Exosomes　are　dish-shaped　phospholipid　bilayer-enclosed　membranous　vesicles　with　diameter　range　of　30-150　nm.　Exosomes　as　stable　vesicles　contain　various　bioactive　molecules　derived　from　the　cells　of　parental　origin,　including　proteins,　lipids,　DNA　fragments,　mRNAs,　miRNAs,　lncRNAs　etc.　Exosomes　are　secreted　by　almost　all　kinds　of　cells.　Here,　we　focus　on　the　application　of　exosomes　in　precision　oncology.　Nowadays,　accumulating　evidence　suggests　that　cancer　cells　release　the　excessive　amounts　of　exosomes　compared　to　normal　cells.　The　communications　through　exosomes　between　cancer　cells　and　cancer/normal　cells　could　make　the　exchange　of　genetic　information　and　reprogramming　of　the　recipient　cells.　Besides,　the　tumor-derived　exosomes　contribute　the　establishment　of　pre-metastatic　niche　and　distant　tissue　site　for　metastasis　of　cancer　cells.　That　may　leads　to　cancer　initiation,　progression,　metastasis　of　cancer　cells　and　escaping　from　immune　cell　surveillance.　In　this　review,　we　summarize　the　definition,　composition　and　the　potential　diagnostic/therapeutic　applications　of　exosomes.　We　introduce　that　there　are　several　kinds　of　proteins　enriched　in　exosomes　such　as　TSG101,　HSP70,　CD9　and　so　on,　which　could　be　as　the　biomarkers　to　monitor　the　qualification　and　purification　of　exosomes　we　purified,　in　which　play　a　pivotal　role　in　exosome　research.　We　describe　the　ways　of　recipient　cells　uptaking　exosomes　into　themselves　and　the　methods　of　exosome　purification.　Furthermore,　we　focus　on　non-invasive　liquid　biopsies　in　oncology,　relying　on　analyzing　material　including　molecules　as　well　as　whole　cells　that　are　found　in　bodily　fluids　such　as　blood　and　urine.　Liquid　biopsies　are　now　in　quick　development　and　have　been　being　an　intriguing　topic.　We　discuss　the　potential　role　of　circulating　tumor　cells,　circulating　tumor-derived　DNA/RNAs,　and　exosomes　in　liquid　biopsy　of　cancer.　We　discriminate　their　characteristics　and　focus　on　exosomes　that　are　used　in　liquid　biopsy.　Because　the　biomolecules　in　exosomes　are　derived　from　their　parental　cells,　these　contents　are　resembled　between　with　each　other.　On　this　basis,　it　is　conformed　that　they　can　reflect　the　dynamic　information　for　genetic　or　signaling　alteration　of　their　cells　of　origin.　We　also　highlighted　its　advanced　progression　in　cancer　diagnosis　and　therapeutic　targets.　It　has　been　assumed　that　their　contents　such　as　nucleotides　or　proteins　are　abnormally　enriched　in　tumor-derived　ones　compared　to　the　normal,　such　as　glypican-1　in　pancreatic　cancer　and　CD63　in　the　melanoma,　which　have　the　potential　to　be　diagnostic　biomarkers　in　cancers.　The　advanced　studies　have　shown　the　difference　between　exosomes　derived　from　tumor　cells　and　normal　cells,　which　may　mediate　different　signaling　pathways　of　the　recipient　cells.　These　facts　indicate　that　we　could　transform　exosomes　to　make　it　a　medium　to　mediate　agents　to　the　recipient　cells　or　a　tool　for　treatment.　For　example,　exosomes　can　serve　as　specific　delivery　vehicles　loaded　siRNAs/shRNAs　targeted　to　mRNAs,　proteins　or　small　molecules,　as　a　tool　of　gene　therapy.　We　also　point　out　that　we　are　still　in　early　step　of　understanding　the　nature　and　extent　of　the　involvement　of　exosomes　in　physiology　and　therapeutic　targets.　We　highlight　that　these　will　shed　light　on　the　new　strategy　for　cancer　diagnosis　and　therapy.　The　advanced　studies　in　exosomes　we　presented　may　make　greater　contribution　to　overcome　a　variety　of　cancer　in　the　era　of　precision　oncology.　©　2018,　Science　Press.　All　right　reserved.