extracellular vesicles have a vast array of content composed of proteins , mrna , mirna , dna , lipids and transcriptional factors . the components are highly variable , functional , depend on cell origin , and exert powerful effects in recipient cells . remarkably , cancer cellderived ev contain functional oncogenic molecules , engendering a favorable microenvironment for cancer development . among the pathogenic components , numerous studies have shown that the evcontained mirna and proteins modulate surrounding cells , such as endothelial cells,17 fibroblasts18 and immune cells ( fig . 1).19 
  in 2007 , valadi et al.20 showed that variable rna , mrna and mirna can be transported between cells in ev . in 2010 , we and two other groups independently reported that ev mirna are transferred to recipient cells and translated into functional proteins.21 , 22 , 23 the vesiclerelated rna is called exosomal shuttle rna ( esrna ) . notably , it has been shown that esrna is poorly related to the rna from evproducing cells.24 , 25 , 26 this suggests that specific small rna are actively loaded into the ev . villarroyabeltri et al.27 report that sumoylated heterogeneous nuclear ribonucleoprotein a2b1 ( hnrnpa2b1 ) controls the sorting of mirna into ev through the recognition of specific sequence motifs . overall , the sort mechanisms are poorly understood and are likely to be associated with the mode of ev biogenesis . an increasing number of reports have shown that ev rna contribute to cancer development , such as cell proliferation,28 , 29 , 30 drug resistance,31 angiogenesis,17 immune modulation19 and premetastatic niche formation.32 
  the lipidbilayered ev can serve as suitable carriers for membrane proteins , allowing noncanonical cell  cell communication . the proteomic components of ev are specific , combining the common plasma membrane , cytosolic proteins and distinct celltype specific proteins.33 ev membrane proteins can also affect cells via ligandreceptor binding and activation . however , ev proteins , including cell adhesion proteins and enzymes , have a pivotal role in promoting cancer metastasis . in cancer patients , cancer cellderived ev represent elevated amounts of tumorspecific proteins in the blood.34 for instance , glioblastomaderived ev promote the propagation of malignancy through the transfer of epidermal growth factor receptor variant iii ( egfrviii ) , an oncogenic form of egfr.35 furthermore , luga et al.36 report that cancer associated fibroblasts secrete cd81enriched ev that promote breast cancer cell protrusive activity and motility via wntplanar cell polarity , which results in metastasis and cell migration . cancer cellderived ev also transfer pglycoproteins to induce drug resistance,37 transfer matrix metalloproteinases ( mmp ) to promote matrix degradation,38 and transfer natural killer group 2d ( nkg2d ) ligands to evade anticancer immune responses.39 these observations have been validated in numerous studies on the protein components of ev , and a few new initiatives are available online as free reference databases for ev investigators : exocarta ( http://www.exocarta.org),40 vesiclepedia ( microvesicles.org)41 and evpedia ( http://evpedia.info).42 
  the functional transfer of cancer pathogenic components in ev has been observed experimentally . cancer cells deliver their ev pathogenic components not only to their surrounding cells but also to distant cells , and these ev can modulate to prepare niches that support metastasis . therefore , therefore , there is an urgent need to develop predictive and early diagnostic markers for cancer metastasis and to clarify the molecular mechanisms of metastasis to develop effective treatment options . several studies , including ours , have reported that ev mediate the formation of premetastatic niches for the metastasis of various organs . ev components promote metastasis and transfer metastatic potential . furthermore , cancer cellderived ev push selected host tissues toward a premetastatic phenotype . jung et al.43 report that cd44v6enriched ev from pancreatic cancer cells promote premetastatic niche formation in lymph nodes and lung tissues . furthermore , they also found that these ev are rich in mir494 and mir5423p , which target cadherin17 and upregulate the mmp 2 and 9 transcription in premetastatic lung stroma cells.44 in renal cancer , grange et al.45 report that ev from cd105positive cancer stem cells stimulate angiogenesis and the formation of lung premetastatic niches . peinado et al.46 report that melanomaderived ev can determine the differentiation of bone marrow progenitor cells , resulting in the promotion of lung metastasis from melanoma cells . using serum from melanoma patients , they found that melanomaderived ev contain high tyrp2 , vla4 , hsp70 , met and rab27a proteins . these ev travel to the bone marrow , lungs and lymph nodes during metastasis and are involved in the preparation of tumor niches by altering the extracellular matrix , including tissue inflammation , increasing vascular permeability and promoting other proangiogenic events.47 finally , le et al.48 report that mir200containing ev promote breast cancer cell lung metastasis . transferring mir200 can alter gene expression and promote the met program for cancer cell colonization of distant tissues . in addition , they found that ev can promote metastasis and transform distal cells into metastatic cells . these data suggest that circulating ev from primary tumor developments and the formation of sites for metastasis may attract cancer cells to the niche , functioning as the first mediators of metastatic node formation.46 , 49 
  brain metastasis is also related to poor prognosis for cancer patients . one of the important events during brain metastasis is the destruction of the blood brain barrier ( bbb ) , which consists of the endothelium and surrounding cells.50 zhou et al.51 report that evmediated transfer of cancersecreted mir105 efficiently destroys tight junctions and the integrity of these natural barriers against metastasis . ev mir105 targets the tight junction protein zona occludens protein 1 ( zo1 ) and facilitates the migration of cancer cells to distant locations by disrupting tight junctions between endothelial cells , resulting in bbb breakdown . furthermore , increased expression of circulating ev mir105 can be detected during the premetastatic stage and correlated with the occurrence of metastasis in breast cancer patients . thus , the present study showed that ev mir105 destroys vascular endothelial barriers during early premetastatic niche formation and predicts metastasis in earlystage breast cancer patients . similarly , we have shown a novel mechanism for brain metastasis mediated by ev that triggers the destruction of the bbb.52 ev mir181c promotes breakdown of the bbb through abnormal localization of actin via the downregulation of its target 3phosphoinostidedependent protein kinase1 ( pdpk1 ) . pdpk1 degradation by mir181c leads to the downregulation of phosphorylated cofilin and the activated cofilininduced modulation of actin dynamics . moreover , serum levels of ev mir181c were significantly higher in the serum from brain metastasis breast cancer patients compared with the serum from nonbrain metastasis patients . in summary , these data suggest that ev influences the mechanisms of brain metastatic cancer . conversely , breast cancer patients often develop a recurrence years after resection of the primary tumor from cancer cells that have spread into metastatic niches , especially bone marrow . this was shown through the evidence that breast cancer cells survive for a long time in a dormant state . recently , we revealed that ev promote cancer cell dormancy through their mirna transfer in breast cancer.53 we found that the ev secreted by bone marrow mesenchymal stem cells ( bmmsc ) regulate the cancer dormancy state of metastatic breast cancer stem cells . we also clarified that ev mir23b from bmmsc suppresses the expression of marcks , which encodes a protein that promotes cell cycling and motility in a bone marrowmetastatic human breast cancer cell line . therefore , the bone marrow niche can release ev that deliver signals promoting metastatic cancer cell dormancy . both metastasis and recurrence are problematic issues delaying effective therapies for cancer treatments . understanding the pathophysiological role of circulating ev in blood may be a good target for cancer treatment.12 in general , ev reflect the physiological state of their original cells.3 cancer cellderived ev containing specific proteins and mirna are secreted into tumor microenvironments and circulation.12 , 54 ev have been isolated and characterized from different bodily fluids , such as serum , plasma , saliva , urine , ascites and breast milk.1 , 12 early detection of cancer is important to reduce mortality and improve survival . liquid biopsies using circulating ev can clarify tumor characteristics without obtaining an invasive biopsy of the tumor . currently , effort has been devoted to the utilization of ev as novel cancer diagnostic tools . importantly , mirna packaged in ev are intact in blood samples due to their resistance to rnases . this suggests the possibility of high reproducibility for this diagnostic approach.55 table 2 shows representative studies reporting dysregulated mirna in body fluidderived ev from patients , suggesting its potential as a diagnostic tool to enhance early cancer detection . extracellular vesicle ( ev ) mirna from body fluids of cancer patients as potential diagnostic markers cancer cellderived ev also contain tumorspecific proteins . recent proteomic studies have suggested that ev from cancer patients show specific protein profiles , thus indicating that the ev proteins might be useful for early detection of various cancers . melo et al.13 report crucial evidence on using the circulating ev protein glypican1 for diagnosis . using mass spectrum analyses positive circulating ev were detected in the serum of early pancreatic cancer patients with absolute specificity and sensitivity . the levels of glypican1 positive circulating ev correlated with tumor burden and the survival of presurgical and postsurgical patients . the data indicated that circulating ev proteins may serve as a potential noninvasive diagnostic and screening tool to detect cancers . currently , several promising cancer biomarkers have been found in patient body fluids and are summarized in table 3 . extracellular vesicle ( ev ) proteins from body fluids of cancer patients as potential diagnostic markers the identification and quantification of ev proteins in body fluids remain a major challenge compared with ev mirna because ev proteins are highly heterogeneous and are difficult to collect and handle.56 however , there have been no superior techniques to isolate ev with a small amount of human body fluid . furthermore , the ultracentrifugation normally used for ev isolation in basic research is unsuitable for most clinical settings . consequently , we have to develop highly sensitive and specific detection methods for analyzing ev proteins . currently , there have been various reports using specific antibodybased technologies for analyzing ev proteins from human body fluids without isolation . these methods consist of flow cytometry,57 protein microarray ( ev array),58 diagnostic magnetic resonance59 and nanoplasmonic sensing technology.60 despite these novel studies , the technological development of circulating ev detection is not yet mature . hurdles that these technologies have to overcome include low sample throughput , timeconsuming processes , and the variability and complexity of body fluids.61 
  in colon cancer , we have reported a sensitive and rapid analytical technology for profiling circulating ev proteins directly from colorectal cancer patient blood samples . yoshioka et al.14 showed that circulating ev ( cd147 and cd9 doublepositive ) can be used to detect colorectal cancer using  exoscreen . exoscreen can simply detect diseasespecific ev in the serum based on an amplified luminescent proximity homogeneous assay using photosensitizerbeads without an ev purification step . remarkably , we can detect circulating cancer cellderived ev by exoscreen in only 5 l serum from cancer patients . the receiveroperating characteristic curve indicated a diagnostic advent of cd147/cd9 doublepositive ev compared with conventional tumor antigen markers . therefore , exoscreen using specific ev antigens provides a new liquid biopsy technique for sensitively detecting diseasespecific ev.14 currently , it is clear that the intercellular communication of ev constitutes an exciting field . furthermore , many studies have strongly suggested great promises for ev transfer in cancer therapeutics and diagnostics . for tumor progression , ev pathogenic components , such as mirna and proteins , clearly function to establish premetastatic niches . in addition , ev biomarkers from easily obtainable body fluids , such as blood and urine , are suitable for clinical application . this novel detection technology without isolation processes will have an outstanding impact on future precision medicine for cancer patients . therefore , this is an attractive strategy for targeting cancer pathogenic components in ev with strong potential for cancer treatment ( fig . furthermore , they carry pathogenic components , such as mirna and proteins , which can mediate paracrine signaling in tumor microenvironments . circulating cancer in addition , circulating ev mirna and proteins have also been of interest as a source for liquid biopsy .
extracellular vesicles ( ev ) , known as exosomes and microvesicles , serve as versatile intercellular communication vehicles . increasing evidence has shown that cancer cellderived ev carry pathogenic components , such as proteins , messenger rna ( mrna ) , microrna ( mirna ) , dna , lipids and transcriptional factors , that can mediate paracrine signaling in the tumor microenvironment . 
 these data suggest that ev transfer of cancer pathogenic components enable longdistance crosstalk between cancer cells and distant organs , resulting in the promotion of the initial steps for premetastatic niche formation . understanding the metastatic mechanisms through ev 
 transfer may open up a new avenue for cancer therapeutic strategies . 
 furthermore , the circulating ev have also been of interest as a source for liquid biopsies . 
 ev in body fluids provide a reliable source of mirna and proteins for cancer biomarkers . 
 the tumorspecific components in ev effectively provide various messages on the physiological and pathological status of cancer patients . 
 although many researchers are searching for ev biomarkers using mirna microarrays and proteome analyses , the detection technology for circulating ev in body fluids has not yet reached the point of clinical application . in this review , 
 we summarize recent findings regarding ev function , specifically in metastasis through the transfer of cancer pathogenic components . 
 furthermore , we highlight the potential of using circulating ev for cancer diagnosis .