title: Expression of core clock genes in colorectal tumour cells compared with normal mucosa: a systematic review of clinical trials.
abstract: OBJECTIVE
  Experimental studies have shown that some circadian core clock genes may act as tumour suppressors and have an important role in the response to oncological treatment. This study investigated the evidence regarding modified expression of core clock genes in colorectal cancer and its correlation to clinicopathological features and survival.
  
  
  METHODS
  A systematic review was conducted without meta-analysis according to the PRISMA guidelines on 24 March 2014 using PubMed and EMBASE. Eligibility criteria were: study design, original research article, English language, human subjects and gene expression of colorectal cancer cells compared with healthy mucosa cells from specimens analysed by real-time or quantitative real-time polymer chain reaction. The expression of the core clock genes Period, Cryptochrome, Bmal1 and Clock in colorectal tumours were compared with healthy mucosa and correlated with clinicopathological features and survival.
  
  
  RESULTS
  Seventy-four articles were identified and 11 studies were included. Overall, gene expression of Period was significantly decreased in colorectal cancer cells compared with healthy mucosa cells. This tendency was also seen in the gene expression of Clock. Other core clock genes did not appear to be differentially expressed. Decreased Period gene expression was correlated to some clinicopathological features.
  
  
  CONCLUSIONS
  The Period genes seemed to be modified in colorectal tumour cells compared with normal mucosa. Core clock genes might be possible future biomarkers in colorectal cancer.
authors.affiliation: Centre for Perioperative Optimization, Department of Surgery, Herlev Hospital, University of Copenhagen, Herlev, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Fonnes
authors.forename: A M
authors.initials: AM
authors.lastname: Donatsky
authors.forename: I
authors.initials: I
authors.lastname: Gögenur
mesh_terms: D056930:ARNTL Transcription Factors / Q000235:genetics; D000230:Adenocarcinoma / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D056926:CLOCK Proteins / Q000235:genetics; D056925:Circadian Rhythm Signaling Peptides and Proteins / Q000235:genetics*; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D056931:Cryptochromes / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology; D056950:Period Circadian Proteins / Q000235:genetics; D011379:Prognosis
chemical_list: D056930:ARNTL Transcription Factors; D056925:Circadian Rhythm Signaling Peptides and Proteins; D056931:Cryptochromes; D056950:Period Circadian Proteins; D056926:CLOCK Proteins
keywords: Colorectal neoplasms; circadian clocks; gene expression