Ultrastructural and immunohistochemical studies of the periendothelial matrix in human melanoma: evidence for an amorphous matrix containing laminin

L1CAM and laminin vascular network: Association with the high-risk replacement histopathologic growth pattern in uveal melanoma liver metastases

The replacement histopathologic growth pattern (rHGP) in melanoma liver metastases connotes an aggressive phenotype (vascular co-option; angiotropic extravascular migratory spread) and adverse prognosis. Herein, replacement and desmoplastic HGP (dHGP) were studied in uveal melanoma liver metastases (MUM). In particular, L1CAM and a "laminin vascular network" were detected at the advancing front of 14/20 cases (p = 0.014) and 16/20 cases (p = 6.4e-05) rHGPs, respectively, but both were absent in the dHGP (8/8 cases) (p = 0.014, and p = 6.3e-05, respectively). L1CAM highlighted progressive extension of angiotropic melanoma cells along sinusoidal vessels in a pericytic location (pericytic mimicry) into the hepatic parenchyma. An inverse relationship between L1CAM expression and melanin index (p = 0.012) suggested differentiation toward an amelanotic embryonic migratory phenotype in rHGP. Laminin labeled the basement membrane zone interposed between sinusoidal vascular channels and angiotropic melanoma cells at the advancing front. Other new findings: any percentage of rHGP and pure rHGP had a significant adverse effect on metastasis-specific overall survival (p = 0.038; p = 0.0064), as well as predominant rHGP (p = 0.0058). Pure rHGP also was associated with diminished metastasis-free survival relative to dHGP (p = 0.040), possibly having important implications for mechanisms of tumor spread. In conclusion, we report for the first time that L1CAM and a laminin vascular network are directly involved in this high-risk replacement phenotype. Further, this study provides more detailed information about the adverse prognostic effect of the rHGP in MUM.

Vessel co-option in cancer

All solid tumours require a vascular supply in order to progress. Although the ability to induce angiogenesis (new blood vessel growth) has long been regarded as essential to this purpose, thus far, anti-angiogenic therapies have shown only modest efficacy in patients. Importantly, overshadowed by the literature on tumour angiogenesis is a long-standing, but continually emerging, body of research indicating that tumours can grow instead by hijacking pre-existing blood vessels of the surrounding nonmalignant tissue. This process, termed vessel co-option, is a frequently overlooked mechanism of tumour vascularization that can influence disease progression, metastasis and response to treatment. In this Review, we describe the evidence that tumours located at numerous anatomical sites can exploit vessel co-option. We also discuss the proposed molecular mechanisms involved and the multifaceted implications of vessel co-option for patient outcomes.

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.

Angiotropism in primary cutaneous melanoma is associated with disease progression and distant metastases: A retrospective study of 179 cases

BACKGROUND

Angiotropism is the histopathological correlate of pericytic mimicry and extravascular migratory metastasis (EVMM), a mechanism of melanoma spread by migration along the external surface of blood and lymphatic vessels. The frequency of angiotropism in primary cutaneous melanoma and the clinical utility of its detection remain unclear.

METHODS

We investigated angiotropism in 179 primary cutaneous melanomas by hematoxylin and eosin (H&E), CD31, and S100/D240 stains.

RESULTS

We detected angiotropism in 31 cases (17%) by H&E. CD31 immunohistochemistry increased detection to 59 cases (33%). When lymphatic vessels were included by using S100/D240 stains, 67 cases (37%) cases were positive. Angiotropism was associated with lymphatic invasion and mitotic rate with all detection methods. There was an association with increased tumor thickness when detected by H&E and CD31. No association with sentinel lymph node status was seen. By H&E and CD31 staining, angiotropism was associated with disease progression and distant metastases by univariate, but not multivariate analysis. Overall survival was not affected by the presence of angiotropism.

CONCLUSIONS

Angiotropism is relatively common in primary melanoma when immunohistochemical stains are used for detection and associated with mitotic rate and intravascular lymphatic invasion. The association with disease progression and distant metastasis suggests that it represents an alternative pathway of metastasis, that is, EVMM/pericytic mimicry vs intravascular spread.

Replacement and desmoplastic histopathological growth patterns: A pilot study of prediction of outcome in patients with uveal melanoma liver metastases

Up to 50% of uveal melanomas (UM) metastasise to the liver within 10 years of diagnosis, and these almost always prove rapidly fatal. As histopathological growth patterns (HGPs) of liver metastases of the replacement and desmoplastic type, particularly from colon and breast carcinoma, may import valuable biological and prognostic information, we have studied HGP in a series of 41 UM liver metastases originating from 41 patients from the period 2006–2017. Twenty patients underwent enucleation while 21 had radiation therapy. Analysis of UM by array comparative genomic hybridisation revealed: 25 (64%) patients with high risk (monosomy3/8q gain); 13 (33%) intermediate risk (M3/8normal or disomy3/8q gain); and 1 low risk (disomy3/8normal). The principal HGP was replacement in 30 (73%) cases and desmoplastic in 11 (27%) cases. Cases with replacement demonstrated striking vascular co‐option/angiotropism. With the development of liver metastasis, only the replacement pattern, largest primary tumour diameter, and R2 (incomplete resection) status predicted diminished overall survival (OS; p < 0.041, p < 0.017, p < 0.047, respectively). On multivariate analysis, only HGP (hazard ratio; HR = 6.51, p = 0.008) and resection status remained significant. The genomic high‐risk variable had no prognostic value at this stage of liver metastasis. Chi‐square test showed no association of HGP with monosomy 3 or 8q gain. Eighteen of 41 (44%) patients are alive with disease and 23 (56%) patients died with follow‐up ranging from 12 to 318 months (mean: 70 months, median: 47 months). In conclusion, we report for the first time the frequency of the replacement and desmoplastic HGPs in liver UM metastases resected from living patients, and their potential important prognostic value for UM patients, as in other solid cancers. These results may potentially be utilised to develop radiological correlates and therapeutic targets for following and treating patients with UM metastases.

Lymphatic invasion and angiotropism in primary cutaneous melanoma

Access of melanoma cells to the cutaneous vasculature either via lymphatic invasion or angiotropism is a proposed mechanism for metastasis. Lymphatic invasion is believed to be a mechanism by which melanoma cells can disseminate to regional lymph nodes and to distant sites and may be predictive of adverse outcomes. Although it can be detected on hematoxylin- and eosin-stained sections, sensitivity is markedly improved by immunohistochemistry for lymphatic endothelial cells. Multiple studies have reported a significant association between the presence of lymphatic invasion and sentinel lymph node metastasis and survival. More recently, extravascular migratory metastasis has been suggested as another means by which melanoma cells can spread. Angiotropism, the histopathologic correlate of extravascular migratory metastasis, has also been associated with melanoma metastasis and disease recurrence. Although lymphatic invasion and angiotropism are not currently part of routine melanoma reporting, the detection of these attributes using ancillary immunohistochemical stains may be useful in therapeutic planning for patients with melanoma.

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.

Malignant melanoma and its stromal nonimmune microecosystem

In recent years, rapid advances were reached in the understanding of a series of biologic signals influencing cutaneous malignant melanoma (CMM) cells. CMM is in close contact with a peculiar dermal extracellular matrix (ECM). Stromal cells store and release various structural ECM components. The impact on CMM growth and progression is mediated through strong and long-lasting effects of ECM products. This paper summarizes some peculiar aspects of the peri-CMM stroma showing intracytoplasmic loads in Factor XIIIa, CD34, versican, and α (IV) collagen chains. The restricted peri-CMM skin territory exhibiting such changes corresponds to the area showing neoangiogenesis and extravascular unicellular metastatic spread. The latter inconspicuous migratory CMM cells possibly correspond to CMM stem cells or to CMM cells with aberrant HOX gene expression. Their presence is associated with an increased risk for metastases in the regional sentinel lymph nodes. In conclusion, the CMM-stroma connection appears crucial to the growth regulation, invasiveness and initial metastatic spread of CMM cells. Although much remains to be learned in this field, the active intervention of the peri-CMM stroma is likely involved in the inconspicuous early metastatic migration of CMM cells.

Angiotropic metastatic malignant melanoma in a canine mammary gland

An eleven-year-old spayed female Yorkshire Terrier presented with a sublumbar mass and upon ultrasonographic examination, was revealed to have a mammary gland tumor. Black to reddish colored masses, located in the visceral peritoneum of the sublumbar region was observed on laparotomy with masectomy of the right side. In the laparotomy, we observed reddish masses multifocally located in the serosal membrane of the large intestine. Histopathologic examination of the intestinal and abdominal mass showed highly invasiveness into the muscle and metastasis of melanocytic tumor cells through the blood vessels. The mammary glands showed abnormal hyperplasia of melanocytes, destruction of the normal glands by tumor cells and infiltration of some lymphocytes in the pool of melanocytic cells. We have identified a malignant melanoma containing an angiotumoral complex in which tumor cells occupied a pericytic location along the microvessels with intravasation determined by immunohistochemistry for S100 protein and protein kinase C-α. Histologic findings in this dog lead to a diagnosis of an angiotropic metastatic malignant melanoma.

Thigmotropism of malignant melanoma cells

During malignant melanoma (MM) progression including incipient metastasis, neoplastic cells follow some specific migration paths inside the skin. In particular, they progress along the dermoepidermal basement membrane, the hair follicles, the sweat gland apparatus, nerves, and the near perivascular space. These features evoke the thigmotropism phenomenon defined as a contact-sensing growth of cells. This process is likely connected to modulation in cell tensegrity (control of the cell shape). These specifically located paucicellular aggregates of MM cells do not appear to be involved in the tumorigenic growth phase, but rather they participate in the so-called "accretive" growth model. These MM cell collections are often part of the primary neoplasm, but they may, however, correspond to MM micrometastases and predict further local overt metastasis spread.

'Malignant melanoma microecosystem': Immunohistopathological insights into the stromal cell phenotype

Cutaneous malignant melanoma (MM) is rooted in the dermal connective tissue, which consists of apparently unremarkable stromal cells as they appear upon regular histopathological examination. However, a number of in vitro studies have shown that these cells produce diverse types of cytokines, growth factors and enzymes in excess. In addition, they store and probably release various structural components of the extracellular matrix (ECM). Most of the current information comes from in vitro experiments, and these findings do not always correlate with investigations carried out using excised human MM tissue. The MM-stroma connection appears crucial to the regulation of neoplastic growth, invasiveness and initial metastatic spread. However, little is known about the in vivo intracellular storage and extracellular deposits of specific ECM macromolecules located inside and around MM lesions. This review summarizes various distinct features of the peri-MM stroma, which shows an intracytoplasmic abundance of Factor XIIIa, versican and various α (IV) collagen chains. The area exhibiting such changes corresponds to the location where neoangiogenesis commonly develops and where extravascular unicellular metastatic MM lesions are possibly found. Some of these inconspicuous migratory malignant melanocytes may actually correspond to MM stem cells. Their presence was found to be significantly associated with an increased risk for distant metastases, particularly in the sentinel lymph nodes. Although much remains to be learned, active intervention of the ECM appears likely in the inconspicuous early dermal metastatic migration of MM cells.

Melanoma prognostic factors found in the dermatopathology report

Significant prognostic information is available in a routine melanoma dermatopathology report. Features that are enumerated in the pathology report and that portend a potentially poorer prognosis are older age, site (acral, head, neck), male sex, increasing Breslow tumor thickness, increasing Clark's level, ulceration, increasing number of mitoses, vertical growth phase, regression, absence of a host inflammatory response, increased tumor vascularity, angiotropism, vascular invasion, neurotropism, marked atypia, and satellite metastasis.

Integrin agonists as adjuvants in chemotherapy for melanoma

PURPOSE

Metastatic melanomas are generally resistant to chemotherapy and radiation, even when wild-type for p53. These tumors often grow in small nests where many of the cells have little contact with extracellular matrix (ECM). Previous work showed that M21 melanomas undergo apoptosis in response to chemotherapy when cells are adherent to ECM but not in suspension. Thus, reduced integrin-dependent adhesion to ECM could mediate therapy resistance. The goal of this study was to test whether stimulation of integrin signaling could increase chemotherapeutic efficacy.

EXPERIMENTAL DESIGN

Colony forming assays and survival assays were used to test the responses of melanoma lines in vitro. Severe combined immunodeficient mice with subcutaneous human melanomas received chemotherapy with or without reagents that stimulate integrin signaling; tumor volume was then monitored over time.

RESULTS

Clonal growth assays confirmed that M21 cells showed reduced sensitivity to the chemotherapeutic drug 1-beta-D-arabinofuranosylcytosine (araC). When five additional primary melanoma lines were screened, 80% showed higher sensitivity when adherent compared with suspended. Subcutaneous M21 tumors in vivo showed minimal ECM between tumor cells. To evaluate the importance of integrin signaling in chemoresistance in this model, mice were treated with araC, with or without the multivalent snake venom disintegrin contortrostatin or the activating anti-beta1 integrin antibody TS2/16. Although araC, TS2/16, or contortrostatin alone had little effect on M21 tumor growth, combining araC with either integrin signaling reagents strongly reduced growth (P = 0001).

CONCLUSIONS

Loss of integrin-mediated adhesion is rate limiting for therapeutic response in this model. Combining chemotherapy with reagents that stimulate integrin signaling may therefore provide a new approach to therapy.

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.

The molecular basis of melanomagenesis and the metastatic phenotype

The last two decades have seen spectacular advances in our understanding of the biology of melanoma and, in particular, have elucidated the mechanisms operative in disease initiation and progression. With respect to the former, the genetics of melanoma and in particular the impact of genetic defects on dysregulation of the cell cycle are key issues in malignant transformation and are a major focus of this review. With respect to the latter, consideration also is given to the acquisition of growth factor autonomy and the capacity for invasion and metastasis from the standpoint of cell adhesion, motility, and matrix digestion. These events have specific morphologic correlates that will be briefly addressed. Where relevant, we will address certain of the modern pharmacogenetic strategies that flow from these novel observations concerning melanoma biology.

C16 laminin peptide increases angiotropic extravascular migration of human melanoma cells in a shell-less chick chorioallantoic membrane assay

BACKGROUND

As distinct from intravascular dissemination, extravascular migratory metastasis (EVMM) has been described as a potential additional mechanism of melanoma spread in which tumour cells migrate along the external surfaces of vessels. Recent experimental studies strongly suggest a correlation of angiotropism of melanoma cells with EVMM. Angiotropic melanoma cells are linked to the endothelium by an amorphous matrix confirmed to contain laminin.

OBJECTIVES

To investigate whether laminin plays a role in this extravascular mechanism of tumour spread.

METHODS

We tested the effect of the C16 laminin peptide on melanoma spread in a shell-less chick chorioallantoic membrane model.

RESULTS

After 3 days, green fluorescent protein-expressing melanoma cells were observed spreading along or in the immediate proximity of vessels. The C16 laminin peptide significantly lengthened the distance of extravascular, angiotropic migration of melanoma cells. Histopathology confirmed the angiotropism of melanoma cells without intravasation, compatible with that observed with human angiotropic melanoma.

CONCLUSIONS

The results of this study suggest that the C16 laminin gamma1 chain peptide has angiotropic, extravascular migration-promoting activity on human melanoma cells, and might be a molecular target for preventing melanoma metastasis.

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.

Angiotropism in Epidermotropic Metastatic Melanoma

The diagnosis of epidermotropic metastatic malignant melanoma (EMMM) can be extremely challenging for both clinicians and pathologists. The diffculties include distinguishing metastatic lesions with an epidermal component from residual incompletely excised primary melanoma, and multiple primary melanomas. This has great prognostic significance as the current American Joint Committee on Cancer guidelines consider localized metastatic disease such as satellites and intransits in the nodal (N) category of N2C or stage IIIB disease. In this report, we present a case of EMMM with angiotropism. Additionally, we discuss in detail the differential diagnosis for recurrence of malignant melanoma with an epidermal component within the scar. Angiotropism may be seen in lesions of EMMM and the current literature suggests that angiotropism is highly suggestive of metastatic melanoma. The differential diagnosis of locally recurrent melanoma with an epidermal component can be extremely challenging and the presence of angiotropism may be a clue to the diagnosis of EMMM.

Covalent modification of porous implants using extracellular matrix proteins to accelerate neovascularization

Healing associated with many polymeric biomedical implants commonly involves the formation of an avascular fibrous capsule. The lack of either formation or persistence of blood vessels in formed fibrous capsules, as well as a lack of new blood vessels within porous polymeric implants, often results in poor performance of the implant. The current study evaluated the use of extracellular matrix protein modification of a commonly used biomedical implant material, expanded polytetrafluoroethylene (ePTFE), as a mechanism to increase the neovascularization both within these porous implants and in tissue that forms in the peri-implant area. Discs of ePTFE were covalently modified with different extracellular matrix proteins including collagen type IV, fibronectin, and laminin type I. Discs were implanted into the adipose tissue of adult rats, and following a 5-week implant phase, histologic analysis of peri-implant tissue angiogenesis and implant neovascularization was performed. Striking differences were observed in angiogenic and neovascularization responses to matrix-modified ePTFE when compared with control, untreated ePTFE. Fibronectin treatment resulted in an extensive inflammatory response but, relative to the degree of inflammation, limited evidence of tissue angiogenesis or polymer neovascularization. Collagen type IV treatment groups exhibited a significant increase in angiogenesis in the peri-implant tissue with minimal evidence of implant neovascularization. In contrast to all other implant modifications, laminin type 1-treated ePTFE samples stimulated an extensive peri-implant tissue angiogenic response and a coordinate neovascularization of the porous interstices of the biomaterial.

Angiotropism of Human Melanoma: Studies Involving In Transit and Other Cutaneous Metastases and the Chicken Chorioallantoic Membrane

Melanoma cell migration along the outside of vessels has been termed "extravascular migratory metastasis" (EVMM), as distinct from intravascular dissemination. Previous studies in both human and experimental melanoma models have shown angiotropism of melanoma cells, suggesting EVMM. Our objectives are to study the mechanism of dissemination of human melanoma cells in the chick chorioallantoic membrane (CAM) and to compare the histopathology in the CAM with that of patients with in transit and other cutaneous melanoma metastases. Human and murine melanoma cells were inoculated onto the CAM and observed over a 10-day period for tumor dissemination. Both human melanoma specimens from 26 patients and melanoma cells growing on the CAM showed the presence of tumor cell angiotropism at the invasive front of the tumor and at some distance from the tumor mass. In addition, a clear progression of melanoma cells spreading on the CAM was observed along the abluminal surface of vessels, where they occupied a perivascular location. By day 10 after injection, small micrometastases had developed along vessels, in a pattern similar to that in transit and other cutaneous melanoma metastases. In addition, the results suggested that the number of micrometastases directly correlated with increasing tumor volume. Taken together, these data suggest that the CAM is a relevant model for studying tumor cell dissemination, and that EVMM may be a mechanism by which some melanoma cells spread to nearby and even distant sites.

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

OBJECTIVES

To report several samples of invasive human prostate cancer showing angiotropism, and to use human prostate cancer cells stably expressing green fluorescence protein (GFP) in in vitro and in vivo models to assess the dissemination pathway of prostate cancer cells.

MATERIALS AND METHODS

Malignant melanoma and prostate carcinoma cells can migrate along anatomical structures such as nerves; previous studies showed that melanoma cells can be perivascular, on the outside of the endothelium, i.e. they are angiotropic, which suggests the hypothesis that melanoma cells also may migrate along vascular channels, termed 'extravascular migratory metastasis' (EVMM). Thus we examined histologically 10 human prostatic carcinoma specimens for the presence of angiotropism. In vitro, the PC-3 prostate cancer cells were co-cultures with capillary-like structures. In vivo, PC-3 cells were implanted on the chick chorio-allantoic membrane (CAM).

RESULTS

Histologically, in all 10 cases, angiotropism was detected at least focally within the tumour or at the advancing front of the tumour. In vitro, the PC-3 cells spread along the external surface of the vascular tubules; in vivo, PC-3 cells formed a cuff around some vessels a few millimetres beyond the tumour, showing angiotropism. Histopathology of the CAM confirmed the perivascular location of tumour cells and the absence of tumour cells within the vessel lumina.

CONCLUSION

The presence of angiotropic tumour cells in human invasive prostate cancers, associated with the angiotropism of GFP prostate cancer cells cultivated in vitro and in vivo in angiogenic models, raises the possibility that some prostate tumour cells may migrate along the external surface of vessels as a mechanism of spread, i.e. EVMM.

Angiotropic malignant melanoma and extravascular migratory metastasis: description of 36 cases with emphasis on a new mechanism of tumour spread

AIMS

We have identified in malignant melanoma an angio-tumoural complex in which tumour cells occupy a pericytic location along the endothelium of microvessels without evidence of intravasation. This pericytic angiotropism of melanoma cells, without any sign of intravasation, suggests that melanoma cells may migrate along the external surface of vessels, a mechanism we have termed 'extravascular migratory metastasis' (EVMM), as distinct from intravascular dissemination.

METHODS

The present study describes, for the first time, a series of 36 invasive melanoma cases ascertained for the presence of the histopathological characteristic of angiotropism.

RESULTS

All cutaneous melanomas (31/35) were level IV with the exception that two melanomas were level II and two level V. In all cases, angiotropism was easily observed at the advancing front of the tumour or in nearby tissue.

CONCLUSIONS

The study demonstrates that angiotropism of melanoma cells can be easily detected microscopically in routine tissue sections, i.e., in close proximity to microvessels (in a pericytic location). This phenomenon may prove to be important both biologically and prognostically in the routine histopathological assessment of melanoma, since we have recently shown that angiotropism could be a prognostic factor predicting risk for metastasis of melanoma. Our continued investigations to elucidate the significance of angiotropism in melanoma may help in understanding the molecular basis of metastasis and EVMM.

Pericyte-like location of GFP-tagged melanoma cells: ex vivo and in vivo studies of extravascular migratory metastasis

Previous studies have demonstrated that some tumor cells occupy a pericyte-like location in melanoma, forming angio-tumoral complexes. We hypothesized that these tumor cells are migrating along the abluminal surface of the endothelium, a mechanism termed "extravascular migratory metastasis." In the present study, we have used human and murine melanoma cells that stably express enhanced green fluorescence protein (GFP) to examine, in an ex vivo co-culture model, melanoma cell interactions with vessels that have sprouted from rat aortic rings. We also used in vivo tumor growth on the chick chorioallantoic membrane (CAM) to observe the dissemination pathway of melanoma cells. In the ex vivo rat aorta system, we observed a pericyte-like location of tumor cells that were spreading along the vascular channels. For examination of the CAM in vivo, we have used the Lugassy preparation, allowing one to obtain striking images of the relationship between fluorescent GFP cells and microvessels. Melanoma cells were found cuffing the outside of vessels around the tumor. Tumor cells were observed along the vessels several centimeters from the tumor. Confocal microscopy and histopathology confirmed the pericyte-like location of tumor cells, without any observable intravasation. The results indicate that melanoma cells can migrate along the abluminal surface of vessels. This study also demonstrates that these models can provide quantitation analysis that may prove useful in elucidating the molecular interactions involved in extravascular migratory metastasis.

Pericytic-like angiotropism of glioma and melanoma cells

We have identified in malignant melanoma an angiotumoral complex in which tumor cells occupy a pericytic location along the endothelium of microvessels without evidence of intravasation. We have suggested that this pericytic-like angiotropism could be a marker of an extravascular migration of tumor cells along the abluminal surface of vessels. The extravascular migratory metastasis proposed for melanoma has close analogies with glioma migration. To compare our hypothesis of extravascular migration by melanoma with the migration of glioma cells, we have used the B16 murine melanoma cell line and the GL26 murine glioma cell line in an in vivo murine brain tumor model and in vitro using endothelial cells that have formed capillary-like structures and have been cocultivated with tumor cells. In the brain tumors, a clear progression of glioma and melanoma cells was observed along the abluminal surface of vessels, where they occupied a pericytic location along the periendothelial laminin. In vitro, time-lapse videomicroscopy recorded the migration of tumor cells toward endothelial tubules. After 24 hours, both the melanoma cells and the glioma cells were localized along the external surfaces of the vascular tubules, occupying a pericytic-like location. These similarities between glioma and melanoma support the hypothesis of an extravascular migration of melanoma cells, particularly along the abluminal surface of vessels.

PAS-positive loops and networks as a prognostic indicator in cutaneous malignant melanoma

Recently, microvascular channels, as detected by PAS histochemistry, were positively correlated with poor prognosis in uveal malignant melanoma. Since uveal melanomas are not penetrated by lymphatic vessels, while cutaneous melanomas are, the question arises as to whether these loops and networks are also of prognostic relevance in cutaneous melanoma. Histochemically and immunohistochemically detected loops and networks in 100 cases of cutaneous malignant melanoma were correlated with the occurrence of metastasis in a 10-year follow-up study. To detect these patterns, the significance of various methods (PAS reaction with/without nuclear counterstain, anti-laminin immunohistochemistry) was investigated. The presence of loops and networks was a highly significant prognostic marker (p<0.0001) for metastasis in cutaneous malignant melanoma. The presence of these patterns proved to have higher prognostic relevance for metastasis than Breslow's tumour thickness, especially for stage IB and stage IIA tumours (intermediate thickness/risk). PAS reaction without nuclear counterstain proved to be the best method to detect these patterns. Compared with the conventional staging of Breslow's tumour thickness, and especially so for stage IB and IIA melanomas, the determination of PAS-positive loops and networks in cutaneous malignant melanoma provides additional prognostic information.

Tumor microvessels in melanoma express the beta-2 chain of laminin. Implications for melanoma metastasis

The ultrastructural localization of an amorphous matrix to the interface between microvessel endothelium and tumor cells has been recently reported in a series of melanomas. Laminin expression as documented by immunohistochemistry was localized to microvessels in melanomas showing the amorphous matrix. In order to identify more precisely the type of laminin present in this amorphous material, immunostaining was carried out on cryostat sections from 16 human melanoma specimens. Four murine monoclonal antibodies directed against the alpha-3, beta-2, beta-3 and gamma-2 laminin chains were employed. In the melanomas studied, alpha3, beta3 and gamma2 laminin chains showed only minimal focal vascular positivity. In contrast, the beta2 (16/16 cases) laminin chain exhibited a consistent positivity in an angiocentric pattern about tumor microvessels. In all melanomas, some tumor cells seemed to spread along the abluminal surface of the small vessels, exhibiting a pericytic location, particularly along the intratumoral projections formed by the beta2 laminin chain. Given the role of laminin in migration and tumor progression, the results suggest a role of the beta2 laminin chain in melanoma spread, promoting tumor migration along the abluminal surface of vessel, a phenomenon which has been termed extra-vascular migratory metastasis.