Rectal DiseasesColonic DiseasesGingivitis, Necrotizing UlcerativeDiverticulosis, ColonicColorectal NeoplasmsAdenomaColonoscopyColorectal SurgeryColorectal Neoplasms, Hereditary NonpolyposisColonic PolypsRectal NeoplasmsColonic NeoplasmsAdenocarcinomaRectumSigmoidoscopyAdenomatous PolypsColonFluorouracilLiver NeoplasmsOrganoplatinum CompoundsLeucovorinTumor Markers, BiologicalNeoplasm StagingIntestinal PolypsAdenomatous Polyposis ColiPrognosisCarcinoembryonic AntigenMass ScreeningCamptothecinCarcinomaEarly Detection of CancerHT29 CellsCase-Control StudiesMicrosatellite RepeatsGene Expression Regulation, NeoplasticImmunohistochemistryMutS Homolog 2 ProteinNeoplasm MetastasisIntestinal MucosaColectomyHCT116 CellsGenes, APCRisk Factors