Angiotropism of human prostate cancer cells: implications for extravascular migratory metastasis

Role of elastic fiber degradation in disease pathogenesis

Elastin is a crucial extracellular matrix protein that provides structural integrity to tissues. Crosslinked elastin and associated microfibrils, named elastic fiber, contribute to biomechanics by providing the elasticity required for proper function. During aging and disease, elastic fiber can be progressively degraded and since there is little elastin synthesis in adults, degraded elastic fiber is not regenerated. There is substantial evidence linking loss or damage of elastic fibers to the clinical manifestation and pathogenesis of a variety of diseases. Disruption of elastic fiber networks by hereditary mutations, aging, or pathogenic stimuli results in systemic ailments associated with the production of elastin degradation products, inflammatory responses, and abnormal physiology. Due to its longevity, unique mechanical properties, and widespread distribution in the body, elastic fiber plays a central role in homeostasis of various physiological systems. While pathogenesis related to elastic fiber degradation has been more thoroughly studied in elastic fiber rich tissues such as the vasculature and the lungs, even tissues containing relatively small quantities of elastic fibers such as the eyes or joints may be severely impacted by elastin degradation. Elastic fiber degradation is a common observation in certain hereditary, age, and specific risk factor exposure induced diseases representing a converging point of pathological clinical phenotypes which may also help explain the appearance of co-morbidities. In this review, we will first cover the role of elastic fiber degradation in the manifestation of hereditary diseases then individually explore the structural role and degradation effects of elastic fibers in various tissues and organ systems. Overall, stabilizing elastic fiber structures and repairing lost elastin may be effective strategies to reverse the effects of these diseases.

Directed movement toward, translocation along, penetration into and exit from vascular networks by breast cancer cells in 3D

We developed a computer-assisted platform using laser scanning confocal microscopy to 3D reconstruct in real-time interactions between metastatic breast cancer cells and human umbilical vein endothelial cells (HUVECs). We demonstrate that MB-231 cancer cells migrate toward HUVEC networks, facilitated by filopodia, migrate along the network surfaces, penetrate into and migrate within the HUVEC networks, exit and continue migrating along network surfaces. The system is highly amenable to 3D reconstruction and computational analyses, and assessments of the effects of potential anti-metastasis monoclonal antibodies and other drugs. We demonstrate that an anti-RHAMM antibody blocks filopodium formation and all of the behaviors that we found take place between MB-231 cells and HUVEC networks.

Angiotropism, pericytic mimicry and extravascular migratory metastasis: an embryogenesis-derived program of tumor spread

Intravascular dissemination of tumor cells is the accepted mechanism of cancer metastasis. However, the phenomenon of angiotropism, pericyte mimicry (PM), and extravascular migratory metastasis (EVMM) has questioned the concept that tumor cells metastasize exclusively via circulation within vascular channels. This new paradigm of cancer spread and metastasis suggests that metastatic cells employ embryonic mechanisms for attachment to the abluminal surfaces of blood vessels (angiotropism) and spread via continuous migration, competing with and replacing pericytes, i.e., pericyte mimicry (PM). This is an entirely extravascular phenomenon (i.e., extravascular migratory metastasis or EVMM) without entry (intravasation) into vascular channels. PM and EVMM have mainly been studied in melanoma but also occur in other cancer types. PM and EVMM appear to be a reversion to an embryogenesis-derived program. There are many analogies between embryogenesis and cancer progression, including the important role of laminins, epithelial-mesenchymal transition, and the re-activation of embryonic signals by cancer cells. Furthermore, there is no circulation of blood during the first trimester of embryogenesis, despite the fact that there is extensive migration of cells to distant sites and formation of organs and tissues during this period. Embryonic migration therefore is a continuous extravascular migration as are PM and EVMM, supporting the concept that these embryonic migratory events appear to recur abnormally during the metastatic process. Finally, the perivascular location of tumor cells intrinsically links PM to vascular co-option. Taken together, these two new paradigms may greatly influence the development of new effective therapeutics for metastasis. In particular, targeting embryonic factors linked to migration that are detected during cancer metastasis may be particularly relevant to PM/EVMM.

Pericytes in Sarcomas and Other Mesenchymal Tumors

Tumors of mesenchymal origin are a diverse group, with >130 distinct entities currently recognized by the World Health Organization. A subset of mesenchymal tumors grow or invade in a perivascular fashion, and their potential relationship to pericytes is a matter of ongoing interest. In fact, multiple intersections exist between pericytes and tumors of mesenchymal origin. First, pericytes are the likely cell of origin for a group of mesenchymal tumors with a common perivascular growth pattern. These primarily benign tumors grow in a perivascular fashion and diffusely express canonical pericyte markers such as CD146, smooth muscle actin (SMA), platelet-derived growth factor receptor beta (PDGFR-β), and RGS5. These benign tumors include glomus tumor, myopericytoma, angioleiomyoma, and myofibroma. Second and as suggested by animal models, pericytes may give rise to malignant sarcomas. This is not a suggestion that all sarcomas within a certain subtype arise from pericytes, but that genetic modifications within a pericyte cell type may give rise to sarcomas. Third, mesenchymal tumors that are likely not a pericyte derivative co-opt pericyte markers in certain contexts. These include the PEComa family of tumors and liposarcoma. Fourth and finally, as "guardians" that enwrap the microvasculature, nonneoplastic pericytes may be important in sarcoma disease progression.

Angiotropism in recurrent cutaneous squamous cell carcinoma: Implications for regional tumor recurrence and extravascular migratory spread

Extravascular migratory metastasis is a form of cancer metastasis in which tumor cells spread by tracking along the abluminal aspect of vessel walls without breaking the vascular endothelial lining or intraluminal invasion. This phenomenon has been extensively described in melanoma and is being increasingly recognized in other neoplasms. Various modalities of treatment, including radiation-, chemo-, targeted-, and immune- therapies may potentially induce angiotropic behavior in neoplastic cells. Although there is a risk for tumor recurrence and metastasis, angiotropism may be under-recognized and is rarely reported. Here, we report a case of recurrent poorly-differentiated acantholytic squamous cell carcinoma of the scalp with extensive perineural invasion, previously treated with multiple therapies. There was multifocal extravascular cuffing of neoplastic cells around and focally involving the walls of small to medium-caliber blood vessels within and surrounding the tumor, without obvious tumor intravasation. In addition, small subtle nests of neoplastic keratinocytes were noted along the abluminal aspect of a large-caliber deep dermal blood vessel in an en-face margin, away from the main tumor mass. Such involvement can be difficult to identify; and thus, may be missed particularly during intra-operative frozen section evaluation, leading to false-negative margins and is therefore, a diagnostic pitfall.

Angiotropism and extravascular migratory metastasis in cutaneous and uveal melanoma progression in a zebrafish model

Cutaneous melanoma is a highly aggressive cancer with a propensity for distant metastasis to various organs. In contrast, melanoma arising in pigmented uveal layers of the eye metastasizes mostly in the liver. The mechanisms of these metastases, which are ultimately resistant to therapy, are still unclear. Metastasis via intravascular dissemination of tumour cells is widely accepted as a central paradigm. However, we have previously described an alternative mode of tumour dissemination, extravascular migratory metastasis, based on clinical and experimental data. This mechanism is characterised by the interaction of cancer cells with the abluminal vascular surface, which defines angiotropism. Here, we employed our 3D co-culture approach to monitor cutaneous and uveal human melanoma cells dynamics in presence of vascular tubules. Using time-lapse microscopy, we evaluated angiotropism, the migration of tumour cells along vascular tubules and the morphological changes occurring during these processes. Cutaneous and uveal melanoma cells were injected in zebrafish embryos in order to develop xenografts. Employing in vivo imaging coupled with 3D reconstruction, we monitored the interactions between cancer cells and the external surface of zebrafish vessels. Overall, our results indicate that cutaneous and uveal melanoma cells spread similarly along the abluminal vascular surfaces, in vitro and in vivo.

Pericytic mimicry in well-differentiated liposarcoma/atypical lipomatous tumor

Pericytes are modified smooth muscle cells that closely enwrap small blood vessels, regulating and supporting the microvasculature through direct endothelial contact. Pericytes demonstrate a distinct immunohistochemical profile, including expression of smooth muscle actin, CD146, platelet-derived growth factor receptor β, and regulator of G-protein signaling 5. Previously, pericyte-related antigens have been observed to be present among a group of soft tissue tumors with a perivascular growth pattern, including glomus tumor, myopericytoma, and angioleiomyoma. Similarly, malignant tumor cells have been shown to have a pericyte-like immunoprofile when present in a perivascular location, seen in malignant melanoma, glioblastoma, and adenocarcinoma. Here, we examine well-differentiated liposarcoma specimens, which showed some element of perivascular areas with the appearance of smooth muscle (n = 7 tumors). Immunohistochemical staining was performed for pericyte antigens, including smooth muscle actin, CD146, platelet-derived growth factor receptor β, and regulator of G-protein signaling 5. Results showed consistent pericytic marker expression among liposarcoma tumor cells within a perivascular distribution. MDM2 immunohistochemistry and fluorescence in situ hybridization for MDM2 revealed that these perivascular cells were of tumor origin (7/7 tumors), whereas double immunohistochemical detection for CD31/CD146 ruled out an endothelial cell contribution. These findings further support the concept of pericytic mimicry, already established in diverse malignancies, and its presence in well-differentiated liposarcoma. The extent to which pericytic mimicry has prognostic significance in liposarcoma is as yet unknown.

Imaging of Angiotropism/Vascular Co-Option in a Murine Model of Brain Melanoma: Implications for Melanoma Progression along Extravascular Pathways

Angiotropism/pericytic mimicry and vascular co-option involve tumor cell interactions with the abluminal vascular surface. These two phenomena may be closely related. However, investigations of the two processes have developed in an independent fashion and different explanations offered as to their biological nature. Angiotropism describes the propensity of tumor cells to spread distantly via continuous migration along abluminal vascular surfaces, or extravascular migratory metastasis (EVMM). Vascular co-option has been proposed as an alternative mechanism by which tumors cells may gain access to a blood supply. We have used a murine brain melanoma model to analyze the interactions of GFP human melanoma cells injected into the mouse brain with red fluorescent lectin-labeled microvascular channels. Results have shown a striking spread of melanoma cells along preexisting microvascular channels and features of both vascular co-option and angiotropism/pericytic mimicry. This study has also documented the perivascular expression of Serpin B2 by angiotropic melanoma cells in the murine brain and in human melanoma brain metastases. Our findings suggest that vascular co-option and angiotropism/pericytic mimicry are closely related if not identical processes. Further studies are needed in order to establish whether EVMM is an alternative form of cancer metastasis in addition to intravascular cancer dissemination.

Pericyte antigens in angiomyolipoma and PEComa family tumors

Perivascular epithelioid cell tumors (PEComas) are an uncommon family of soft tissue tumors with dual myoid-melanocytic differentiation. Although PEComa family tumors commonly demonstrate a perivascular growth pattern, pericyte antigen expression has not yet been examined among this unique tumor group. Previously, we demonstrated that a subset of perivascular soft tissue tumors exhibit a striking pericytic immunophenotype, with diffuse expression of αSMA, CD146, and PDGFRβ. Here, we describe the presence of pericyte antigens across a diverse group of PEComa family tumors (n = 19 specimens). Results showed that pericyte antigens differed extensively by histological appearance. Typical angiomyolipoma (AML) specimens showed variable expression of pericyte antigens among both perivascular and myoid-appearing cells. In contrast, AML specimens with a predominant spindled morphology showed diffuse expression of pericyte markers, including αSMA, CD146, and PDGFRβ. AML samples with predominant epithelioid morphology showed a marked reduction in or the absence of immunoreactivity for pericyte markers. Lymphangiomyoma samples showed more variable and partial pericyte marker expression. In summary, pericyte antigen expression is variable among PEComa family tumors and largely varies by tumor morphology. Pericytic marker expression in PEComa may represent a true pericytic cell of origin, or alternatively aberrant pericyte marker adoption. Markers of pericytic differentiation may be of future diagnostic utility for the evaluation of mesenchymal tumors, or identify actionable signaling pathways for future therapeutic intervention.

Angiotropism, pericytic mimicry and extravascular migratory metastasis in melanoma: an alternative to intravascular cancer dissemination

For more than 15 years, angiotropism in melanoma has been emphasized as a marker of extravascular migration of tumor cells along the abluminal vascular surface, unveiling an alternative mechanism of tumor spread distinct from intravascular dissemination. This mechanism has been termed extravascular migratory metastasis (EVMM). During EVMM, angiotropic tumor cells migrate in a 'pericytic-like' manner (pericytic mimicry) along the external surfaces of vascular channels, without intravasation. Through this pathway, melanoma cells may spread to nearby or more distant sites. Angiotropism is a prognostic factor predicting risk for metastasis in human melanoma, and a marker of EVMM in several experimental models. Importantly, analogies of EVMM and pericytic mimicry include neural crest cell migration, vasculogenesis and angiogenesis, and recent studies have suggested that the interaction between melanoma cells and the abluminal vascular surface induce differential expression of genes reminiscent of cancer migration and embryonic/stem cell state transitions. A recent work revealed that repetitive UV exposure of primary cutaneous melanomas in a genetically engineered mouse model promotes metastatic progression via angiotropism and migration along the abluminal vascular surface. Finally, recent data using imaging of melanoma cells in a murine model have shown the progression of tumor cells along the vascular surfaces. Taken together, these data provide support for the biological phenomenon of angiotropism and EVMM, which may open promising new strategies for reducing or preventing melanoma metastasis.

Extravascular migratory metastasis in gynaecological carcinosarcoma

AIMS

Extravascular migratory metastasis (EVMM) is a potential mechanism of tumour spread reported most extensively in cutaneous melanoma. It has not been described previously in gynaecological malignancies. We describe EVMM in four gynaecological carcinosarcomas.

METHODS AND RESULTS

Extravascular migratory metastasis was observed in an ovarian carcinosarcoma during routine diagnostic assessment. Twenty-three additional, randomly selected gynaecological carcinosarcomas (11 tubo-ovarian and 12 endometrial) were examined retrospectively and EVMM was identified in three of these. Other than the index case, EVMM was a focal finding, identified in 12-18% of slides. The malignant cells demonstrating EVMM appeared sarcomatoid and were distributed abluminally, partly or completely surrounding the endothelium. Affected vessels often showed mural fibrin deposition. Immunohistochemistry for α-smooth muscle actin (SMA), CD31, CD34, D2-40, laminin and type IV collagen was performed on the EVMM-positive cases. The perivascular malignant cells showed more consistent SMA and laminin immunoreactivity than the non-vascular tumour elements.

CONCLUSIONS

Extravascular migratory metastasis is a hitherto unrecognized mechanism of tumour spread in gynaecological carcinosarcomas. The perivascular tumour cells appear to adopt a pericytic phenotype, and this may represent a specific pattern of epithelial-mesenchymal transition. Further studies with pericyte-specific immunohistological markers may better demonstrate the presence and possible prognostic significance of EVMM in gynaecological tumours.

Atypical spitzoid melanocytic neoplasms with angiotropism: a potential mechanism of locoregional involvement

Atypical spitzoid melanocytic neoplasms (ASMN) may prove difficult to distinguish microscopically from melanoma, and their biological behavior may be unpredictable. ASMN may result in regional lymph node (LN) metastases and frequent sentinel lymph node (SLN) deposits. Angiotropism and extravascular migratory metastasis may account for locoregional metastases in melanoma and thus may potentially explain such locoregional involvement in ASMN. Nine ASMN with angiotropism from 2006 to 2010 were studied. Angiotropism was defined as melanocytes closely opposed to the external surfaces of microvascular channels without intravasation. There were 5 women and 4 men aged 6-40 (mean 18.7) years with ASMN involving the head and neck (5), the extremities (3), and the trunk (1), and the lesions ranged in diameters from 3.5 to 10 (mean 6.2) mm. Breslow thicknesses ranged from 0.66 to 5.35 (mean 3.21) mm, 5 lesions Clark level IV and 4 level V, and dermal mitotic rates varied from 1 to 5 (mean 2.4) per square millimeter. Despite follow-up of 6 months or less in 4 subjects, 5 patients showed regional tumor spread based on detection of SLN deposits, local recurrence, or clinical satellite and LN metastases. Four of 5 patients (80%) undergoing SLN biopsy showed nodal positivity with 2 SLN deposits of >6 mm. Among 4 patients not having SLN biopsy, 1 patient developed local LN metastases after 2 years. We report for the first time angiotropism in ASMN and suggest that such angiotropism seems to correlate with and may explain regional tumor spread in this neoplastic system.

Endoscopic ultrasound fine-needle aspiration detection of extravascular migratory metastasis from a remotely located pancreatic cancer

BACKGROUND & AIMS

Tumor cell migration along the periphery of blood vessels to remote sites has been termed extravascular migratory metastasis, which is distinct from direct gross tumor infiltration of blood vessels and from intravascular dissemination. Our objective was to report the presence of malignant perivascular cuffing of the celiac axis in a patient with an apparently early T stage and resectable pancreatic cancer.

METHODS

Case report is presented.

RESULTS

Endoscopic ultrasound (EUS) examination was performed with targeted fine-needle aspiration (FNA) of previously unrecognized perivascular cuffing by computed tomography, which established the presence of celiac axis malignant perivascular cuffing in the setting of a T1 pancreatic cancer.

CONCLUSIONS

EUS FNA might allow identification and tissue confirmation of otherwise unrecognized extravascular migratory metastasis. This finding suggests the potential for EUS FNA to further improve pancreatic cancer staging and to enhance patient care and outcomes.

Angiotropism is an independent predictor of local recurrence and in-transit metastasis in primary cutaneous melanoma

The migration of melanoma cells along the external surface of blood vessels (angiotropism) has recently been proposed as a mechanism for melanoma metastasis (termed extravascular migratory metastasis). To determine whether the presence of angiotropism, as seen in the routine hematoxylin and eosin sections of primary cutaneous melanomas (PCMs), predicts the development of local or in-transit melanoma recurrence, 32 patients with a PCM who developed local or in-transit recurrence were matched for Breslow thickness with 59 "control" patients with a PCM who did not. The slides from both groups of patients were analyzed in a "blinded" manner for evidence of angiotropism. Other histologic and clinical variables were also assessed. Angiotropism was found more often in patients who developed local or in-transit recurrence (cases) compared with those patients who did not (controls) (P=0.02). Variables that showed a statistically significant association with angiotropism on univariate analysis were: increasing Breslow thickness (P<0.0001), greater Clark level (P<0.001), increasing mitotic index (P<0.0001), presence of ulceration (P<0.01), and absence of regression (P<0.05). The median disease-free survival was 72 months for patients with angiotropism and 104 months for those without (P=0.02). On multivariate analysis the presence of angiotropism was an independent predictor of decreased disease-free survival (P=0.02). This is the first reported study to identify a statistically significant association between the development of local or in-transit recurrence of PCM and the histologic presence of angiotropism and that angiotropism is an independent predictor of decreased disease-free survival, as far as we are aware. Our findings support the hypothesis that angiotropism represents a pathogenic mechanism for metastasis in patients with PCM.

Angiotropic melanoma and extravascular migratory metastasis: a review

How metastases develop is poorly understood. The concept of intravascular dissemination of cancer cells has been widely accepted as a central paradigm. In addition to this explanation, however, other mechanisms may be operable. Ultrastructural studies have identified in malignant melanoma an angio-tumoral complex, in which tumor cells are linked to endothelium by a matrix containing laminin without evidence of intravasation. This observation has suggested that melanoma cells may migrate along the external surface of vessels and other anatomic structures, a mechanism termed "extravascular migratory metastasis" (EVMM). Angiotropism (melanoma cells cuffing the external surface of vessels) is the histopathologic counterpart of the angio-tumoral complex. The authors have recently drawn attention to the importance of angiotropism as a biologic phenomenom and prognostic factor in melanoma and as a likely correlate of EVMM. In addition, recent experimental studies strongly suggest a correlation of angiotropism of melanoma cells with EVMM. These studies, including cocultures of melanoma cells with capillarylike structures in vitro and the growth of green fluorescent protein-labeled melanoma cells in the shell-less chick chorioallantoic membrane model, have demonstrated the migration of angiotropic melanoma cells along the vascular channels, supporting the concept of EVMM. The new field of EVMM reviewed in this paper may prove useful in elucidating the molecular interactions involved in melanoma metastasis.