Role of tumor cytoskeleton and membrane glycoprotein IRGpIIb/IIIa in platelet adhesion to tumor cell membrane and tumor cell-induced platelet aggregation

Components of the tumor cell cytoskeleton (i.e., microtubules, microfilaments, and intermediate filaments) have been reported to affect metastatic ability, since disruption of these components leads to a decrease in metastasis. One mechanism of metastasis which has not been previously considered is the decreased interaction of tumor cells with platelets. We present evidence that disruption of the tumor cell cytoskeleton decreases the ability of tumor cells to aggregate homologous platelets. This effect is dependent upon the disruption of microfilaments/intermediate filaments but not disruption of microtubules. In addition, tumor cell platelet interactions require the lateral mobility of specific receptors (i.e., clustering) on the tumor cell plasma membrane. A membrane glycoprotein immunologically related to the platelet glycoprotein IIb/IIIa complex was identified on Walker 256 carcinosarcoma cells using specific polyclonal and monoclonal antibodies and Northern blot analysis using complementary DNA probes for IIb and IIIa. Mobility of this receptor is dependent upon tumor cell microfilaments/intermediate filaments, but not microtubules. Furthermore, treatment of tumor cells with specific antibodies to the platelet glycoprotein IIb/IIIa complex inhibits tumor cell-platelet interaction at the macroscopic level (i.e., aggregation) and at the ultrastructural level (i.e., platelet adhesion to the tumor cell surface). These results suggest that this immunologically related glycoprotein IIb/IIIa is a receptor for platelet binding to the tumor cell surface, an event which precedes overt platelet aggregation and is dependent upon an intact tumor cell microfilament and intermediate filament network. Therefore, the decreased metastasis observed by others following disruption of the tumor cell cytoskeleton may be due, in part, to a decreased tumor cell-platelet interaction.     

Adhesion molecules and tumor cell interaction with endothelium and subendothelial matrix

Cancer metastasis poses the greatest challenge to the eradication of malignancy. The majority of clinical and experimental evidence indicates that metastasis is a non-random, organ-specific process. Tumor cell interaction with endothelium and subendothelial matrix constitutes the most crucial factor in determining the organ preference of metastasis. A plethora of cell surface adhesion molecules, which encompass four major families (i.e., integrins, cadherins, immunoglobulins and selectins) and many other unclassified molecules, mediate tumor-host interactions. Adhesion molecules and adhesion processes are involved in most, if not all, of the intermediate steps of the metastatic cascade. Decreased E-cadherin expression and increased CD44 expression are clearly correlated with the acquisition of the invasive capacity of primary tumor cells. Similarly, altered expression pattern of many other adhesion molecules such as upregulated expression of the laminin receptors and depressed expression of fibronectin receptors (51) appears to be involved in tumor cell invasion into the subendothelial matrix. Tumor cell-endothelium interactions involve several well-defined sequential steps that can be analyzed by the Docking and Locking hypothesis at the molecular level. Tumor cell-matrix interactions are determined by the repertoire of adhesion receptors of tumor cells and the unique composition of organ-specific matrices. Our experimental data, together with others', suggest that the integrin IIb3 is one of the major players in these tumor-host interactions. Tumor-host interaction is a dynamic process which is constantly modulated by a host of factors including various cytokines, growth factors and arachidonate metabolites such as 12(S)-HETE. Delineation of the molecular mechanisms of tumor-host interactions may provide additional means to intervene in the metastatic process.     

血小板内皮细胞黏附分子-1与肿瘤

血小板内皮细胞黏附分子-1（PECAM-1）是免疫球蛋白超家族中的一种黏附分子,高表达于内皮细胞.近年来研究发现,PECAM-1与肿瘤的发生、血管生成、细胞凋亡以及耐药均相关,可能对肿瘤的诊断与治疗产生重要影响.     

Biology of tumor cell invasion: Interplay of cell adhesion and matrix degradation

Invasion of malignant cells requires altered cellular interaction with extracellular matrix. Integrin-type cell adhesion receptors play an important role in this process. Integrin-related cell biological phenomena explain cancer cell migration, and recent developments in the field have made it possible to propose that integrins are also involved in the penetration through basement membranes and other molecular barriers. Finally, malignant melanoma has been used here as an example to speculate on the function of each integrin in light of information from different experimental models. © 1996 Wiley-Liss, Inc.     

Platelet-tumor cell interaction with the subendothelial extracellular matrix: relationship to cancer metastasis

Dissemination of neoplastic cells within the body involves invasion of blood vessels by tumor cells. This requires adhesion of blood-borne cells to the luminal surface of the vascular endothelium, invasion through the endothelial cell layer and local dissolution of the subendothelial basement membrane. Platelets may participate in each of these steps and thus play a role in the pathogenesis of tumor cell metastasis. To learn more about the possible involvement of platelets we studied the interaction of platelets and tumor cells with cultured vascular endothelial cells and their secreted basement membrane-like extracellular matrix (ECM). Whereas the apical surface of the vascular endothelium lacks adhesive glycoproteins and hence protect the vessel wall against platelet and tumor cell adhesion, the underlying ECM constitute a highly adhesive and thrombogenic surface. Interaction of platelets with this ECM was associated with platelet activation, aggregation and degradation of heparan sulfate in the ECM by means of the platelet heparitinase. The activity of a similar enzyme has been previously correlated with the metastatic potential of various tumor sublines. Biochemical and scanning electron microscopy (SEM) studies have demonstrated that platelets may detect even minor gaps between adjacent endothelial cells and degrade the ECM heparan sulfate. This may expose a larger area of the subendothelium and facilitate subsequent adhesion of blood borne tumor cells. Platelets were also shown to recruit lymphoma cells into minor gaps in the vascular endothelium, that otherwise do not constitute a preferential site of invasion. It is suggested that the platelet heparitinase is involved in the impairment of the integrity of the vessel wall and thus play a role in tumor cell metastasis.     

Clinging to life: cell to matrix adhesion and cell survival

Cell to matrix adhesion regulates cellular homeostasis in multiple ways. Integrin attachment to the extracellular matrix mediates this regulation through direct and indirect connections to the actin cytoskeleton, growth factor receptors, and intracellular signal transduction cascades. Disruption of this connection to the extracellular matrix has deleterious effects on cell survival. It leads to a specific type of apoptosis known as anoikis in most non-transformed cell types. Anchorage independent growth is a critical step in the tumorigenic transformation of cells. Thus, breaching the anoikis barrier disrupts the cell's defenses against transformation. This review examines recent investigations into the molecular mechanisms of anoikis to illustrate current understanding of this important process.     

膜型基质金属蛋白酶-1在肿瘤中的作用

膜型基质金属蛋白酶（membrane—type matrix metalloproteinase,MT—MMP）是一类基质金属蛋白酶（matrix metalloproteinases,MMPs）家族的新成员,膜型基质金属蛋白酶-1（MT1-MMP／MMP14）是第一个鉴别出的膜型基质金属蛋白酶,它直接或间接降解细胞外基质中的多种成分,通过调节多种细胞效应分子影响肿瘤细胞的增殖和凋亡,细胞迁移,肿瘤细胞的浸润、转移以及血管生成等过程,在肿瘤的发生发展过程中有重要作用。     

An in vivo study of the role of the tumor cell cytoskeleton in tumor cell-platelet-endothelial cell interactions

We recently reported that disruption of tumor cell microfilaments or intermediate filaments resulted in an inhibition of the ability of tumor cells to induce the aggregation of homologous platelets in vitro (H. Chopra et al., Cancer Res., 48: 3787-3800, 1988). Previous investigators demonstrated that disruption of the tumor cell cytoskeleton decreases the ability of these cells to form lung colonies. We proposed that this latter effect is due, in part, to decreased interaction of tumor cells with platelets, following their arrest in the microvasculature. To test this hypothesis, B16 amelanotic melanoma cell microtubules, microfilaments, or vimentin intermediate filaments were disrupted with colchicine (50 microns), cytochalasin D (50 microns), or cycloheximide (50 microns), respectively, and then cells were tail vein injected into syngeneic mice. Both cytochalasin D- and cycloheximide-treated cells formed fewer lung colonies than did control cells. Colchicine, however, failed to inhibit lung colony formation. Neither colchicine nor cycloheximide treatment altered initial pulmonary arrest; however, fewer cycloheximide-treated cells remained in the lungs 8 h postinjection. Greater than 90% of control or colchicine-treated cells were found to be associated with activated platelets, and they also demonstrated typical cell membrane process formation 10 min and 8 h post-tumor cell injection. In contrast, less than 10% of cycloheximide-treated cells were in contact with activated platelets 10 min postinjection. However, by 8 h approximately 90% of cycloheximide-treated cells were in contact with activated platelets. This recovery coincided with the reformation of the B16 amelanotic melanoma vimentin intermediate filament network and the reacquisition of the ability to induce platelet aggregation in vitro. Neither colchicine nor cycloheximide treatment altered initial B16 amelanotic melanoma cell adhesion to murine microvessel-derived endothelial cells. This study provides in vivo evidence in support of our previous findings that disruption of certain cytoskeletal elements (i.e., vimentin intermediate filaments) inhibits the tumor cell ability to activate platelets. This study also suggests that platelet activation may stabilize the initial tumor cell arrest in the microvasculature.     

The role of the cytoskeleton in differentially regulating pressure-mediated effects on malignant colonocyte focal adhesion signaling and cell adhesion

Increased extracellular pressure stimulates colon cancer cell adhesion by activating focal adhesion kinase (FAK) and Src. We investigated the role of the cytoskeleton in pressure-induced inside-out FAK and Src phosphorylation and pressure-stimulated adhesion. We perturbed actin polymerization with phalloidin, cytochalasin D and latrunculin B, and microtubule organization with colchicine and paclitaxol. We compared the effects of these agents on pressure-induced SW620 and human primary colon cancer cell adhesion and inside-out FAK/Src activation with outside-in adhesion-dependent FAK/Src activation. Cells pretreated with cytoskeletal inhibitors were subjected to 15 mmHg increased pressure and allowed to adhere to collagen I coated plates or prevented from adhesion to pacificated plates for 30 min. Phalloidin, cytochalasin D, latrunculin B and colchicine pretreatment completely prevented pressure-stimulated and significantly inhibited basal SW620 cell adhesion. Taxol did not inhibit pressure-induced colon cancer cell adhesion, but significantly lowered basal adhesion. Cytochalasin D and colchicine had similar effects in pressure-stimulated primary human malignant colonocytes. Phalloidin, cytochalasin D, latrunculin B and colchicine prevented pressure-induced SW620 FAK phosphorylation but not Src phosphorylation. FAK phosphorylation in response to collagen I adhesion was significantly attenuated but not completely prevented by these inhibitors. Although Src phosphorylation was not increased on adhesion, the cytoskeleton disrupting agents significantly lowered basal Src phosphorylation in adherent cells. These results suggest that both cytoskeleton-dependent FAK activation and cytoskeleton-independent Src activation may be required for extracellular pressure to stimulate colon cancer cell adhesion. Furthermore, the cytoskeleton plays a different role in pressure-activated FAK and Src signaling than in FAK and Src activation in adherent cells. We, therefore, hypothesize that cytoskeletal interactions with focal adhesion signals mediate the effects of extracellular pressure on colon cancer cell adhesion.     

The functional role of cell adhesion molecules in tumor angiogenesis

Cell adhesion molecules (CAMs) are cell surface glycoproteins that mediate the physical interactions between adjacent cells and between cells and the surrounding extracellular matrix. CAMs belong to different protein families, depending on their structural and functional properties. Furthermore, the expression of certain CAMs under physiological conditions is restricted to specific cell types. Besides playing a key homeostatic role in maintaining the architecture of quiescent tissues, CAMs have also to adapt to the microenvironmental changes that occur during certain physiological and pathological processes. This is best exemplified by cancer vascularization, where the expression and function of vascular CAMs are dynamically regulated in response to tissue alterations induced by tumor growth as well as by changes in the surrounding stroma. This enables endothelial cells (ECs) to leave the quiescent state and re-enter the angiogenic cascade. The latter is a multistep process carried out by different types of specialized ECs. This review describes the actual or supposed function of the various CAM subsets in the sequential series of events that underlie vascular changes during tumor angiogenesis. Notably, elucidating the mechanism of action of endothelial CAMs in cancer vasculature is expected to open new therapeutic avenues aimed at interfering with tumor growth and dissemination.     

Platelets mediate tumor cell adhesion to the subendothelium under flow conditions: Involvement of platelet GPIIb-IIIa and tumor cell αv integrins

The aim of our study was to explore the role of platelets and their specific integrin receptors in mediating the interaction of 4 human tumor cell lines (3 melanoma and 1 carcinoma) with the extracellular matrix (ECM) under static and arterial flow conditions. Under static conditions, all 4 cell lines adhered to the ECM. The adhesion capacity of all 4 cell lines was virtually abolished by application of flow during incubation with the ECM. Under static conditions, tumor cell adhesion was not affected by adding platelets to the cell suspension and was slightly reduced by pre-coating the ECM with platelets prior to the addition of tumor cells. In contrast, under flow conditions, platelets significantly increased tumor cell adhesion to the ECM, the enhancing effect being more pronounced when platelets were pre-incubated with the ECM prior to the addition of tumor cells than when incubated simultaneously with the cells. Platelet-mediated tumor cell adhesion under flow was markedly inhibited by blockade of the platelet GPIIb-IIIa or of the tumor cell α_v integrins. Platelets of a Glanzmann thrombastenia (GT) patient were unable to support tumor cell adhesion to the ECM under flow. Our results suggest that the interaction of tumor cells with subendothelium-bound platelets under flow conditions is mediated by platelet GPIIb-IIIa and by tumor cell α_v integrins independently of the nature of the β subunit. Int. J. Cancer, 70:201–207, 1997. © 1997 Wiley-Liss, Inc.     

Monocyte differentiation induced by co-culture with tumor cells involves RGD-dependent cell adhesion to extracellular matrix

Macrophages that infiltrate tumor tissues, or tumor-associated macrophages (TAMs), affect the malignant behaviors of tumor cells. In this study, we attempted to induce monocytes to differentiate into TAM-like cells producing matrix metalloproteinases (MMPs) by co-culture with tumor cells. When human monocytes were co-cultured for 3-7 days with tumor cell lines, monocytes differentiated to produce MMP-9, accompanied by morphological changes. The in vitro cell invasion of MKN1 human gastric carcinoma cells into Matrigel membranes was promoted in the presence of differentiated monocytes, and the enhancement of cell invasion by differentiated monocytes was correlated with their MMP-9 productivity. The addition of an RGD (Arg-Gly-Asp) peptide to the culture significantly inhibited monocyte differentiation. The MMP-9 production from monocytes was diminished by the depletion of fibronectin from the conditioned media with gelatin-Sepharose, and potentiated by culturing them in fibronectin-coated plates. These results suggest that cell adhesion to the extracellular matrix plays a crucial role in monocyte differentiation into TAM-like cells.     

Morphological study of the interaction of intravascular tumor cells with endothelial cells and subendothelial matrix

Multiple steps or events have been described as essential in the metastatic cascade. Tail vein injection of single cell suspensions was used to study the ultrastructural details of the events involved in the initial arrest and attachment of circulating tumor cells. Lewis Lung Carcinoma (3LL) and a mammary adenocarcinoma (16c) were compared to a previous ultrastructural study of B16 amelanotic melanoma (B16a) detailing morphological events in the initial arrest and attachment of tumor cells in lung. The three murine tumors followed similar steps and varied only slightly in the time sequence of the steps. We observed the following steps: (a) initial arrest of tumor cells was characterized by an intimate tumor endothelial cell contact; (b) platelet activation and aggregation was noted by two minutes. Platelet aggregation continued for 1-4 h until a thrombus formed; (c) after approximately 4 h endothelial cell separation with extension of the tumor cell to the subendothelial matrix was noted; (d) at approximately 24 h the tumor cell associated thrombus dissipated and the attached tumor cells were exposed to a reestablished circulation. (e) mitoses were observed after 24 h with cell division and the development of intravascular tumor nodules; (f) the final step in the extravasation sequence was dissolution of the basement membrane by the attached tumor cells.     

Degradation of basement membrane type IV collagen and lung subendothelial matrix by rat mammary adenocarcinoma cell clones of differing metastatic potentials

A series of rat 13762NF mammary adenocarcinoma cell clones and subclones of various lung metastatic potentials were examined for their abilities to degrade rat lung subendothelial matrix and purified basement membrane type IV collagen. Metastatic potentials were simultaneously determined based on the ability to form "spontaneous" lung metastases after s.c. injection or "experimental" lung metastases after i.v. injection of cells. Microvessel endothelial cells isolated from rat lung were grown in vitro, and the subendothelial matrix containing type IV collagen was metabolically labeled with [3H]proline. When mammary adenocarcinoma cells were placed on the isolated subendothelial matrix, fragmentation and solubilization of [3H]proline-labeled components were observed; highly metastatic 13762NF cells solubilized the matrix at higher rates than did poorly metastatic cells. The 13762NF cells were assayed for type IV collagenolytic activity using [3H]proline-labeled type IV collagen purified from Engelbreth-Holm-Swarm tumor as a substrate. We found excellent correlation between the type IV collagenolytic activities of living cells and their "spontaneous" lung metastatic potentials (r = 0.993). The levels of type IV collagenolytic activity in the conditioned medium depended on the cell culture conditions. In the presence or absence of acid-treated fetal bovine serum, highly metastatic cells secreted higher amounts of type IV collagenolytic enzymes in active and latent forms than did poorly metastatic cells. Incubation of procollagen type IV with medium conditioned by highly metastatic 13762NF cells and treated with trypsin resulted in the production of several large fragments characteristic of type IV collagen. The results suggest that enzymatic degradation of basement membrane type IV collagen is important in lung metastasis of 13762NF mammary adenocarcinoma cells.     

Tumor cell adhesion to the extracellular matrix and signal transduction mechanisms implicated in tumor cell motility,invasion and metastasis

Summary The relationship between tumor cell adhesion to the extracellular matrix (ECM) and invasion and metastasis formation is one of the most intensively studied topics in cancer biology within the last 10–15 years. The aberrant molecular relationships between malignant tumor cells and their surrounding ECM have been implicated at virtually every stage of the metastatic process; ranging from steps that involve the local invasion of tumor cells away from the primary tumor to those that are involved in mediating extravasation through microvessel-associated basement membranes at the site(s) of metastasis formation. The complexity of tumor metastasis has required that a reductionist approach be taken in order to identify and relate specific molecular mechanisms involved in tumor cell adhesion to various aspects of tumor metastasis. The intensive research efforts into cell adhesion and tumor cell biology have generated many significant new concepts towards our understanding of the molecular aspects of tumor cell adhesion and metastasis. Our purpose in this article is to briefly summarize the relationship of ECM-stimulated tumor cell adhesion to the processes of tumor cell motility and invasion. This is followed by a discussion of certain aspects of signal transduction pathways that may impact on cell motility, with an emphasis on the relationship between phosphatidylinositol hydrolysis and actin polymerization, as well as certain GTP-binding protein-(G-protein) mediated events that could influence cytoskeletal organization and cell motility. Our emphasis is based on increasing evidence that implicates members of the signal transduction G-proteins in the motility and invasion of many normal and transformed cells.     

Thrombin stimulates melanoma tumor-cell binding to endothelial cells and subendothelial matrix

Activation by point mutation of the H-, K- and N-ras genes is found in many tumors. However, no such mutation has yet been found in human esophageal carcinomas from various parts of the world. We have confirmed the absence of mutation at codons 12, 13 and 61 of K- and N-ras and at codons 12 and 61 of H-ras in 25 primary tumors obtained in France. In contrast, among 7 human esophageal carcinoma cell lines (TE1, TE2, TE3, TE8, TE9, TE TE10, TE 13) with different degrees of tumorigenicity in nude mice, 3 highly tumorigenic lines (TE1, TE2 and TE8) exhibited activation of ras oncogenes; 2 showed a G³⁵ to A³⁵ transition of K-ras gene and one a H-ras G³⁵ to T³⁵ transversion. Since these cell lines had been established from tumors of Japanese patients from Sendai, we examined 3 primary esophageal tumors from Tokyo and 19 from Sendai, including the primary tumors from which the TE cell lines had been derived. No ras mutation was detected, which suggests that the ras gene mutations in the TE cell lines are either due to their long-term culture or that only a small portion of the original tumors contained such mutations. In order to directly examine the effect of ras gene mutation, one of the non-tumorigenic cell lines, TE 13, was transfected with a plasmid coding for a mutated H-ras gene (G³⁵ to T³⁵). Transfected clones expressing high levels of mutated ras gene were able to induce tumors in nude mice. Thus, although no primary human esophageal tumor contained mutated ras genes, our studies do not exclude a significant role of mutated ras genes in cell proliferation and malignant transformation of human esophageal cells.     

Resensitization of breast cancer cells to anoikis by tropomyosin-1: role of Rho kinase-dependent cytoskeleton and adhesion

Two most common properties of malignant cells are the presence of aberrant actin cytoskeleton and resistance to anoikis. Suppression of several key cytoskeletal proteins, including tropomyosin-1 (TM1), during neoplastic transformation is hypothesized to contribute to the altered cytoskeleton and neoplastic phenotype. Using TM1 as a paradigm, we have shown that cytoskeletal proteins induce anoikis in breast cancer (MCF-7 and MDA MB 231) cells. Here, we have tested the hypothesis that TM1-mediated cytoskeletal changes regulate integrin activity and the sensitivity to anoikis. TM1 expression in MDA MB 231 cells promotes the assembly of stress fibers, induces rapid anoikis via caspase-dependent pathways involving the release of cytochrome c. Further, TM1 inhibits binding of MDA MB 231 cells to collagen I, but promotes adhesion to laminin. Inhibition of Rho kinase disrupts TM1-mediated cytoskeletal reorganization and adhesion to the extracellular matrix components, whereas the parental cells attach to collagen I, spread and form extensive actin meshwork in the presence of Rho kinase inhibitor, underscoring the differences in parental and TM1-transduced breast cancer cells. Further, treatment with the cytoskeletal disrupting drugs rescues the cells from TM1-induced anoikis. These new findings demonstrate that the aberrant cytoskeleton contributes to neoplastic transformation by conferring resistance to anoikis. Restoration of stress fiber network through enhanced expression of key cytoskeletal proteins may modulate the activity of focal adhesions and sensitize the neoplastic cells to anoikis.     

Thrombin promotes platelet-mediated melanoma cell adhesion to endothelial cells under flow conditions: role of platelet glycoproteins P-selectin and GPIIb-IIIA.

We investigated the role of platelets in human melanoma cell (line 397) interaction with vascular endothelial cells (ECs) under flow conditions. The ability of the tumour cells to adhere to the EC monolayer was significantly reduced by application of flow at a shear rate of 250 s(-1). A 2.2-fold increase in tumour cell adhesion to ECs under flow was observed upon addition of thrombin receptor agonist peptide (TRAP)-activated platelets but not resting platelets. A similar increase (2.5-fold) in tumour cell adhesion to ECs under flow was observed when the tumour cells were incubated with resting platelets on thrombin-treated ECs. However, thrombin treatment of the ECs alone had no effect on tumour cell adhesion in the absence of platelets. The enhancement of tumour cell adhesion to ECs by TRAP-activated platelets was virtually abolished by blockade of the platelet glycoproteins P-selectin and GPIIb-IIIa by monoclonal antibodies. Blockade of P-selectin also inhibited the direct adhesion of TRAP-activated platelets to ECs, but did not affect the interaction of the tumour cells with platelets immobilized on subendothelial extracellular matrix (ECM). Blockade of GPIIb-IIIa inhibited both platelet-EC and platelet-tumor cell interactions. Our results indicate that tumour cell adhesion to the endothelium under flow is enhanced by platelets under conditions that allow platelet adhesion to ECs. Inhibition studies suggest that activated platelet adhesion to ECs is mediated by P-selectin and GPIIb-IIIA, and tumour cell adhesion to EC-bound platelets--mainly by GPIIb-IIIa.     

The role of vascular cell adhesion molecule-1 in tumor immune evasion

Tumor immune escape is a critical trait of cancer but the mechanisms involved have yet to fully emerge. One recent study has shown that tumor cells can escape T-cell immunity by overexpressing the endothelial cell adhesion molecule vascular cell adhesion molecule-1 (VCAM-1), which normally mediates leukocyte extravasion to sites of tissue inflammation. Renal cell carcinoma (RCC) was identified as one tumor type where VCAM-1 is commonly highly overexpressed. Together, our findings suggest that RCCs might exploit VCAM-1 overexpression for immune escape.     

上皮细胞黏附分子在肿瘤中的研究

 上皮细胞黏附分子（EpCAM）是通过与核受体结合从而在基因表达调控过程中发挥重要作用。大量研究表明,EpCAM在乳腺癌、肺癌、胃癌等多种肿瘤呈过表达。EpCAM在肿瘤循环细胞富集、肿瘤发病机制以及预后作用中的研究,将有助于肿瘤靶向治疗取得新的突破。