A Review on Mammary Tumors in Rabbits: Translation of Pathology into Medical Care

Neoplastic and non-neoplastic lesions in biopsy samples from pet rabbits in Hong Kong: a retrospective analysis, 2019-2022

Rabbits are popular pets in the urban environment of Hong Kong, ranking third behind cats and dogs. Here we describe the frequency of neoplastic and non-neoplastic lesions in biopsies from pet rabbits submitted to the CityU Veterinary Diagnostic Laboratory between 2019 and 2022, comprising 247 tissue samples from 243 rabbits collected by veterinarians in 19 veterinary clinics. Among the 243 rabbits, there were 128 females (65 spayed), 114 males (54 castrated); sex information was not provided for 1 rabbit. The rabbit breeds included 45 Lionhead, 35 Dwarf, 14 Lop, 11 Dwarf Lop, 5 French Lop, 3 Angora, 2 Dutch, 2 Holland Lop, and 1 each of Netherland Dwarf, Velveteen, Mini Lop, and New Zealand White. The mean ages of rabbits with neoplastic and non-neoplastic lesions were 7.1 and 5.7 y, respectively. The most common neoplastic lesions were adenocarcinoma (26.4%), trichoblastoma (21.4%), sarcoma (9.4%), and thymoma (8.2%). The most common non-neoplastic lesion was uterine cystic endometrial hyperplasia (14.8%), followed by dermal abscess formation in the ventral abdomen or skin of the head (12.5%). Although a broad spectrum of other lesions was described, our findings in biopsies from pet rabbits in Hong Kong are consistent with those in other jurisdictions.

Mammary and reproductive tract tumours and tumour-like lesions of 286 small pet mammals: a retrospective study

Small mammals are very popular companion animals, and the incidence of particular tumour types in these animals is the subject of extensive research. We carried out a retrospective and comparative analysis of the incidence of reproductive tract and mammary tumours and tumour-like lesions collected from 103 pet rabbits, 75 pet rats, 71 guinea pigs, 12 mice, 11 hamsters, eight African pygmy hedgehogs, four ferrets and two chinchillas. The results indicate that uterine tumours and tumour-like lesions are common in pet rabbits, guinea pigs and African pygmy hedgehogs. In pet rabbits, the most common uterine tumour was endometrial adenocarcinoma, while in guinea pigs benign lesions predominated (ie, leiomyoma, endometrial adenoma, cystic endometrial hyperplasia and deciduoma). Uterine tumours in African pygmy hedgehogs included adenosarcomas and endometrial polyps. Ovarian lesions were found only in guinea pigs (ovarian rete adenomas, rete cysts) and African pygmy hedgehogs (mostly granulosa cell tumours), while testicular tumours were diagnosed in pet rabbits, one pet rat and one guinea pig. Mammary tumours were common in pet rabbits, pet rats, guinea pigs, mice, hamsters and African pygmy hedgehogs. In pet rats, the most common mammary tumour was fibroadenoma, while in other animals carcinomas predominated. In guinea pigs and, to a lesser extent, in pet rats, a significant percentage of mammary tumours occurred in males. Guinea pigs seem to be predisposed to mammary tumours of ductal origin. This study describes for the first time uterine angioleiomyoma in the pet rabbit and mammary spindle cell carcinoma in the Djungarian hamster and chinchilla.

Immunohistochemical Detection of Indoleamine 2,3-Dioxygenase in Spontaneous Mammary Carcinomas of 96 Pet Rabbits

For mammary carcinomas in pet rabbits, prognostic biomarkers are poorly defined, and treatment is limited to surgical excision. Additional treatment options are needed for rabbit patients for which surgery is not a suitable option. In human breast cancer, the immunosuppressive enzyme indoleamine 2,3-dioxygenase 1 (IDO1) represents a prognostic biomarker and possible therapeutic target. This retrospective immunohistochemical study examined IDO1 in 96 pet rabbit mammary carcinomas with known mitotic count, hormone receptor status, and percentage of stromal tumor infiltrating lymphocytes (TILs). Tumors were obtained from 96 pet rabbits with an average of 5.5 years. All rabbits with reported sex (n = 88) were female or female-spayed. Of the carcinomas, 94% expressed IDO1, and 86% had sparse TILs consistent with cold tumors. Statistically significant correlations existed between a higher percentage of IDO1-positive tumor cells, lower mitotic counts, and increased estrogen receptor expression. The threshold for significance was IDO1 staining in >10% of tumor cells. These results lead to the assumption that IDO1 expression contributes to tumorigenesis and may represent a prognostic biomarker and possible therapeutic target also in pet rabbit mammary carcinomas. They also support the value of rabbits for breast cancer research.

Tantalum oxide nanoparticles as versatile and high-resolution X-ray contrast agent for intraductal image-guided ablative procedure in rodent models of breast cancer

There are limited options for primary prevention of breast cancer (BC). Experimental procedures to locally prevent BC have shown therapeutic efficacy in animal models. To determine the suitability of FDA-approved iodine-containing and various metal-containing (bismuth, gold, iodine, or tantalum) preclinical nanoparticle-based contrast agents for image-guided intraductal (ID) ablative treatment of BC in rodent models, we performed a prospective longitudinal study to determine the imaging performance, local retention and systemic clearance, safety profile, and compatibility with ablative solution of each contrast agent. At least six abdominal mammary glands (>3 female FVB/JN mice and/or Sprague-Dawley rats, 10-11 weeks of age) were intraductally injected with commercially available contrast agents (Omnipaque® 300, Fenestra® VC, MVivoTM Au, MVivoTM BIS) or in-house synthesized tantalum oxide (TaOx) nanoparticles. Contrast agents were administered at stock concentration or diluted in 70% ethanol (EtOH) and up to 1% ethyl cellulose (EC) as gelling agent to assess their compatibility with our image-guided ablative procedure. Mammary glands were serially imaged by microCT for up to 60 days after ID delivery. Imaging data were analyzed by radiologists and deep learning to measure in vivo signal disappearance of contrast agents. Mammary glands and major organs were ultimately collected for histopathological examination. TaOx-containing solutions provided best imaging performance for nitid visualization of ductal tree immediately after infusion, low outward diffusion (<1 day) and high homogeneity. Of all nanoparticles, TaOx had the highest local clearance rate (46% signal decay as stock and 36% as ablative solution 3 days after ID injection) and exhibited low toxicity. TaOx-containing ablative solution with 1% EC caused same percentage of epithelial cell death (88.62% ± 7.70% vs. 76.38% ± 9.99%, p value = 0.089) with similar minimal collateral damage (21.56 ± 5.28% vs. 21.50% ± 7.14%, p value = 0.98) in mouse and rat mammary glands, respectively. In conclusion, TaOx-nanoparticles are a suitable and versatile contrast agent for intraductal imaging and image-guided ablative procedures in rodent models of BC with translational potential to humans.

Systemic and Local Strategies for Primary Prevention of Breast Cancer

One in eight women will develop breast cancer in the US. For women with moderate (15-20%) to average (12.5%) risk of breast cancer, there are few options available for risk reduction. For high-risk (>20%) women, such as BRCA mutation carriers, primary prevention strategies are limited to evidence-based surgical removal of breasts and/or ovaries and anti-estrogen treatment. Despite their effectiveness in risk reduction, not many high-risk individuals opt for surgical or hormonal interventions due to severe side effects and potentially life-changing outcomes as key deterrents. Thus, better communication about the benefits of existing strategies and the development of new strategies with minimal side effects are needed to offer women adequate risk-reducing interventions. We extensively review and discuss innovative investigational strategies for primary prevention. Most of these investigational strategies are at the pre-clinical stage, but some are already being evaluated in clinical trials and others are expected to lead to first-in-human clinical trials within 5 years. Likely, these strategies would be initially tested in high-risk individuals but may be applicable to lower-risk women, if shown to decrease risk at a similar rate to existing strategies, but with minimal side effects.

Fourteenth Annual ENBDC Workshop: Methods in Mammary Gland Biology and Breast Cancer

The fourteenth annual workshop of the European Network for Breast Development and Cancer (ENBDC) on Methods in Mammary Gland Biology and Breast Cancer was held on April 26th - 29th in Weggis, Switzerland. For the first time, early career researchers organised and took part in an additional ECR workshop on the 26th of April, which was received with great enthusiasm. The topics of the main workshop included mammary branching and morphogenesis, novel experimental systems (model organisms), systemic influences on tumour progression and the tumour microenvironment. Novel and recent findings were shared across excellent oral and poster presentations.

Comparative mammary gland postnatal development and tumourigenesis in the sheep, cow, cat and rabbit: Exploring the menagerie

Sheep, cows, cats, and rabbits are kept by humans for agricultural purposes and as companion animals. Much of the mammary research in these species has focussed on mastitis in the case of ruminants and rabbits, and mammary tumourigenesis in cats and rabbits. However, similarities with the human breast suggest that these species may be currently underutilised as valuable comparative models of breast development and disease. The mammary gland undergoes cyclical postnatal development that will be considered here in the context of these non-traditional model species, with a focus on the mammary microenvironment at different postnatal developmental stages. The second part of this review will consider mammary tumour development. Ruminants are thought to be relatively 'resistant' to mammary tumourigenesis, likely due to multiple factors including functional properties of ruminant mammary stem/progenitor cells, diet, and/or the fact that production animals undergo a first parity soon after puberty. By contrast, unneutered female cats and rabbits have a propensity to develop mammary neoplasms, and subsets of these may constitute valuable comparative models of breast cancer.

Pathology of Diseases of Geriatric Exotic Mammals

The review covers select disease conditions most frequently described in aging rodents (rats, mice, hamsters, guinea pigs), rabbits, and ferrets. The conditions are categorized by general organ systems, infectious diseases, and neoplasms. Two data systems, the Veterinary Medical Teaching Hospital and Comparative Pathology Laboratory at the University of California, Davis and Zoo/Exotic Pathology Service, Citrus Heights, California were used in the determining disease conditions to describe.

Tumor Infiltrating Lymphocytes in Pet Rabbit Mammary Carcinomas: A Study with Relevance to Comparative Pathology

Simple Summary

The interaction between tumors and immune cells influences tumor fate, i.e., regression, growth, or even metastases. The evaluation of tumor infiltrating lymphocytes (TILs) in human breast cancer has prognostic value. Pet rabbits develop spontaneous mammary carcinomas and have an immune system that is comparable with that of humans, so that they have the potential to provide an animal model for human breast cancer. To further substantiate this similarity, this study examined TILs in 107 pet rabbit mammary carcinomas according to criteria established for human breast cancer. For TIL evaluation routinely stained microscopic sections were examined by light microscopy. Relevant histological and immunohistochemical tumor characteristics were obtained from a data base. Results showed that increased presence of stromal TILs was statistically associated with histological tumor features indicative of a less aggressive biological behavior, i.e., reduced tumor cell proliferation and a lower histological grade. The expression by tumor cells of calponin, a presumed tumor suppressor protein, was also associated with their reduced proliferation and a higher percentage of stromal TILs. Data suggest that higher percentages of stromal TILs may have the potential to serve as favorable prognostic indicator in rabbit mammary carcinomas and support the value of pet rabbits for comparative research.

Abstract

Tumor infiltrating lymphocytes (TILs) serve as prognostic biomarker in human breast cancer. Rabbits have the potential to act as animal model for human breast cancer, and close similarities exist between the rabbit and human immune system. The aim of this study is to characterize TILs in pet rabbit mammary carcinomas and to statistically correlate results with histological and immunohistochemical tumor characteristics. Microscopic evaluation of TILs was performed in hematoxylin and eosin stained sections of 107 rabbit mammary carcinomas according to international guidelines for human breast cancer. Data on histological features of malignancy, estrogen and progesterone receptor status and calponin expression were obtained from the data base. This study revealed a statistical association between stromal TILs in the central tumor (CT) and infiltrative margin. Higher maximal percentages of stromal TILs at the CT were statistically correlated with decreased mitotic count and lower tumor grade. An increased number of calponin positive tumor cells was statistically associated with a lower mitotic count and a higher percentage of stromal TILs. Results suggest that higher percentages of stromal TILs are useful biomarkers that may point toward a favorable prognosis in rabbit mammary carcinomas and support the concept of the use of rabbits for translational research.