title: Metachronous colorectal cancer.
abstract: OBJECTIVE
  Although the diagnosis of metachronous colorectal cancer have increased, due primarily to improvements in diagnostic modalities, the potential risk factors for these tumours are not well known. We compared the characteristics of patients with metachronous and sporadic primary colorectal cancer to determine risk factors for its occurrence.
  
  
  METHODS
  We reviewed the records of 5447 patients with colorectal cancer, who had been treated at Asan Medical Centre between July 1989 and January 2004. A metachronous cancer was defined as a secondary colorectal cancer occurring more than 6 months after the index cancer.
  
  
  RESULTS
  Metachronous colorectal cancer occurred in 39 (0.7%) patients. Their average age was 53 years, somewhat younger than the average age of sporadic colorectal cancer patients (58 years). In patients with metachronous cancer, the cancer was more likely to be located in the right colon (P < 0.03), and the incidence of synchronous polyps or cancer was significantly higher (P < 0.001). The relative distributions of histological grades and clinicopathological characteristics were similar in index and metachronous cancers. Metachronous cancers were diagnosed more frequently at an early stage. The time interval between index and metachronous cancer ranged from 6 to 215 months (mean 39 months), with 13 (33.3%) patients diagnosed with metachronous cancer after 5 years.
  
  
  CONCLUSIONS
  We found that in patients aged < 50 years, existence of synchronous polyps or cancer influence on the development of metachronous colorectal cancer. Regular follow-up is necessary for early detection, even after 5 years, for these patients.
authors.affiliation: Colorectal Clinic, Department of Surgery, University of Ulsan College of Medicine and Asan Medical Centre, Seoul, Korea.
authors.forename: I J
authors.initials: IJ
authors.lastname: Park
authors.forename: C S
authors.initials: CS
authors.lastname: Yu
authors.forename: H C
authors.initials: HC
authors.lastname: Kim
authors.forename: Y H
authors.initials: YH
authors.lastname: Jung
authors.forename: K R
authors.initials: KR
authors.lastname: Han
authors.forename: J C
authors.initials: JC
authors.lastname: Kim
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D003111:Colonic Polyps / Q000473:pathology; D003113:Colonoscopy; D015179:Colorectal Neoplasms / Q000209:etiology* / Q000473:pathology* / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D016609:Neoplasms, Second Primary / Q000209:etiology* / Q000473:pathology* / Q000601:surgery; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors