title: [Population screening for colorectal cancer: a systematic review].
abstract: BACKGROUND
  Colorectal cancer (CRC) is a serious public health problem due to its high frequency and the mortality it provokes. This disease presents a series of characteristics that make it an ideal candidate for population screening. The aim of the present study was to analyze current knowledge on the efficacy/effectiveness of CRC screening through the fecal occult blood test (FOBT), rectosigmoidoscopy and colonoscopy in individuals without symptoms of this disease.
  
  
  METHODS
  We performed a systematic review of the literature on each of the methods of early detection. The databases consulted were MEDLINE and PREMEDLINE (1966-2002), Embase (1980-2002), HTA and Cochrane, among others. Articles were selected using explicit criteria and were classified according to their level of scientific evidence.
  
  
  RESULTS
  The best validated test is the FOBT, with the greatest number of randomized controlled trials. The results on the sensitivity and specificity of this test and reduction in mortality from CRC varied widely, depending on the technique used. The decrease in mortality from CRC in groups that underwent screening through FOBT was between 15% and 33%. The number and quality of the studies performed to evaluate flexible sigmoidoscopy and colonoscopy as methods of early detection were much lower. Although the rate of detection of polyps is greater than with the FOBT, the value of these tests as screening techniques has not been analyzed through randomized controlled trials.
  
  
  CONCLUSIONS
  Population screening for CRC reduces mortality from this disease. However, consensus is lacking on the screening method of choice and on the frequency with which screening should be performed. The method best supported by the evidence as a primary detection test is the FOBT. To date, sigmoidoscopy and colonoscopy should be used as diagnostic tests only, mainly because of their invasiveness.
authors.affiliation: Axencia de Avaliación de Tecnoloxías Sanitarias de Galicia (avalia-t), Subdirección Xeral de Planificación Sanitaria e Aseguramento, Servicio Galego de Saúde, Santiago de Compostela, A Coruña, Spain. lucinda.paz.valinas@sergas.es
authors.forename: L
authors.initials: L
authors.lastname: Paz-Valiñas
authors.forename: G
authors.initials: G
authors.lastname: Atienza Merino
mesh_terms: D002986:Clinical Trials as Topic; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000401:mortality; D006801:Humans; D008403:Mass Screening / Q000379:methods*; D009780:Occult Blood; D012812:Sigmoidoscopy
vernacular_title: Cribado poblacional del cáncer colorrectal: una revisión sistemática.