What Is Cancer? - NCI

Differences between Cancer Cells and Normal Cells Skiptomaincontent Español 1-800-4-CANCER LiveChat Publications Dictionary Home AboutCancer UnderstandingCancer UnderstandingCancer WhatIsCancer? CancerStatistics CancerDisparities WhatIsCancer? GetemailupdatesfromNCIoncancerhealthinformation,news,andothertopics GetemailupdatesfromNCI Adividingbreastcancercell. Credit:NationalCancerInstitute/Univ.ofPittsburghCancerInstitute TheDefinitionofCancer Cancerisadiseaseinwhichsomeofthebody’scellsgrowuncontrollablyandspreadtootherpartsofthebody.  Cancercanstartalmostanywhereinthehumanbody,whichismadeupoftrillionsofcells.Normally,humancellsgrowandmultiply(throughaprocesscalledcelldivision)toformnewcellsasthebodyneedsthem.Whencellsgrowoldorbecomedamaged,theydie,andnewcellstaketheirplace. Sometimesthisorderlyprocessbreaksdown,andabnormalordamagedcellsgrowandmultiplywhentheyshouldn’t.Thesecellsmayformtumors,whicharelumpsoftissue.Tumorscanbecancerousornotcancerous(benign).  Canceroustumorsspreadinto,orinvade,nearbytissuesandcantraveltodistantplacesinthebodytoformnewtumors(aprocesscalledmetastasis).Canceroustumorsmayalsobecalledmalignanttumors.Manycancersformsolidtumors,butcancersoftheblood,suchasleukemias,generallydonot. Benigntumorsdonotspreadinto,orinvade,nearbytissues.Whenremoved,benigntumorsusuallydon’tgrowback,whereascanceroustumorssometimesdo.Benigntumorscansometimesbequitelarge,however.Somecancauseserioussymptomsorbelifethreatening,suchasbenigntumorsinthebrain. DifferencesbetweenCancerCellsandNormalCells Cancercellsdifferfromnormalcellsinmanyways.Forinstance,cancercells: growintheabsenceofsignalstellingthemtogrow.Normalcellsonlygrowwhentheyreceivesuchsignals.  ignoresignalsthatnormallytellcellstostopdividingortodie(aprocessknownasprogrammedcelldeath,orapoptosis). invadeintonearbyareasandspreadtootherareasofthebody.Normalcellsstopgrowingwhentheyencounterothercells,andmostnormalcellsdonotmovearoundthebody.  tellbloodvesselstogrowtowardtumors. Thesebloodvesselssupplytumorswithoxygenandnutrientsandremovewasteproductsfromtumors. hidefromtheimmunesystem.Theimmunesystemnormallyeliminatesdamagedorabnormalcells.  tricktheimmunesystemintohelpingcancercellsstayaliveandgrow.Forinstance,somecancercellsconvinceimmunecellstoprotectthetumorinsteadofattackingit. accumulatemultiplechangesintheirchromosomes,suchasduplicationsanddeletionsofchromosomeparts.Somecancercellshavedoublethenormalnumberofchromosomes. relyondifferentkindsofnutrientsthannormalcells.Inaddition,somecancercellsmakeenergyfromnutrientsinadifferentwaythanmostnormalcells.Thisletscancercellsgrowmorequickly.  Manytimes,cancercellsrelysoheavilyontheseabnormalbehaviorsthattheycan’tsurvivewithoutthem.Researchershavetakenadvantageofthisfact,developingtherapiesthattargettheabnormalfeaturesofcancercells.Forexample,somecancertherapiespreventbloodvesselsfromgrowingtowardtumors,essentiallystarvingthetumorofneedednutrients.  HowDoesCancerDevelop? Enlarge Canceriscausedbycertainchangestogenes,thebasicphysicalunitsofinheritance.GenesarearrangedinlongstrandsoftightlypackedDNAcalledchromosomes. Credit:TereseWinslow Cancerisageneticdisease—thatis,itiscausedbychangestogenesthatcontrolthewayourcellsfunction,especiallyhowtheygrowanddivide. Geneticchangesthatcausecancercanhappenbecause: oferrorsthatoccurascellsdivide.  ofdamagetoDNAcausedbyharmfulsubstancesintheenvironment,suchasthechemicalsintobaccosmokeandultravioletraysfromthesun.(OurCancerCausesandPreventionsectionhasmoreinformation.)  theywereinheritedfromourparents.  ThebodynormallyeliminatescellswithdamagedDNAbeforetheyturncancerous.Butthebody’sabilitytodosogoesdownasweage.Thisispartofthereasonwhythereisahigherriskofcancerlaterinlife. Eachperson’scancerhasauniquecombinationofgeneticchanges.Asthecancercontinuestogrow,additionalchangeswilloccur.Evenwithinthesametumor,differentcellsmayhavedifferentgeneticchanges. FundamentalsofCancer Cancerisadiseasecausedwhencellsdivideuncontrollablyandspreadintosurroundingtissues. CanceriscausedbychangestoDNA.Mostcancer-causingDNAchangesoccurinsectionsofDNAcalledgenes.Thesechangesarealsocalledgeneticchanges. ADNAchangecancausegenesinvolvedinnormalcellgrowthtobecomeoncogenes.Unlikenormalgenes,oncogenescannotbeturnedoff,sotheycauseuncontrolledcellgrowth.  Innormalcells,tumorsuppressorgenespreventcancerbyslowingorstoppingcellgrowth.DNAchangesthatinactivatetumorsuppressorgenescanleadtouncontrolledcellgrowthandcancer. Withinatumor,cancercellsaresurroundedbyavarietyofimmunecells,fibroblasts,molecules,andbloodvessels—what’sknownasthetumormicroenvironment.Cancercellscanchangethemicroenvironment,whichinturncanaffecthowcancergrowsandspreads. Immunesystemcellscandetectandattackcancercells.Butsomecancercellscanavoiddetectionorthwartanattack.Somecancertreatmentscanhelptheimmunesystembetterdetectandkillcancercells. Eachperson’scancerhasauniquecombinationofgeneticchanges.Specificgeneticchangesmaymakeaperson’scancermoreorlesslikelytorespondtocertaintreatments. Geneticchangesthatcausecancercanbeinheritedorarisefromcertainenvironmentalexposures.Geneticchangescanalsohappenbecauseoferrorsthatoccurascellsdivide. Mostoften,cancer-causinggeneticchangesaccumulateslowlyasapersonages,leadingtoahigherriskofcancerlaterinlife. Cancercellscanbreakawayfromtheoriginaltumorandtravelthroughthebloodorlymphsystemtodistantlocationsinthebody,wheretheyexitthevesselstoformadditionaltumors.Thisiscalledmetastasis. TypesofGenesthatCauseCancer Thegeneticchangesthatcontributetocancertendtoaffectthreemaintypesofgenes—proto-oncogenes,tumorsuppressorgenes,andDNArepairgenes.Thesechangesaresometimescalled“drivers”ofcancer. Proto-oncogenesareinvolvedinnormalcellgrowthanddivision.However,whenthesegenesarealteredincertainwaysoraremoreactivethannormal,theymaybecomecancer-causinggenes(oroncogenes),allowingcellstogrowandsurvivewhentheyshouldnot. Tumorsuppressorgenesarealsoinvolvedincontrollingcellgrowthanddivision.Cellswithcertainalterationsintumorsuppressorgenesmaydivideinanuncontrolledmanner. DNArepairgenesareinvolvedinfixingdamagedDNA.Cellswithmutationsinthesegenestendtodevelopadditionalmutationsinothergenesandchangesintheirchromosomes,suchasduplicationsanddeletionsofchromosomeparts.Together,thesemutationsmaycausethecellstobecomecancerous. Asscientistshavelearnedmoreaboutthemolecularchangesthatleadtocancer,theyhavefoundthatcertainmutationscommonlyoccurinmanytypesofcancer. Nowtherearemanycancertreatmentsavailablethattargetgenemutationsfoundincancer.Afewofthesetreatmentscanbeusedbyanyonewithacancerthathasthetargetedmutation,nomatterwherethecancerstartedgrowing. WhenCancerSpreads Enlarge Inmetastasis,cancercellsbreakawayfromwheretheyfirstformedandformnewtumorsinotherpartsofthebody.  Credit:NationalCancerInstitute/TereseWinslow Acancerthathasspreadfromtheplacewhereitfirstformedtoanotherplaceinthebodyiscalledmetastaticcancer.Theprocessbywhichcancercellsspreadtootherpartsofthebodyiscalledmetastasis. Metastaticcancerhasthesamenameandthesametypeofcancercellsastheoriginal,orprimary,cancer.Forexample,breastcancerthat formsametastatictumorinthelungismetastaticbreastcancer,notlungcancer. Underamicroscope,metastaticcancercellsgenerallylookthesameascellsoftheoriginalcancer.Moreover,metastaticcancercellsandcellsoftheoriginalcancerusuallyhavesomemolecularfeaturesincommon,suchasthepresenceofspecificchromosomechanges. Insomecases,treatmentmayhelpprolongthelivesofpeoplewithmetastaticcancer.Inothercases,theprimarygoaloftreatment formetastaticcanceristocontrolthegrowthofthecancerortorelievesymptomsitiscausing.Metastatictumorscancauseseveredamagetohowthebodyfunctions,andmostpeoplewhodieofcancerdieofmetastaticdisease.  TissueChangesthatAreNotCancer Noteverychangeinthebody’stissuesiscancer.Sometissuechangesmaydevelopintocanceriftheyarenottreated,however.Herearesomeexamplesoftissuechangesthatarenotcancerbut,insomecases,aremonitoredbecausetheycouldbecomecancer: Hyperplasiaoccurswhencellswithinatissuemultiplyfasterthannormalandextracellsbuildup.However,thecellsandthewaythetissueisorganizedstilllooknormalunderamicroscope.Hyperplasiacanbecausedbyseveralfactorsorconditions,includingchronicirritation. Dysplasiaisamoreadvancedconditionthanhyperplasia.Indysplasia,thereisalsoabuildupofextracells.Butthecellslookabnormalandtherearechangesinhowthetissueisorganized.Ingeneral,themoreabnormalthecellsandtissuelook,thegreaterthechancethatcancerwillform.Sometypesofdysplasiamayneedtobemonitoredortreated,butothersdonot.Anexampleofdysplasiaisanabnormalmole(calledadysplasticnevus)thatformsontheskin.Adysplasticnevuscanturnintomelanoma,althoughmostdonot. Carcinomainsitu isanevenmoreadvancedcondition.Althoughitissometimescalledstage0cancer, itisnotcancerbecausetheabnormalcellsdonotinvadenearbytissuethewaythatcancercellsdo.Butbecausesomecarcinomasinsitumaybecomecancer,theyareusuallytreated. Normalcellsmaybecomecancercells.Beforecancercellsformintissuesofthebody,thecellsgothroughabnormalchangescalledhyperplasiaanddysplasia.Inhyperplasia,thereisanincreaseinthenumberofcellsinanorganortissuethatappearnormalunderamicroscope.Indysplasia,thecellslookabnormalunderamicroscopebutarenotcancer.Hyperplasiaanddysplasiamayormaynotbecomecancer. Credit:TereseWinslow TypesofCancer Therearemorethan100typesofcancer.Typesofcancerareusuallynamedfortheorgansortissueswherethecancersform.Forexample,lungcancerstartsinthelung,andbraincancerstartsinthebrain.Cancersalsomaybedescribedbythetypeofcellthatformedthem,suchasanepithelialcellorasquamouscell. YoucansearchNCI’swebsiteforinformationonspecifictypesofcancerbasedonthecancer’slocationinthebodyorbyusingourAtoZListofCancers.Wealsohaveinformationonchildhoodcancersandcancersinadolescentsandyoungadults. Herearesomecategoriesofcancersthatbegininspecifictypesofcells: Carcinoma Carcinomasarethemostcommontypeofcancer.Theyareformedbyepithelialcells,whicharethecellsthatcovertheinsideandoutsidesurfacesofthebody.Therearemanytypesofepithelialcells,whichoftenhaveacolumn-likeshapewhenviewedunderamicroscope. Carcinomasthatbeginindifferentepithelialcelltypeshavespecificnames: Adenocarcinomaisacancerthatformsinepithelialcellsthatproducefluidsormucus.Tissueswiththistypeofepithelialcellaresometimescalledglandulartissues.Mostcancersofthebreast,colon,andprostateareadenocarcinomas. Basalcellcarcinomaisacancerthatbeginsinthelowerorbasal(base)layeroftheepidermis,whichisaperson’souterlayerofskin. Squamouscellcarcinomaisacancerthatformsinsquamouscells,whichareepithelialcellsthatliejustbeneaththeoutersurfaceoftheskin.Squamouscellsalsolinemanyotherorgans,includingthestomach,intestines,lungs,bladder,andkidneys.Squamouscellslookflat,likefishscales,whenviewedunderamicroscope.Squamouscellcarcinomasaresometimescalledepidermoidcarcinomas. Transitionalcellcarcinomaisacancerthatformsinatypeofepithelialtissuecalledtransitionalepithelium,orurothelium.Thistissue,whichismadeupofmanylayersofepithelialcellsthatcangetbiggerandsmaller,isfoundintheliningsofthebladder,ureters,andpartofthekidneys(renalpelvis),andafewotherorgans.Somecancersofthebladder,ureters,andkidneysaretransitionalcellcarcinomas. Sarcoma Enlarge Softtissuesarcomaformsinsofttissuesofthebody,includingmuscle,tendons,fat,bloodvessels,lymphvessels,nerves,andtissuearoundjoints. Credit:TereseWinslow Sarcomasarecancersthatforminboneandsofttissues,includingmuscle,fat,bloodvessels,lymphvessels,andfibroustissue(suchastendonsandligaments). Osteosarcomaisthemostcommoncancerofbone.Themostcommontypesofsofttissuesarcomaareleiomyosarcoma,Kaposisarcoma,malignantfibroushistiocytoma,liposarcoma,anddermatofibrosarcomaprotuberans. Ourpageonsofttissuesarcomahasmoreinformation. Leukemia Cancersthatbeginintheblood-formingtissueofthebonemarrowarecalledleukemias.Thesecancersdonotformsolidtumors.Instead,largenumbersofabnormalwhitebloodcells(leukemiacellsandleukemicblastcells)buildupinthebloodandbonemarrow,crowdingoutnormalbloodcells.Thelowlevelofnormalbloodcellscanmakeitharderforthebodytogetoxygentoitstissues,controlbleeding,orfightinfections.  Therearefourcommontypesofleukemia,whicharegroupedbasedonhowquicklythediseasegetsworse(acuteorchronic)andonthetypeofbloodcellthecancerstartsin(lymphoblasticormyeloid).Acuteformsofleukemiagrowquicklyandchronicformsgrowmoreslowly. Ourpageonleukemiahasmoreinformation. Lymphoma Lymphomaiscancerthatbeginsinlymphocytes(TcellsorBcells).Thesearedisease-fightingwhitebloodcellsthatarepartoftheimmunesystem.Inlymphoma,abnormallymphocytesbuildupinlymphnodesandlymphvessels,aswellasinotherorgansofthebody. Therearetwomaintypesoflymphoma: Hodgkinlymphoma–PeoplewiththisdiseasehaveabnormallymphocytesthatarecalledReed-Sternbergcells.ThesecellsusuallyformfromBcells. Non-Hodgkinlymphoma–Thisisalargegroupofcancersthatstartinlymphocytes.ThecancerscangrowquicklyorslowlyandcanformfromBcellsorTcells. Ourpageonlymphomahasmoreinformation. MultipleMyeloma Multiplemyelomaiscancerthatbeginsinplasmacells,anothertypeofimmunecell.Theabnormalplasmacells,calledmyelomacells,buildupinthebonemarrowandformtumorsinbonesallthroughthebody.MultiplemyelomaisalsocalledplasmacellmyelomaandKahlerdisease. Ourpageonmultiplemyelomaandotherplasmacellneoplasmshasmoreinformation. Melanoma Melanomaiscancerthatbeginsincellsthatbecomemelanocytes,whicharespecializedcellsthatmakemelanin(thepigmentthatgivesskinitscolor).Mostmelanomasformontheskin,butmelanomascanalsoforminotherpigmentedtissues,suchastheeye. Ourpagesonskincancerandintraocularmelanomahavemoreinformation. BrainandSpinalCordTumors Therearedifferenttypesofbrainandspinalcordtumors.Thesetumorsarenamedbasedonthetypeofcellinwhichtheyformedandwherethetumorfirstformedinthecentralnervoussystem.Forexample,anastrocytictumorbeginsinstar-shapedbraincellscalledastrocytes,whichhelpkeepnervecellshealthy.Braintumorscanbebenign(notcancer)ormalignant(cancer). Ourpagesonbrainandspinalcordtumorsinadults and brainandspinalcordtumorsinchildren havemoreinformation. OtherTypesofTumors GermCellTumors Germcelltumorsareatypeoftumorthatbeginsinthecellsthatgiverisetospermoreggs.Thesetumorscanoccuralmostanywhereinthebodyandcanbeeitherbenignormalignant. Ourpageofcancersbybodylocation/systemincludesalistofgermcelltumorswithlinkstomoreinformation. NeuroendocrineTumors Neuroendocrinetumorsformfromcellsthatreleasehormonesintothebloodinresponsetoasignalfromthenervoussystem.Thesetumors,whichmaymakehigher-than-normalamountsofhormones,cancausemanydifferentsymptoms.Neuroendocrinetumorsmaybebenignormalignant. Ourdefinitionofneuroendocrinetumorshasmoreinformation. CarcinoidTumors Carcinoidtumorsareatypeofneuroendocrinetumor.Theyareslow-growingtumorsthatareusuallyfoundinthegastrointestinalsystem(mostoftenintherectumandsmallintestine).Carcinoidtumorsmayspreadtotheliverorothersitesinthebody,andtheymaysecretesubstancessuchasserotoninorprostaglandins,causingcarcinoidsyndrome. Ourpageongastrointestinalcarcinoidtumorshasmoreinformation.