative albumin with bilirubin could predict postoperative complications and overall survival in CRC patients,particularly in stage III patients with tumour metastasis[16].In the present study,we found that CRC patients with lower levels of TBIL had a worse prognosis and that a lower TBIL level was an independent risk factor for poor survival outcomes in CRC patients,which was consistent with the findings of Sunetal[9].On the other hand,Yangetal[17] found that increased TBIL was associated with decreased overall survival in CRC patients.The difference between our study findings and those of Yangetal[17] may be related to the inclusion of different study subjects,as their study subjects consisted of stage IV CRC patients,while our study subjects did not include stage IV patients.

UCB,which is the most active anti-oxidant component of TBILinvitro,comprises a large part of circulating bilirubin[18].In the present study,lower UCB levels were associated with lower survival rates in CRC patients in univariate,but not in multivariate Cox regression analysis,similar to previous findings[19].This suggests that UCB,as a prognostic factor,is influenced by other factors and is not suitable as an independent predictor in clinical practice.

In conclusion,our results indicate that circulating TBIL may be used as a prognostic indicator in CRC patients.However,due to the retrospective nature of this study and the small sample size,larger prospective studies are still needed to confirm these findings.

CONCLUSION

TBIL levels can be used as a prognostic indicator for CRC patients.

ARTICLE HIGHLIGHTS

Research background

Epidemiological studies have found that unconjugated bilirubin (UCB) levels are positively correlated with the incidence of colorectal cancer (CRC).

Research motivation

Therefore,we speculate that bilirubin may also play an important role in the prognosis of CRC.

Research objectives

To investigate the predictive value of total bilirubin (TBIL) and UCB in the prognosis of patients with CRC.

Research methods

A total of 142 CRC patients were selected as the research subjects in Jingxian Hospital,from October 2014 to May 2021.General and tumour-related clinical data at admission and the overall survival at 3 years after surgery were collected.The optimal cut-off values of TBIL and UCB were determined by receiver operating characteristic curve analysis.Univariate and multivariate Cox regression were used to analyse the effect of bilirubin level on the survival of CRC patients.The Kaplan-Meier method was used to assess the survival time.

Research results

The 3-year overall survival rate of CRC patients was significantly higher in the high TBIL (＞ 13.45 μmol/L) group than in the low TBIL (≤ 13.45 μmol/L) group (76.4%vs37.1%;P＜ 0.05).The 3-year overall survival rate of CRC patients in the high UCB (＞ 10.75 μmol/L) group was significantly higher than that in the low UCB (≤ 10.75 μmol/L) group (83.3%vs34.2%;P＜ 0.05).Multivariate Cox regression analysis showed that higher TBIL levels were an independent predictor of better prognosis in CRC patients (hazard ratio=0.360,95% confidence interval: 0.159-0.812,P=0.014).

Research conclusions

TBIL levels can be used as a prognostic indicator for CRC patients.

Research perspectives

To investigate the role of TBIL and UCB in the prognosis of patients with CRC.

FOOTNOTES

Author contributions:Ji ZN designed the research;Tong H performed the research;Ji ZN and Xing P contributed new reagents or analytic tools;Tong H analyzed data and wrote the paper.

Institutional review board statement:This study was reviewed and approved by the Ethics Committee of Jingxian Hospital in Anhui Province.

Informed consent statement:As the study used anonymous and pre-existing data,the requirement for informed consent from patients was waived.

Conflict-of-interest statement:We have no financial relationships to disclose.

Data sharing statement:No additional data are available.

Open-Access:This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers.It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license,which permits others to distribute,remix,adapt,build upon this work non-commercially,and license their derivative works on different terms,provided the original work is properly cited and the use is non-commercial.See: https://creativecommons.org/Licenses/by-nc/4.0/

Country/Territory of origin:China

ORCID number:Zhao-Ning Ji 0009-0000-0440-3892.

S-Editor:Qu XL

L-Editor:Webster JR

P-Editor:Zhang YL