Basant H. Ahmed

The histologic and molecular heterogeneity of human muscle-invasive bladder cancer (MIBC) is a major contributor to poor treatment outcomes. While most cases of MIBC are diagnosed as conventional urothelial carcinoma (UC), there is growing recognition of histologic subtypes and divergent differentiation within conventional UC. This is clinically significant, as some require modification of therapy and some are associated with more aggressive behavior. Spontaneously occurring UC in dogs has been shown to exhibit histologic and molecular features that closely resemble those of human MIBC. In this study, we evaluated 31 canine UC tumor samples for histologic subtypes and divergent differentiation. Slides were reviewed by a human uropathologist and three board-certified veterinary pathologists and assessed for expression of uroplakin III and E-cadherin. All tumors were classified as high-grade UC. Fifteen cases were identified as conventional UC. Among the remainder, eight displayed glandular differentiation, four were classified as sarcomatoid UC, two showed squamous differentiation, and one case each was classified as large nested and tubular and microcystic subtypes. In summary, this study found a higher frequency of certain histologic subtypes and divergent differentiation in canine UC—particularly sarcomatoid UC and UC with glandular differentiation—compared to previous reports in both canine UC and human MIBC. Conclusion The relatively high prevalence of the sarcomatoid UC subtype in dogs observed in this study suggests that canine UC may serve as a valuable translational model for evaluating novel therapeutic agents, particularly for this rare and aggressive variant in humans.

Preclinical biomedical research is limited by the predictiveness of in vivo and in vitro models. While in vivo models offer the most complex system for experimentation, they are also limited by ethical, financial, and experimental constraints. In vitro models are simplified models that do not offer the same complexity as living animals but do offer financial affordability and more experimental freedom; therefore, they are commonly used. Traditional 2D cell lines cannot fully simulate the complexity of the epithelium of healthy organs and limit scientific progress. The One Health Initiative was established to consolidate human, animal, and environmental health while also tackling complex and multifactorial medical problems. Reverse translational research allows for the sharing of knowledge between clinical research in veterinary and human medicine. Recently, organoid technology has been developed to mimic the original organ’s epithelial microstructure and function more reliably. While human and murine organoids are available, numerous other organoids have been derived from traditional veterinary animals and exotic species in the last decade. With these additional organoid models, species previously excluded from in vitro research are becoming accessible, therefore unlocking potential translational and reverse translational applications of animals with unique adaptations that overcome common problems in veterinary and human medicine.

Background: Bladder cancer is a significant malignancy in humans and canines, with high death rates and devastating clinical symptoms. Despite significant advances in therapeutic management over the years, only a small fraction of bladder cancer patients respond to immunotherapies as a second line of treatment. Since immunotherapies act on various cellular and molecular targets in the bladder cancer tumour microenvironment (TME), a greater understanding of the various types of immune cells, immune checkpoint molecules and cytokines involved in antitumour immunity will help to improve the success rate of current and novel immunotherapies, therefore enhancing the patients quality of life. Accumulating evidence shows fundamental similarities between human and canine muscle‐invasive bladder cancer (MIBC) in their clinical, histological and molecular features.Aim: This review focuses on comparative aspects of MIBC in both species, highlighting the role that canines can play as a model for studying MIBC. Additionally, we discuss the various types of immune cells within bladder cancer TME that can influence the prognosis and response to immunotherapy and chemotherapy in both species.Conclusion: It remains challenging to recapitulate the heterogeneity and complexity of the bladder cancer tumour microenvironment using in vivo and in vitro models, such as zebrafish and 3D organoids models. Optimization of these techniques to create a more representative translational model has been facilitated through in vitro immune‐oncology cocultures, which are considered promising tools to help select the ideal individualized treatment options and predict disease prognosis.

This study aimed to assess the morphometry of enterocytes as well as the goblet cell-to-enterocyte ratio in different intestinal segments of dogs with chronic enteropathies (CE). Histopathological intestinal samples from 97 dogs were included in the study (19 healthy juveniles, 21 healthy adults, 24 dogs with protein-losing enteropathy (PLE), and 33 CE dogs without PLE). Healthy adult small intestinal enterocytes showed progressively reduced epithelial cell height in the aboral direction, while juvenile dogs showed progressively increased epithelial cell height in the aboral direction. CE dogs had increased epithelial cell height in the duodenum, while PLE dogs had decreased epithelial cell heights compared to healthy adult dogs. Both the CE and PLE dogs showed decreased enterocyte width in the duodenal segment, and the ileal and colonic enterocytes of CE dogs were narrower than those of healthy adult dogs. CE dogs had a lower goblet cell-to-enterocyte ratio in the colon segment compared to healthy dogs. This study provides valuable morphometric information on enterocytes during canine chronic enteropathies, highlighting significant morphological enterocyte alterations, particularly in the small intestine, as well as a reduced goblet cell-to-enterocyte ratio in the colon of CE cases compared to healthy adult dogs.