title: Familial colorectal cancer risk by subsite of primary cancer: a population-based study in Utah.
abstract: BACKGROUND
  Familial occurrence is common in colorectal cancer (CRC), but whether this increased familial risk differs by colonic subsite of the index patients CRC is not well understood.
  
  
  OBJECTIVE
  To quantify the risk of CRC in first-degree (FDR), second-degree (SDR) and first cousin (FC) relatives of individuals with CRC, stratified by subsite in the colorectum and age at diagnosis.
  
  
  METHODS
  Colorectal cancers diagnosed between 1980 and 2010 were identified from the Utah Cancer Registry and linked to pedigrees from the Utah Population Database. Age and gender-matched CRC-free controls were selected to form the comparison group for determining CRC risk in relatives using Cox regression analysis.
  
  
  RESULTS
  Of the 18,208 index patients diagnosed with CRC, 6584 (36.2%) were located in the proximal colon, 5986 (32.9%) in the distal colon and 5638 (31%) in the rectum. The elevated risk of CRC in relatives was similar in analysis stratified for CRC colorectal subsites in the index cases. FDR had similarly elevated risk of all site CRC, whether the index patient had cancer in the proximal colon [hazards ratio (HR): 1.85; 95% CI: 1.70-2.02], distal colon (HR: 1.90; 95% CI: 1.73-2.08) or rectum (HR: 1.83; 95% CI: 1.66-2.02) compared to relatives of controls. This risk was consistently greater for FDR when cases developed CRC below the age of 60 years.
  
  
  CONCLUSIONS
  Relatives of CRC patients have a similarly elevated risk of CRC regardless of colonic tumour subsite in the index patient, and it is greatest for relatives of younger age index cases.
authors.affiliation: Huntsman Cancer Institute, University of Utah, Salt Lake City, UT, USA; Department of Medicine (Gastroenterology), University of Utah, Salt Lake City, UT, USA.
authors.forename: N J
authors.initials: NJ
authors.lastname: Samadder
authors.forename: K R
authors.initials: KR
authors.lastname: Smith
authors.forename: G P
authors.initials: GP
authors.lastname: Mineau
authors.forename: R
authors.initials: R
authors.lastname: Pimentel
authors.forename: J
authors.initials: J
authors.lastname: Wong
authors.forename: K
authors.initials: K
authors.lastname: Boucher
authors.forename: L
authors.initials: L
authors.lastname: Pappas
authors.forename: H
authors.initials: H
authors.lastname: Singh
authors.forename: D
authors.initials: D
authors.lastname: Ahnen
authors.forename: R W
authors.initials: RW
authors.lastname: Burt
authors.forename: K
authors.initials: K
authors.lastname: Curtin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D003110:Colonic Neoplasms / Q000453:epidemiology* / Q000473:pathology; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000473:pathology; D005192:Family Health; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D012007:Rectum / Q000473:pathology*; D012189:Retrospective Studies; D012307:Risk Factors; D014589:Utah / Q000453:epidemiology; D055815:Young Adult