Evaluation of Immunohistochemical Markers of Lymphatic and Blood Vessels in Canine Mammary Tumours

Synovial myxoma or myxosarcoma? Lymph node metastasis in 2 dogs

Synovial myxoma, a rare joint tumor in dogs, has traditionally been considered benign, acknowledging that local invasion into regional tissues including bone may be present. Given the diagnostic challenges in distinguishing synovial myxoma from other joint lesions through clinical features and diagnostic imaging, definitive diagnosis relies on characteristic gross and histologic features. Within the inner surface of the joint capsule, synovial myxomas form nodules of stellate-to-spindle cells within abundant myxomatous matrix. We present here 2 cases of synovial myxoma with metastasis to regional lymph nodes and compare these 2 cases to 3 cases without evidence of lymph node metastasis. Aside from lymphovascular invasion in one case with metastasis, there were no overt histologic features of the primary tumor to suggest aggressive biologic behavior. The finding of lymph node metastasis warrants reconsideration of the term "synovial myxoma" for this neoplasm. We suggest the term "synovial myxosarcoma," considering that histologic features of the primary tumor do not predict biologic behavior. Our case series highlights the importance of lymph node sampling in suspected synovial myxosarcoma cases as well as thorough histologic examination, emphasizing careful evaluation for lymphovascular invasion.

International Guidelines for Veterinary Tumor Pathology: A Call to Action

Standardization of tumor assessment lays the foundation for validation of grading systems, permits reproducibility of oncologic studies among investigators, and increases confidence in the significance of study results. Currently, there is minimal methodological standardization for assessing tumors in veterinary medicine, with few attempts to validate published protocols and grading schemes. The current article attempts to address these shortcomings by providing standard guidelines for tumor assessment parameters and protocols for evaluating specific tumor types. More detailed information is available in the Supplemental Files, the intention of which is 2-fold: publication as part of this commentary, but more importantly, these will be available as "living documents" on a website (www.vetcancerprotocols.org), which will be updated as new information is presented in the peer-reviewed literature. Our hope is that veterinary pathologists will agree that this initiative is needed, and will contribute to and utilize this information for routine diagnostic work and oncologic studies. Journal editors and reviewers can utilize checklists to ensure publications include sufficient detail and standardized methods of tumor assessment. To maintain the relevance of the guidelines and protocols, it is critical that the information is periodically updated and revised as new studies are published and validated with the intent of providing a repository of this information. Our hope is that this initiative (a continuation of efforts published in this journal in 2011) will facilitate collaboration and reproducibility between pathologists and institutions, increase case numbers, and strengthen clinical research findings, thus ensuring continued progress in veterinary oncologic pathology and improving patient care.

Pilot study supporting the existence of novel lymphatic channels within the canine anterior uveal tract using Lyve-1 and CD31

OBJECTIVE

To demonstrate the existence of lymphatics in the canine anterior uvea using lymphatic-specific markers Lyve-1, Prox-1, and podoplanin, the endothelial cell marker CD31, and basement membrane matrix marker collagen IV.

DESIGN

Prospective Study.

ANIMALS

Eight normal globes from animals euthanized for unrelated health problems.

PROCEDURES

Sagittally cut serial sections of six normal canine eyes were immunofluorescence double-stained with Lyve-1 and CD31 and single-stained with colorimetric Prox-1 and collagen IV. Three serial sections from 2 additional eyes were cut in the coronal plane at the level of the ciliary body and immunofluorescence double-stained with Lyve-1 and CD31 to map lymphatic channel distribution. Lymphatics from normal canine lymph nodes were used for validation of podoplanin.

RESULTS

Four of 6 of the sagitally sectioned eyes had Lyve-1-positive lymphatic-like structures that were distinct from CD31-positive blood vessels in the iris base and ciliary body. Both of the coronally sectioned globes had Lyve-1-positive lymphatic-like structures in the ciliary body. The location of these structures was evaluated and found to be diffusely present circumferentially around the ciliary body.

CONCLUSION AND CLINICAL RELEVANCE

These results support the existence of lymphatic channels in the anterior uveal tract of the canine eye. This could indicate the presence of a novel uveolymphatic outflow pathway, which may play a role in aqueous humor outflow. Future studies are needed to confirm the existence and elucidate the role of this proposed uveolymphatic outflow pathway and potentially develop novel treatment options for managing glaucoma.

Primary Lymphangiosarcoma of the Urinary Bladder in a Dog

Abdominal ultrasonographical and computed tomography examinations of a 12-year-old neutered female toy poodle revealed a protruding mass, approximately 2 cm in diameter, at the apex of the bladder. The mass was firm and haemorrhagic with a homogeneously brownish-yellow cut surface. Microscopically, it was unencapsulated and located in the muscle layer with invasion of the extra-muscular layer. It was composed of spindloid to oval neoplastic cells that formed irregular clefts and diffuse sheets that dissected bundles of collagen. Immunohistochemically, the neoplastic cells were positive for vimentin and lymphatic vessel endothelial hyaluronan receptor 1 antigens, but negative for cytokeratin AE1/AE3, factor VIII-related antigen, CD31, CD34, Prox-1, S100, desmin, α-smooth muscle actin and MyoD1. Negative immunolabelling for laminin antigen supported the absence of evidence of a basal lamina on ultrastructural examination. Based on these findings, this tumour was identified as a lymphangiosarcoma. To the best of our knowledge, this case is the first report of lymphangiosarcoma arising from the bladder in a dog.

Primary Cystic Lymphangioma of the Spleen in an Adult Dog

Proliferative disorders of lymphatic origin in animals are mostly congenital or occur within the first few months of life. Involvement of internal organs is extremely infrequent. A seven-year-old entire female mixed-breed dog was presented with apathy and poor appetite. Abdominal ultrasonography revealed a focally enlarged spleen with an anechoic round lesion. Splenectomy was performed and pathological examination demonstrated a sponge-like, compressible tumour composed of endothelium-lined vascular cystic spaces filled with eosinophilic proteinaceous material lacking erythrocytes. Immunohistochemical stains showed that cyst-lining cells were strongly positive for CD31 and factor VIII and focally positive for lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1). Based on these findings, the lesion was identified as splenic cystic lymphangioma. To the best of our knowledge, this is the first description of solitary lymphangioma of the spleen in animals.

Expression of Podoplanin in Mammary Cancers in Female Dogs

BACKGROUND/AIM

Mammary neoplasms are very common tumours in female dogs. Cancer-associated fibroblasts (CAFs) play an important role in the oncogenesis process. One of the useful proteins used in the diagnostics of CAFs cells is podoplanin (PDPN). The aim of our study was to assess the expression of PDPN in mammary cancer in female dogs.

MATERIALS AND METHODS

Our study cohort included 61 cancers and 21 adenomas of the mammary tumour in bitches. Expression of podoplanin, Ki-67 and HER2 was determined using the Immunohistochemical (IHC) method. PDPN expression at the mRNA level was determined using real-time PCR.

RESULTS

Expression of PDPN in CAFs was observed in 22.9% of cases of mammary cancers in bitches, with no PDPN expression in adenomas. A positive correlation was found between the expression of PDPN in CAFs and the grade of histological malignancy and expression of Ki-67.

CONCLUSION

PDPN plays a significant role during the process of carcinogenesis of mammary tumours in female dogs.

Comparative Approach to the Temporo-Spatial Organization of the Tumor Microenvironment

The complex ecosystem in which tumor cells reside and interact, termed the tumor microenvironment (TME), encompasses all cells and components associated with a neoplasm that are not transformed cells. Interactions between tumor cells and the TME are complex and fluid, with each facet coercing the other, largely, into promoting tumor progression. While the TME in humans is relatively well-described, a compilation and comparison of the TME in our canine counterparts has not yet been described. As is the case in humans, dog tumors exhibit greater heterogeneity than what is appreciated in laboratory animal models, although the current level of knowledge on similarities and differences in the TME between dogs and humans, and the practical implications of that information, require further investigation. This review summarizes some of the complexities of the human and mouse TME and interjects with what is known in the dog, relaying the information in the context of the temporo-spatial organization of the TME. To the authors' knowledge, the development of the TME over space and time has not been widely discussed, and a comprehensive review of the canine TME has not been done. The specific topics covered in this review include cellular invasion and interactions within the TME, metabolic derangements in the TME and vascular invasion, and the involvement of the TME in tumor spread and metastasis.

Comparative pathophysiology and management of protein-losing enteropathy

Protein‐losing enteropathy, or PLE, is not a disease but a syndrome that develops in numerous disease states of differing etiologies and often involving the lymphatic system, such as lymphangiectasia and lymphangitis in dogs. The pathophysiology of lymphatic disease is incompletely understood, and the disease is challenging to manage. Understanding of PLE mechanisms requires knowledge of lymphatic system structure and function, which are reviewed here. The mechanisms of enteric protein loss in PLE are identical in dogs and people, irrespective of the underlying cause. In people, PLE is usually associated with primary intestinal lymphangiectasia, suspected to arise from genetic susceptibility, or “idiopathic” lymphatic vascular obstruction. In dogs, PLE is most often a feature of inflammatory bowel disease (IBD), and less frequently intestinal lymphangiectasia, although it is not proven which process is the true driving defect. In cats, PLE is relatively rare. Review of the veterinary literature (1977‐2018) reveals that PLE was life‐ending in 54.2% of dogs compared to published disease‐associated deaths in IBD of <20%, implying that PLE is not merely a continuum of IBD spectrum pathophysiology. In people, diet is the cornerstone of management, whereas dogs are often treated with immunosuppression for causes of PLE including lymphangiectasia, lymphangitis, and crypt disease. Currently, however, there is no scientific, extrapolated, or evidence‐based support for an autoimmune or immune‐mediated mechanism. Moreover, people with PLE have disease‐associated loss of immune function, including lymphopenia, severe CD4+ T‐cell depletion, and negative vaccinal titers. Comparison of PLE in people and dogs is undertaken here, and theories in treatment of PLE are presented.

Small Intestinal Lymphatic Hypoplasia in Three Dogs with Clinical Signs of Protein-losing Enteropathy

Intestinal lymphatic hypoplasia (ILH) is a rare but well-documented cause of protein-losing enteropathy (PLE) in human infants. To our knowledge, this condition has not been reported previously in veterinary medicine. Here we report the clinical and histopathological findings in three dogs that presented with clinical signs of PLE. The onset of PLE was early in an 18-month-old Great Pyrenees, while the other two dogs, a pug and a Tibetan terrier, had a later onset at 4 and 12 years of age, respectively. The presence of intestinal lymphatic and blood vessels was assessed by immunohistochemistry for human prospero homeobox 1 (prox-1), a lymphatic endothelial nuclear transcription factor and human von Willebrand factor (vWf), a marker of vascular endothelial cells, respectively. Small intestinal specimens taken from each dog showed severe mucosal oedema with a lack of prox-1 labelling of villous lacteals, dilated and tortuous vWf immunoreactive villous arterial and capillary blood vessels, and variable lamina propria mixed inflammatory cell infiltrates. Other histological features of ILH included club-shaped villi that were lined by low cuboidal epithelium or epithelial cells with cytoplasmic pallor and microvacuolar change, extrusion zone epithelial inversion and thin and inconspicuous villous longitudinal smooth muscles. While ILH is an uncommon diagnosis, it should be considered as a differential in dogs with clinical signs of PLE. The cause of canine ILH is unknown; however, a congenital abnormality with early or late onset of clinical signs is suspected. Diagnosis of ILH can be challenging; however, immunohistochemical labelling of lymphatic endothelial cells with prox-1 is essential for making this diagnosis.

Plexiform Vasculopathy in Feline Cervical Lymph Nodes

Plexiform vasculopathy refers to an endothelial proliferative disorder affecting cervical or inguinal lymph nodes of cats. The cause of this disorder and the origin of the proliferating endothelial cells are still unknown. In 4 cats with a history of a slowly growing, well-demarcated, nonpainful mass adjacent to the thyroid gland, an enlarged dark brown to red lymph node was removed. Histologically, the lymph nodes showed severe loss of lymphoid tissue with accumulations of erythrocytes. In addition, networks of capillary structures with well-differentiated endothelial cells on a collagen-rich stroma were observed, consistent with benign plexiform vasculopathy. Immunohistochemistry revealed the expression of the vascular endothelial markers CD31 and factor VIII-related antigen. In addition, immunolabeling with a Prox-1 antibody indicated a lymphendothelial origin. With respect to our findings, a lymphendothelial origin has to be considered in cases of intranodal vascular neoplasms.

Selenium Induces an Anti-tumor Effect Via Inhibiting Intratumoral Angiogenesis in a Mouse Model of Transplanted Canine Mammary Tumor Cells

Selenium (Se) has been widely reported to possess anti-tumor effects. Angiogenesis is the formation of new blood vessels and is required to supply oxygen, nutrients, and growth factors for tumor growth, progression, and metastasis. To explore whether the anti-tumor effect of Se was associated with angiogenesis in vivo, we studied the effects of sodium selenite (Sel) and methylseleninic acid (MSA) on tumors induced by canine mammary tumor cells (CMT1211) in mice; cyclophosphamide (CTX) served as a positive control. The results showed that the Se content was significantly increased in the Sel and MSA groups. Se significantly inhibited the tumor weights and volumes. Large necrotic areas and scattered and abnormal small necrotic areas were observed in the Se treatment group. Immunofluorescence double staining showed a reduction in the microvessel density (MVD) and increment in the vessel maturation index (VMI) compared with the untreated control group. As expected, the protein and mRNA levels of the angiogenesis factors angiopoietin-2 (Ang-2), platelet-derived growth factor (PDGF), and vascular endothelial growth factor (VEGF) were decreased in the Se-treated tumors by IHC, as shown by western blotting and RT-QPCR. We also found that organic Se MSA provided stronger inhibition of tumor growth compared with inorganic sodium selenite (Sel). Altogether, our results indicated that Se exerted anti-tumor effects in vivo at least partially by inhibiting angiogenic factors.

Lymphangiosarcoma with systemic metastases in a Japanese domestic cat

A 4-year-2-month-old female Japanese domestic cat was diagnosed with lymphangiosarcoma through tissue biopsy of an amputated leg. Two months later, the cat was euthanized, and postmortem findings revealed edema, and bruising at the caudal region of the trunk, pulmonary hemorrhage, pulmonary nodules and mediastinal lymphadenopathy. Microscopically, neoplastic tissues were observed in the dermis and subcutis of the trunk, lung, mediastinal lymph nodes, diaphragm, omentum and mesentery. The tumor cells were spindle to polygonal-shaped with nuclear pleomorphism aligning along pre-existing collagen bundles and forming irregular vascular channels in which the erythrocytes were rarely observed. These cells were immunopositive for vimentin, von Willebrand factor and CD31. Based on the histopathological and immunohistochemical features, the neoplasia was diagnosed as lymphangiosarcoma with systemic metastases.

Angiogenesis in canine mammary tumours: a morphometric and prognostic study

Angiogenesis in canine mammary tumours (CMTs) has been described previously; however, only the intratumoural (IT) region has been studied and information on peritumoural (PT) angiogenesis is lacking. In this study, the blood vessel density (BVD), blood vessel perimeter (BVP) and blood vessel area (BVA) in IT and PT regions of 56 benign CMTs, 55 malignant CMTs and 13 samples of normal mammary gland tissue were analyzed. In addition, the blood endothelial cell proliferation (BECP) as an indicator of ongoing angiogenesis was investigated. The prognostic value of each parameter was also examined. Blood vessels and proliferating blood endothelial cells were present in IT and PT regions of both benign and malignant tumours. The vessels in the PT region had a significantly higher area and perimeter compared with those in the IT region. Malignant tumours showed significantly more vessels with a smaller total BVA and a higher BECP compared with benign tumours and control tissue. In the PT regions there was a significantly higher BVD, BVA and BVP compared with the vessels in control tissue. Only the IT and PT BVD and PT BECP in benign tumours allowed prediction of survival. The morphology of blood vessels in CMTs shows similarities with those in human breast cancer, which strengthens the case for the use of dogs with CMTs in comparative oncology trials.

EGFR and microvessel density in canine malignant mammary tumours

The epidermal growth factor receptor (EGFR) is a transmembrane tyrosine kinase receptor which has been shown to have an important role in human breast cancer. Its role appears to be associated with increased angiogenesis and metastasis. In order to clarify its role in canine mammary tumours (CMT), 61 malignant neoplasms were studied by using immunohistochemistry, comparing expression of EGFR, microvessel density (MVD) by CD31 immunolabelling and characteristics of tumour aggressiveness. High EGFR immunoexpression was statistically significantly associated with tumour size, tumour necrosis, mitotic grade, histological grade of malignancy and clinical stage. High CD31 immunoreactivity was statistically significantly associated with tubule formation, histological grade of malignancy and clinical stage. A positive correlation between EGFR and CD31 immunoexpression (r = 0.843; P < 0.001) was also observed. Results suggest that an over-expression of EGFR may contribute to increased angiogenesis and aggression in malignant CMT, presenting the possibility of using EGFR inhibitors in the context of metastatic disease treatment.