**2. The variety of extracellular vesicles**

Replacing EVs includes a heterogeneous population of membrane vesicles categorized depending on the mechanism by which they are released from cells. According to their size and mechanisms of biogenesis, EVs can be categorized into three classes: (a) exosomes, (b) ectosomes or shedding microvesicles, and (c) apoptotic bodies [17, 18]. Differentiation criteria are based on their size, content, and by a certain combination of markers (**Figure 1** and **Table 1**). Cancerous cells have been described to release exosomes and ectosomes and some other additional subpopulations of EVs [19].

#### **2.1 Exosomes**

Exosomes are EVs with multivesicular endosomal origin released by all cell types [33]. Exosomes are found in physiological fluids such as blood and plasma [34, 35], urine [36], cerebral fluid [37], saliva [38, 39], seminal fluid [40], breast milk [41, 42], and amniotic fluid [43, 44]. The presence of EVs has been reported in interstitial spaces since they are released by B cells [45], T cells [46], dendritic cells [47], platelets [48], Schwann cells [49], tumor cells [50], cardiomyocytes [51], endothelial cells [52], stem cells [50], and telocytes [53–55]. Exosomes are able to influence cells from the local environment and also distant target cells, thus regulating intercellular signaling [56]. Their size varies between 30 and 100 nm, and as membrane vesicles, they are delineated by a specific lipid bilayer similar to that of the cells they originate from [57]. Studies have shown that while normal human blood contains about 2000 trillion exosomes, the blood of cancer patients contains a double amount, about 4000 trillion exosomes [57]. In noncancerous cells, exosome secretion was suggested to play a role in cellular homeostasis by removing harmful cytoplasmic DNA of normal cells and in preventing viral hijacking of host cells by excreting viral DNA from cells as shown by Takahashi et al. [58].

The plasma of cancer patients contains different types of exosomes, some released by normal cells and others released by cancerous cells, explaining the heterogeneity in size (30–150 nm) of the exosomal population [59]. Exosomes can be isolated from cancer patients' plasma with a variety of methods [60]. They are based not only on classical techniques such as ultracentrifugation, but also on some modern ones such as size exclusion chromatography [61].

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**2.2 Ectosomes**

**Figure 1.**

somes had its peak in 2012 [20, 63].

*Extracellular Vesicles in Cancer*

*DOI: http://dx.doi.org/10.5772/intechopen.85117*

Tumor cell-derived exosomes are able to promote inflammation and are able to compromise innate immunity by delivering different signals, which affect the proliferation, apoptosis, cytokine production, and reprogramming of T cells [62].

*Classification of EVs based on their diameter (expressed in nm) (A) or on their mechanism of biogenesis (B).*

Ectosomes are a heterogeneous vesicle population, ranging in diameter between

100 and 1000 nm. Discovered in approximately the same time as exosomes, in 1990s, ectosomes did not attract the same interest as the study of exosomes. While the interest in exosomes reached the maximum between 2008 and 2010, the ecto-

Ectosomes are known under different names, which might be misleading (**Table 1**), while ecto is a prefix that means outwardly, externally, and is therefore suggestive of their way of forming. The mechanism of formation of ectosomes differs greatly from that of exosomes, as well as their cargo molecules. Ectosome formation does not require exocytosis. Ectosomes are formed by direct outward

*Extracellular Vesicles and Their Importance in Human Health*

and melanoma [14–16].

subpopulations of EVs [19].

**2.1 Exosomes**

**2. The variety of extracellular vesicles**

provided some criteria to classify EVs into three groups: microvesicles (MVs), exosomes, and apoptotic bodies (for details visit www.isev.org). These vesicles are secreted by both normal cells and cancerous cells as means of cell-to-cell communication. Alternatively, they may be prepared artificially from the engineered artificial lipid vesicles called liposomes in which EVs' features, components, or cargos are

EVs are actively involved in cell-to-cell communication, inflammation, chronic disease development and progression, pre-metastatic niche formation, and the metastatic organotropism of different tumor types [8]. Tumor-derived EVs (TEVs) have been reported to play major roles in the onset, progression, and metastasis of cancer, including ovarian [9], breast [10], colorectal [11, 12], prostate cancer [13],

Here, we review knowledge about EVs in cancer, with a focus on breast and ovarian cancers. We discuss the importance of the content of EVs (e.g., nucleic acids,

Replacing EVs includes a heterogeneous population of membrane vesicles categorized depending on the mechanism by which they are released from cells. According to their size and mechanisms of biogenesis, EVs can be categorized into three classes: (a) exosomes, (b) ectosomes or shedding microvesicles, and (c) apoptotic bodies [17, 18]. Differentiation criteria are based on their size, content, and by a certain combination of markers (**Figure 1** and **Table 1**). Cancerous cells have been described to release exosomes and ectosomes and some other additional

Exosomes are EVs with multivesicular endosomal origin released by all cell types [33]. Exosomes are found in physiological fluids such as blood and plasma [34, 35], urine [36], cerebral fluid [37], saliva [38, 39], seminal fluid [40], breast milk [41, 42], and amniotic fluid [43, 44]. The presence of EVs has been reported in interstitial spaces since they are released by B cells [45], T cells [46], dendritic cells [47], platelets [48], Schwann cells [49], tumor cells [50], cardiomyocytes [51], endothelial cells [52], stem cells [50], and telocytes [53–55]. Exosomes are able to influence cells from the local environment and also distant target cells, thus regulating intercellular signaling [56]. Their size varies between 30 and 100 nm, and as membrane vesicles, they are delineated by a specific lipid bilayer similar to that of the cells they originate from [57]. Studies have shown that while normal human blood contains about 2000 trillion exosomes, the blood of cancer patients contains a double amount, about 4000 trillion exosomes [57]. In noncancerous cells, exosome secretion was suggested to play a role in cellular homeostasis by removing harmful cytoplasmic DNA of normal cells and in preventing viral hijacking of host cells by

excreting viral DNA from cells as shown by Takahashi et al. [58].

modern ones such as size exclusion chromatography [61].

The plasma of cancer patients contains different types of exosomes, some released by normal cells and others released by cancerous cells, explaining the heterogeneity in size (30–150 nm) of the exosomal population [59]. Exosomes can be isolated from cancer patients' plasma with a variety of methods [60]. They are based not only on classical techniques such as ultracentrifugation, but also on some

incorporated and are the most likely to be useful for drug delivery [7].

and proteins) in cancer development, metastasis, and drug resistance.

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#### **Figure 1.**

*Classification of EVs based on their diameter (expressed in nm) (A) or on their mechanism of biogenesis (B).*

Tumor cell-derived exosomes are able to promote inflammation and are able to compromise innate immunity by delivering different signals, which affect the proliferation, apoptosis, cytokine production, and reprogramming of T cells [62].

#### **2.2 Ectosomes**

Ectosomes are a heterogeneous vesicle population, ranging in diameter between 100 and 1000 nm. Discovered in approximately the same time as exosomes, in 1990s, ectosomes did not attract the same interest as the study of exosomes. While the interest in exosomes reached the maximum between 2008 and 2010, the ectosomes had its peak in 2012 [20, 63].

Ectosomes are known under different names, which might be misleading (**Table 1**), while ecto is a prefix that means outwardly, externally, and is therefore suggestive of their way of forming. The mechanism of formation of ectosomes differs greatly from that of exosomes, as well as their cargo molecules. Ectosome formation does not require exocytosis. Ectosomes are formed by direct outward


#### **Table 1.**

*Classification of EVs based on size and their biogenesis.*

budding of the plasma membrane in specialized microdomains of the plasmalemma, the phenomenon known as microvesicle shedding [29]. They are released both by cells in normal resting state and by cells upon stimulation. Ectosome fusion with the plasma membrane of a recipient cell is followed by changes in antigens, enzymes, and other proteins in a specific site of plasmalemma, while their content release into the cytoplasm can alter the recipients' cell gene expression [64, 65]. Tumor-derived ectosomes were shown to have immunosuppressive properties by inducing the chemotaxis of granulocytes, lymphocytes, and monocytes due to several chemokines (e.g., particularly IL-8) transported in ectosomes [66].

Oncosomes are a particular type of ectosomes, excessively large, which can even reach 1000 nm, characteristic to advanced cancers. There is a confusion in the use of these terms in the literature and that is why we thought to treat oncosomes as a particular category of ectosomes. The generic name of ectosomes can include oncosomes, while the name of oncosomes excludes ectosomes released from normal cells. Oncosomes content is adapted to serve cancer metabolism, so they will contain enzymes involved in glucose, glutamine, and amino acid metabolism. Furthermore, oncosomes are enriched in proteins, which have a

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**3.1 Nucleic acids**

*Extracellular Vesicles in Cancer*

detection of cancer [67].

**2.3 Apoptotic bodies**

*DOI: http://dx.doi.org/10.5772/intechopen.85117*

be divided into specific subclasses [70].

role in cell migration, angiogenesis, and cancer progression and metastasis [28]. Oncosomes allow intercellular transfer of oncogenes, hence the motivation to be considered as existing biomarkers in the blood or plasma of patients for the

Apoptotic bodies (ApoBDs) are the largest type of extracellular vesicles (typically 1–5μm in diameter) visible during an apoptotic process. Kerr in 1972 proposed the term "apoptotic body" [68]. ApoBDs are released as blebs of cells undergoing apoptosis and consist of cytoplasm, organelles with or without a nuclear fragment. It has also been shown that ApoBDs can harbor proteins, lipids, DNA, rRNA, organelles, and cytosol [18]; this is the reason why the disassembly of an apoptotic cell into ApoBDs can mediate intercellular communication and may contribute to the development of various disease states [69]. These bodies are then phagocytosed by macrophages or neoplastic cells and degraded within phagolysosomes. Their formation has been proposed to play an important role in the clearance of apoptotic cells by phagocytes. Different cell types can generate ApoBDs via different mechanisms [70]. These ApoBDs can be classified based on cell-type-specific surface markers and content. Jiang et al. showed that ApoBDs share the same surface markers as their cell of origin; this is the reason why apoptotic bodies are very different and can

ApoBD occurs spontaneously in untreated malignant neoplasms, and is implicated in both physiological involution and atrophy of various tissues and organs. Pathological settings include inflammation [71], autoimmunity [72–74], viral infection [75], and tumorigenesis because they participate in the horizontal transfer

of oncogenes due to their nuclear material content from the dying cells [76].

Tumor masses are composed of cancer cells and stromal cells, in which one include mesenchymal cells, fibroblasts and immune cells, and extracellular matrix (ECM) components. All these cells emit EVs and participate in the creation of a unique tumor nanoenvironment. EVs are capable of horizontal transfer of bioactive content to interact with cells in the tumor microenvironment. These interactions can include fusion of the EV with the plasmalemma of the recipient cell or endocytosis of the EVs [77]. EVs represent the bidirectional way of interaction between stromal and cancer cells as a mean to exchange information and modify the tumor microenvironment. Therefore, the content of these vesicles is of great significance in the evolution of the cancer, since it was shown to modulate the complex signaling

Circulating DNA can be found in free form or contained in EVs and is thought to be the future in cancer diagnosis and treatment monitoring. This will be possible because the DNA fragments contained in EVs are relatively intact (average 15 kbp) by comparison with the circulating cell-free one (average 130 bp) due to the protection offered by the lipid bilayer [79]. Vagner et al. showed in a very recent study that the majority of the extracellular DNA is contained in large oncosomes, rather than in exosomes, both in vitro and in the patients' plasma and has all cancer-specific genomic alterations [80]. The majority of the DNA contained

**3. Extracellular vesicles and tumor microenvironment**

networks that facilitate tumor progression [78].

role in cell migration, angiogenesis, and cancer progression and metastasis [28]. Oncosomes allow intercellular transfer of oncogenes, hence the motivation to be considered as existing biomarkers in the blood or plasma of patients for the detection of cancer [67].
