Colorectal cancer (CRC) is among the most frequently diagnosed cancers in the United States (US) [
The classic tumor, node, and metastasis (TNM) staging system is regarded as the standard prognostic parameter and forms the basis for treatment decisions in CRC [
In recent years, increasing attention has been given to the role of mucins (MUC) in the pathogenesis of cancer. MUC are a family of high molecular weight glycosylated proteins [
Evidence suggests that MUC expression is involved in the invasion and metastasis of various malignancies, including gallbladder cancer [
This systematic review and meta-analysis is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline [
Two review authors independently searched the PubMed, Embase, Cochrane Library, and Web of Science databases from inception through September 13, 2019. Keywords included (“mucins” OR “mucin” OR “MUC”) AND (“colorectal cancer” OR “colorectal neoplasm” OR “colorectal tumor” OR “colonic cancer” OR “colon cancer” OR “rectal cancer” OR “CRC”) AND (“prognostic “OR “prognosis” OR “outcome” OR “survival”). A manual search of the reference lists of relevant articles was performed. Searches were limited to articles published in English or Chinese language.
The inclusion criteria were (1) study design: cohort study; (2) population: patients with CRC; (3) parameter: MUC expression levels in CRC tissues; and (4) outcome: association between MUC expression levels in CRC tissues and prognosis.
The exclusion criteria were as follows: (1) duplicate publications; (2) in vitro or animal studies; (3) reviews, conference reports, meta-analyses, books, case reports, or letters; or (4) studies that reported insufficient data. When articles reported data from the same study, the most recent article was included.
Two review authors independently extracted data from the eligible studies, including the surname of the first author, year, country, sample size, patients’ mean age, MUC phenotype, antibody for MUC, cut-off value for MUC, frequency of high MUC expression, detection method, TNM stage, histologic type, mean tumor dimensions, median follow-up, and outcomes. Disagreements about data extraction were resolved by discussion with a third reviewer until consensus was reached.
Two review authors independently conducted an assessment of the methodological quality of included studies using the Newcastle Ottawa Scale (NOS) [
Publication bias was evaluated using Egger’s linear regression and Begg’s rank correlation test [
Statistical analyses were performed using Review Manager, version 5.3 (Cochrane Collaboration, Copenhagen, Denmark) and STATA, version 12.0 (Stata Corporation, College Station, TX, USA). Survival analysis was performed according to Moher et al. [
Studies with significant heterogeneity were identified with the chi-squared test (
A total of 1273 articles were identified from the electronic search of the databases, and 3 additional studies were obtained from the manual search of the reference lists of relevant articles. After excluding 492 duplicates, titles and abstracts were screened, and 726 studies that did not meet the inclusion criteria were excluded. The full text of 58 studies was retrieved for further review, and 8 articles that did not report an endpoint, 8 articles with insufficient data, and 9 conference abstracts were excluded. Finally, 33 observational studies [
Flow diagram of included studies.
The characteristics of the included studies are shown in Table
Characteristics of the included studies.
First author | Year | Country | Patient number | Detection method | Mean age (years) | Media follow-up (mounts) | Outcome | Mucins phenotype | Antibody | Cut-off value (high level) | High MUC expression |
---|---|---|---|---|---|---|---|---|---|---|---|
Adams | 2009 | Switzerland | 938 | IHC | 70.5 | 128.0 | OS | MUC2 | NR | NR | |
Al-Maghrabi | 2019 | Saudi Arabia | 128 | IHC | NR | NR | OS/DFS | MUC2 | MRQ-18 | 36.7% | |
Baldus | 2000 | Germany | 264 | IHC | 64.8 | NR | OS | MUC1 | NCL-MUC1 | 58.0% | |
Baldus | 2004 | Germany | 205 | IHC | 65.0 | NR | OS | MUC1 | HMFG-2 | 49.8% | |
Betge | 2016 | Germany | 381 | IHC | 68.5 | NR | OS/DFS | MUC1 | Ma695 | 64.0% | |
MUC2 | Ccp-58 | 77.0% | |||||||||
MUC5AC | 45M1 | 48.9% | |||||||||
MUC6 | MCN6.01 | 28.7% | |||||||||
Dawson | 1987 | UK | 358 | IHC | 65.7 | 18.0 | OS | Sialomucin | High iron diamine-alcian blue | Blue staining | 29.6% |
Diaz | 2018 | Spain | 96 | IHC | 65.9 | NR | DFS | MUC1 | Clone E29 | 46.0% | |
Duncan | 2007 | UK | 403 | IHC | 72.0 | 116.0 | OS | MUC1 | Ma695 | 31.5% | |
MUC3 | 1143/B7 | 73.9% | |||||||||
Elzagheid | 2013 | Libya | 141 | IHC | NR | 77.0 | OS/DFS | MUC2 | MRQ-18 | 50.0% | |
Hiraga | 1998 | Japan | 100 | IHC | 62.7 | 80.0 | OS | MUC1 | KL-6 | 71.0% | |
Imai | 2013 | Japan | 250 | IHC | 66.9 | NR | OS/RFS | MUC2 | Ccp-58 | 49.4% | |
MUC5AC | CLH2 | 46.8% | |||||||||
Ionescu | 2014 | Romania | 39 | qRT-PCR | 66.0 | NR | OS | MUC12 | NR | NR | NR |
Kang | 2011 | Korea | 229 | IHC | NR | 108 | OS | MUC2 | NR | 24.2% | |
Kasprzak | 2018 | Poland | 34 | IHC | NR | NR | OS | MUC1 | Ma552 | 100% | |
MUC2 | Ccp-58 | 100% | |||||||||
Khanh | 2013 | Japan | 206 | IHC | NR | NR | OS/RFS | MUC1 | Ma695 | 62.6% | |
MUC2 | Ccp-58 | 32.5% | |||||||||
MUC4 | 1G8 | 33.0% | |||||||||
MUC5AC | CLH2 | 33.5% | |||||||||
Kimura | 2000 | Japan | 110 | IHC | 63.1 | 68.5 | OS | MUC1 | KL-6 | 69.1% | |
Kocer | 2002 | Turkey | 41 | IHC | 56.3 | NR | DFS | MUC5AC | 45M1 | 34.1% | |
Kocer | 2006 | USA | 30 | IHC | 59.0 | 39.0 | OS | MUC5AC | 45M1 | 60.0% | |
Lennerz | 2016 | USA | 33 | IHC | 58.0 | 51.2 | OS | MUC2 | Ccp58 | 84.0% | |
MUC5AC | CLH2 | 45.0% | |||||||||
MUC6 | CLH5 | 0.0% | |||||||||
Manne | 2000 | USA | 166 | IHC | 65.3 | NR | OS | MUC1 | DF3 | 39.8% | |
MUC2 | Ccp58 | 80.7% | |||||||||
Matsuda | 2010 | 569 | IHC | 68.0 | NR | OS | MUC2 | Anti-MUC2 | 65.0% | ||
MUC5AC | Anti-MUC5 | 15.1% | |||||||||
MUC6 | Anti-MUC6 | 1.9% | |||||||||
Matsuyama | 2010 | Japan | 100 | qRT-PCR | 65.1 | 27.0 | DFS | MUC12 | Rabbit polyclonal antibody | NR | NR |
Perez | 2008 | Brazil | 35 | IHC | 62.2 | NR | OS/DFS | MUC1 | Ma695 | 20.0% | |
MUC2 | Ccp-58 | 65.7% | |||||||||
MUC5AC | CLH2 | 22.9% | |||||||||
Shanmugam | 2010 | USA | 132 | IHC | 65.0 | NR | OS | MUC4 | Clone 8G7 | 24.2% | |
Sun | 2018 | China | 118 | IHC | 54.3 | 57.0 | OS/DFS | MUC1 | MXB Biotechnologies | 14.4% | |
Streppel | 2012 | USA | 39 | IHC | 63.6 | NR | OS | MUC16 | Monoclonal antibody | 64.1% | |
Wang | 2016 | China | 81 | IHC | 63.5 | NR | OS | MUC1 | ZM-0391 | 53.1% | |
Wang | 2017 | China | 139 | IHC | NR | NR | OS | MUC2 | NCL-MUC2 | 48.2% | |
MUC5AC | NCL-MUC5 | 28.1% | |||||||||
Xiao | 2013 | China | 150 | IHC | 55.0 | NR | OS/DFS | MUC20 | Mouse antihuman polyclonal antibody | 60.7% | |
You | 2006 | China | 203 | IHC | NR | 111.9 | OS | MUC1 | Ma695 | 40.7% | |
Yu | 2007 | China | 150 | IHC | 57.5 | NR | OS | MUC1 | Ma695 | 45.3% | |
MUC2 | Ccp-58 | 52.6% | |||||||||
MUC5AC | 45M1 | 44.0% | |||||||||
Zhang | 2008 | Japan | 77 | IHC | 64.9 | NR | OS | MUC1 | KL-6 | SI (positive) | 55.8% |
Zwenger | 2014 | Argentina | 90 | IHC | NR | NR | OS | MUC1 | HMFG1 | 94.0% | |
MUC2 | H300 | 52.4% |
NR: not reported; RT-PCR: reverse transcriptase polymerase chain reaction; IHC: immunohistochemistry; SI: staining intensity; PP: positive cell percentage; immunostaining score (ISS): PP
According to the NOS, all included studies were of high methodological quality (
The association between MUC expression levels in CRC tissues and OS was investigated in 41 datasets from 30 articles; each dataset represented various MUC phenotypes. The meta-analysis demonstrated no association between combined MUC phenotype expression levels and OS (
MUC expression and OS.
The association between MUC expression level in CRC tissues and DFS/RFS was investigated in 19 datasets from 11 articles. The meta-analysis demonstrated no association between combined MUC phenotype expression levels and DFS/RFS (
MUC expression and DFSRFS.
The meta-analysis demonstrated no association between combined MUC phenotype expression levels and CRC clinicopathological characteristics. In all analyses, there was evidence of significant heterogeneity between studies. The source of the heterogeneity was investigated in subgroup analyses stratified by specific MUC phenotype (Table
Meta-analysis of the correlation between MUC expression and clinicopathological factors of colorectal cancer.
Clinicopathological parameter | Mucins phenotype | No. of studies | OR (95% CI) | Analysis model | Test for overall effect | Heterogeneity | ||
---|---|---|---|---|---|---|---|---|
TNM stage (III/IV vs. I/II) | MUC1 | 11 | 2.17 (1.31-3.59) | Random | 3.03 | 0.002 | 83 | <0.00001 |
MUC2 | 7 | 0.52 (0.36-0.76) | Random | 3.35 | 0.0008 | 52 | 0.05 | |
MUC5AC | 8 | 1.00 (0.67-1.49) | Random | 0.01 | 0.99 | 55 | 0.03 | |
Depth of invasion (T3/T4 vs. T1/T2) | MUC1 | 11 | 1.79 (1.41-2.26) | Fixed | 4.86 | <0.00001 | 40 | 0.08 |
MUC2 | 6 | 0.65 (0.37-1.13) | Random | 1.53 | 0.13 | 63 | 0.02 | |
MUC5AC | 4 | 0.64 (0.35-1.18) | Random | 1.42 | 0.15 | 61 | 0.05 | |
Lymph node metastasis (+ vs. -) | MUC1 | 10 | 2.45 (1.38-4.35) | Random | 3.07 | 0.002 | 81 | <0.00001 |
MUC2 | 8 | 0.59 (0.47-0.73) | Fixed | 4.64 | <0.00001 | 48 | 0.06 | |
MUC5AC | 7 | 1.07 (0.67-1.72) | Random | 0.29 | 0.77 | 67 | 0.006 | |
Tumor site (colon vs. rectum) | MUC1 | 7 | 0.79 (0.63-0.98) | Fixed | 2.12 | 0.03 | 0 | 0.63 |
MUC2 | 5 | 1.64 (1.01-2.67) | Random | 2.02 | 0.04 | 55 | 0.06 | |
MUC5AC | 6 | 1.97 (1.48-2.62) | Fixed | 4.63 | <0.00001 | 49 | 0.08 | |
Distant metastasis (+ vs. -) | MUC1 | 3 | 2.47 (1.47-4.13) | Fixed | 3.43 | 0.0006 | 49 | 0.14 |
MUC2 | 3 | 0.83 (0.48-1.41) | Fixed | 0.70 | 0.49 | 0 | 0.61 | |
MUC5AC | 2 | 0.86 (0.15-4.87) | Random | 0.17 | 0.87 | 73 | 0.06 | |
Lymphatic invasion (+ vs. -) | MUC1 | 5 | 3.39 (1.69-9.14) | Random | 3.19 | 0.001 | 72 | 0.007 |
MUC2 | 3 | 0.53 (0.27-1.03) | Random | 1.88 | 0.06 | 60 | 0.08 | |
MUC5AC | 4 | 0.76 (0.55-1.05) | Fixed | 1.64 | 0.10 | 20 | 0.29 | |
Mucinous component (high vs. low) | MUC1 | 7 | 0.71 (0.42-1.19) | Random | 1.31 | 0.19 | 59 | 0.02 |
MUC2 | 2 | 14.46 (1.71-121.97) | Random | 2.46 | 0.01 | 59 | 0.12 | |
MUC5AC | 3 | 1.41 (0.85-2.34) | Fixed | 1.32 | 0.19 | 0 | 0.62 | |
Gender (male vs. female) | MUC1 | 7 | 1.10 (0.86-1.41) | Fixed | 0.77 | 0.44 | 0 | 0.75 |
MUC2 | 7 | 0.87 (0.68-1.12) | Fixed | 1.07 | 0.29 | 8 | 0.29 | |
MUC5AC | 6 | 0.93 (0.69-1.24) | Random | <0.00001 | 1.00 | 55 | 0.005 | |
Tumor size (large vs. small) | MUC1 | 4 | 0.77 (0.53-1.12) | Fixed | 1.38 | 0.17 | 19 | 0.30 |
MUC2 | 2 | 0.70 (0.47-1.05) | Fixed | 1.73 | 0.08 | 0 | 0.39 | |
MUC5AC | 2 | 0.80 (0.48-1.32) | Fixed | 0.87 | 0.38 | 0 | 0.41 | |
Histological grade (3 vs. 1 and 2) | MUC1 | 12 | 1.39 (0.87-2.21) | Random | 1.39 | 0.16 | 66 | 0.0007 |
MUC2 | 7 | 0.75 (0.56-0.99) | Fixed | 2.02 | 0.04 | 44 | 0.10 | |
MUC5AC | 5 | 1.44 (0.70-2.97) | Random | 0.99 | 0.32 | 79 | 0.0007 |
RR: risk ratio; Random: random effects model; Fixed: fixed.
A high level of MUC1 expression (III/IV vs. I/II:
A high level of MUC1 expression (T3/T4 vs. T1/T2:
A high level of MUC1 expression (positive vs. negative:
A high level of MUC1 expression (positive vs. negative:
A high level of MUC1 expression was associated with distant metastasis (positive vs. negative:
There were no associations between the expression levels of any MUC phenotypes and other clinicopathological characteristics, including gender or tumor size.
Sensitivity analysis omitting one study at a time demonstrated the associations of MUC family members’ expression with OS (Figure
Sensitivity analysis for MUC expression ((a): MUC1, (b): MUC2, (c): MUC5AC, (d): Others MUC) and OS.
Sensitivity analysis for MUC expression ((a): MUC1, (b): MUC2, (c): MUC5AC, (d): Others MUC) and DFS/RFS.
Publication bias for MUC expression ((a): MUC1, (b): M UC2, (c): MUC5AC, (d): Others MUC) and OS.
Publication bias for MUC expression ((a): MUC1, (b): MUC2, (c): MUC5AC, (d): Others MUC) and DFS/RFS.
Metaregression was performed to explore the factors influencing the association of MUC expression with OS and DFS/RFS in CRC. None of the covariates (cut-off value, antibody, TNM stage, country, and years) analyzed were identified as potential sources of heterogeneity (Table
Results of meta-regression analysis exploring the source of heterogeneity with OS and DFS/RFS.
Mucins phenotype | Covariates | Univariate analysis (OS) | Univariate analysis (DFS) | ||||
---|---|---|---|---|---|---|---|
Coefficient | SE | Coefficient | SE | ||||
MUC1 | Antibody | 0.055 | 0.087 | 0.538 | -0.142 | 0.882 | 0.883 |
Cut-off value | 0.0297 | 0.032 | 0.369 | 0.155 | 0.295 | 0.635 | |
TNM stage | 0.365 | 0.324 | 0.281 | 0.773 | 1.106 | 0.535 | |
Country | 0.048 | 0.462 | 0.323 | 0.155 | 0.295 | 0.635 | |
Year | -0.001 | 0.014 | 0.964 | -0.077 | 0.115 | 0.552 | |
MUC2 | Antibody | -0.204 | 0.215 | 0.367 | 0.550 | 0.252 | 0.094 |
Cut-off value | -0.027 | 0.043 | 0.552 | -0.030 | 0.221 | 0.898 | |
TNM stage | -0.309 | 0.124 | 0.054 | -0.270 | 0.838 | 0.763 | |
Country | 0.007 | 0.048 | 0.891 | 0.180 | 0.050 | 0.023 | |
Year | 0.036 | 0.030 | 0.264 | 0.108 | 0.030 | 0.022 | |
MUC5AC | Antibody | 0.464 | 0.269 | 0.135 | -0.139 | 0.434 | 0.769 |
Cut-off value | 0.187 | 0.158 | 0.282 | -0.248 | 0.193 | 0.288 | |
TNM stage | 0.923 | 0.211 | 0.055 | -0.652 | 0.961 | 0.546 | |
Country | 0.250 | 0.240 | 0.339 | -0.379 | 0.293 | 0.287 | |
Year | 0.135 | 0.073 | 0.859 | 0.102 | 0.069 | 0.236 |
In this meta-analysis, we assessed the association between MUC expression levels in CRC tissues and prognosis and investigate the associations between MUC expression levels and several CRC clinicopathological characteristics. Interestingly, findings demonstrated no association between combined MUC phenotype expression levels in CRC tissues and prognosis. However, in subgroup analyses stratified by MUC phenotype, a high level of MUC1 expression was associated with poor OS and DFS/RFS, a high level of MUC2 expression was associated with improved OS and DFS/RFS, and a high level of MUC5AC was associated with improved DFS/RFS. Generally, heterogeneity between studies was significantly reduced in the subgroup analyses stratified by MUC phenotype. Meanwhile, meta-regression analysis revealed that antibody for MUC, cut-off value for MUC, TNM stage, and histologic type were not significant sources of heterogeneity.
However, importantly, several studies have shown a correlation between MUC expression and patient with various cancers. For example, a meta-analysis reported that MUC expression was significantly higher in patients with esophageal adenocarcinoma than in normal squamous esophageal mucosa [
The current study explored the association between MUC expression levels in CRC tissues and CRC clinicopathological characteristics. A high level of MUC1 expression was associated with CRC in the rectum, deeper invasion, lymph node metastasis, distant metastasis, advanced tumor stage, and lymphatic invasion. Elevated MUC2 expression was associated with CRC in the colon, shallower lesions, negative lymph node metastasis, early stage of tumor, mucinous carcinoma, and larger tumor size. MUC5AC was more easily expressed in colon cancer. These findings implicate MUC1 in mechanisms that promote tumor invasion, lymph node metastasis, high stage, lymphatic invasion, and poor survival in CRC, while MUC2 may have a protective role. A number of studies have demonstrated a unique role for MUC in proliferation, survival, metastasis, epithelial-mesenchymal transition, and antiapoptosis in tumors [
Findings from the current meta-analysis indicate MUC1 may be a biomarker of poor prognosis in CRC and suggest that combined detection of MUC1 and MUC2 should be used to accurately predict CRC progression, metastasis, and treatment outcomes. Understanding the association between MUC expression levels and metastasis in CRC may help clarify the risk of metastasis at the time of diagnosis in patients with CRC, especially in those patients without symptoms or signs of metastasis. Clinically, MUC detection is simple and easy to implement.
This study was associated with several limitations. First, HRs from some of the included studies were calculated from Kaplan-Meier curves, which may have influenced the robustness of our findings. Second, the lack of a standardized detection methods and antibodies to detect MUC status may have affected the accuracy of our results. Third, despite the use of subgroup analysis and meta-regression to identify potential sources of heterogeneity between studies, they may have been additional sources of heterogeneity that impacted our findings. Finally, the sample size was small, and results should be considered preliminary.
In conclusion, findings from the current study suggest that MUC1 and MUC2 expression levels in CRC tissues are associated with OS, DFS/RFS, tumor site, depth of invasion, lymph node metastasis, distant metastasis, tumor stage, histologic type, and lymphatic invasion. These results indicate that MUC status can be used to differentiate between normal cells and CRC cells and predict a patient’s clinicopathological characteristics and prognosis. The clinical relevance of MUC regulation in CRC tissues remains to be elucidated in large well-designed cohort studies.
The authors declare that they have no conflicts of interest.
Chao Li is assigned to the data curation, investigation, methodology, resources, validation, and writing of the original draft. Didi Zuo is also assigned to the data curation, formal analysis, and investigation. Tao Liu is responsible for the formal analysis, investigation, and validation. Libin Yin is also responsible for the formal analysis and software. Chenyao Li is also assigned to software. Lei Wang is in charge of the conceptualization, funding acquisition, project administration, supervision, visualization, and writing of the review and editing.
Table S1: quality assessment of the included studies.