title: Synchronous and Metachronous Colorectal Cancers: Distinct Disease Entities or Different Disease Courses?
abstract: OBJECTIVE
  This study aimed to investigate the clinicopathological characteristics of synchronous and metachronous colorectal cancers (CRCs).
  
  
  METHODS
  From January 1, 2001 to December 31, 2010, 5898 patients who underwent surgical resection for CRCs were enrolled. Synchronous CRC was defined as presence of more than one primary CRC within 6 months of resection of the primary tumor; while CRC that occurred at least 6 months later was regarded as metachronous CRC.
  
  
  RESULTS
  5346 patients were eligible for the study and divided into three groups: solitary, synchronous and metachronous CRC. The overall prevalence of the synchronous CRC was 2.2% and the 10-year cumulative incidence of metachronous cancer was 0.84%. 29 (64%) metachronous cancers were diagnosed within 3 years of the index cancer and the mean time interval was 3.2 years. Male gender and presence of associated adenoma were significant risk factors for both synchronous and metachronous CRC. Synchronous and metachronous CRC patients shared similar clinicopathological features except that the former were older than the latter by 3.7 years. The five-year survival rates were not different among the three groups.
  
  
  CONCLUSIONS
  Our study indicates that synchronous and metachronous CRC might represent similar disease entity with different courses.
authors.forename: Chih-Sheng
authors.initials: CS
authors.lastname: Huang
authors.forename: Shung-Haur
authors.initials: SH
authors.lastname: Yang
authors.forename: Chun-Chi
authors.initials: CC
authors.lastname: Lin
authors.forename: Yuan-Tsiu
authors.initials: YT
authors.lastname: Lan
authors.forename: Shin-Ching
authors.initials: SC
authors.lastname: Chang
authors.forename: Huann-Sheng
authors.initials: HS
authors.lastname: Wang
authors.forename: Wei-Shone
authors.initials: WS
authors.lastname: Chen
authors.forename: Tzu-Chen
authors.initials: TC
authors.lastname: Lin
authors.forename: Jen-Kou
authors.initials: JK
authors.lastname: Lin
authors.forename: Jeng-Kai
authors.initials: JK
authors.lastname: Jiang
mesh_terms: D000230:Adenocarcinoma / Q000401:mortality / Q000473:pathology*; D000236:Adenoma / Q000473:pathology*; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000401:mortality / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009378:Neoplasms, Multiple Primary / Q000401:mortality / Q000473:pathology*; D016609:Neoplasms, Second Primary / Q000401:mortality / Q000473:pathology*; D012189:Retrospective Studies; D012737:Sex Factors; D015996:Survival Rate