title: Tracking the molecular features of nonpolypoid colorectal neoplasms: a systematic review and meta-analysis.
abstract: OBJECTIVE
  Nonpolypoid colorectal neoplasms (NP-CRNs) are proposed as a major contributor to the occurrence of interval cancers, but their underlying biology remains controversial. We conducted a systematic review and meta-analysis to clarify the major biological events in NP-CRNs.
  
  
  METHODS
  We systematically searched for studies examining molecular characteristics of NP-CRNs. We performed random effect meta-analyses. We measured the heterogeneity among studies using I(2) and possible publication bias using funnel plots.
  
  
  RESULTS
  Fifty-three studies on KRAS, APC, or BRAF mutations, microsatellite instability (MSI), CpG island methylator phenotype (CIMP), or DNA promoter hypermethylation were included. We observed less KRAS mutations (summary odds ratio (OR) 0.30, confidence interval (CI)=0.19-0.46, I(2)=77.4%, CI=70.1-82.9) and APC mutations (summary OR 0.42, CI=0.24-0.72, I(2)=22.6%, CI=0.0-66.7) in NP-CRNs vs. protruded CRNs, whereas BRAF mutations were more frequent (summary OR 2.20, CI=1.01-4.81, I(2)=0%, CI=0-70.8), albeit all with large heterogeneity. Less KRAS mutations were especially found in NP-CRNs subtypes: depressed CRNs (summary OR 0.12, CI=0.05-0.29, I(2)=0%, CI=0-67.6), non-granular lateral spreading tumors (LSTs-NG) (summary OR 0.61, CI=0.37-1.0, I(2)=0%, CI=0-74.6), and early nonpolypoid carcinomas (summary OR 0.11, CI=0.06-0.19, I(2)=0%, CI=0-58.3). MSI frequency was similar in NP-CRNs and protruded CRNs (summary OR 0.99, CI=0.21-4.71, I(2)=70.3%, CI=38.4-85.7). Data for promoter hypermethylation and CIMP were inconsistent, precluding meaningful conclusions.
  
  
  CONCLUSIONS
  This meta-analysis provides indications that NP-CRNs are molecularly different from protruded CRNs. In particular, some subtypes of NP-CRNs, the depressed and LST-NG, are featured by less KRAS mutations than polypoid CRNs. Prospective, multicenter studies are needed to clarify the molecular pathways underlying nonpolypoid colorectal carcinogenesis and potential implications for surveillance intervals.
authors: Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands.
authors: Quirinus J M
authors: QJ
authors: Voorham
authors: Eveline J A
authors: EJ
authors: Rondagh
authors: Dirk L
authors: DL
authors: Knol
authors: Manon
authors: M
authors: van Engeland
authors: Beatriz
authors: B
authors: Carvalho
authors: Gerrit A
authors: GA
authors: Meijer
authors: Silvia
authors: S
authors: Sanduleanu
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics*; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D016001:Confidence Intervals; D018899:CpG Islands; D019175:DNA Methylation; D006801:Humans; D053842:Microsatellite Instability; D016017:Odds Ratio; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins / Q000235:genetics*
chemical_list: C555337:APC protein, human; D025601:Adenomatous Polyposis Coli Protein; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins