High Intrinsic Expression of P-glycoprotein and Breast Cancer Resistance Protein in Canine Mammary Carcinomas Regardless of Immunophenotype and Outcome

Mammary Glands of Women, Female Dogs and Female Rats: Similarities and Differences to Be Considered in Breast Cancer Research

Breast cancer is one of the most common and well-known types of cancer among women worldwide and is the most frequent neoplasm in intact female dogs. Female dogs are considered attractive models or studying spontaneous breast cancer, whereas female rats are currently the most widely used animal models for breast cancer research in the laboratory context. Both female dogs and female rats have contributed to the advancement of scientific knowledge in this field, and, in a "One Health" approach, they have allowed broad understanding of specific biopathological pathways, influence of environmental factors and screening/discovery of candidate therapies. This review aims to clearly showcase the similarities and differences among woman, female dog and female rat concerning to anatomical, physiological and histological features of the mammary gland and breast/mammary cancer epidemiology, in order to better portray breast tumorigenesis, and to ensure appropriate conclusions and extrapolation of results among species. We also discuss the major aspects that stand out in these species. The mammary glands of female dogs and women share structural similarities, especially with respect to the lactiferous ducts and lymphatic drainage. In contrast, female rats have only one lactiferous duct per nipple. A comprehensive comparison between humans and dogs is given a special focus, as these species share several aspects in terms of breast/mammary cancer epidemiology, such as age of onset, hormonal etiology, risk factors, and the clinical course of the disease. Holistically, it is clear that each species has advantages and limitations that researchers must consider during the development of experimental designs and data analysis.

HER2 Overexpression and Cytogenetical Patterns in Canine Mammary Carcinomas

Human epidermal growth factor receptor 2 (HER2) is a tyrosine kinase receptor that promotes tumor cell growth and is implicated in the pathogenesis of human breast cancer. The role of HER2 in canine mammary carcinomas (CMCs) is not clear. Therefore, this study aimed to examine the protein expression and cytogenetic changes of HER2 and their correlation with other clinical–pathological parameters in CMC. We retrospectively selected 112 CMCs. HER2, ER, and Ki67 were assessed by immunohistochemistry. HER2 antibody validation was investigated by immunoblot on mammary tumor cell lines. Fluorescence in situ hybridization (FISH) was performed with probes for HER2 and CRYBA1 (control gene present on CFA9). HER2 protein overexpression was detected in 15 carcinomas (13.5%). A total of 90 carcinomas were considered technically adequate by FISH, and 8 out of 90 CMC (10%) were HER2 amplified, 3 of which showed a cluster-type pattern. HER2 overexpression was correlated with an increased number of HER2 gene copies (p = 0.01; R = 0.24) and overall survival (p = 0.03), but no correlation with ER, Ki67, grade, metastases, and tumor-specific survival was found. Surprisingly, co-amplification or polysomy was identified in three tumors, characterized by an increased copy number of both HER2 and CRYBA1. A morphological translocation-fusion pattern was recognized in 20 carcinomas (22%), with a co-localized signal of HER2 and CRYBA1. HER2 is not associated with clinical–pathological parameters of increased malignancy in canine mammary tumors, but it is suitable for studying different amplification patterns.

The development of molecular typing in canine mammary carcinomas

Mammary tumors are the most frequent neoplasia in old female dogs and present challenges in diagnosis and prognosis owing to heterogeneity. Along with the rapid development of biotechnology, the molecular subtyping of canine mammary carcinomas has been researched, and provides an important reference basis for diagnosis, treatment, prognosis, and even prediction of recurrence rate. Therefore, the molecular classification of canine mammary carcinomas has gained a broad clinical application prospect. However, the existing molecular markers of canine mammary carcinomas are still unable to meet the expanding clinical needs with poor clinical feasibility. Thus, it is urgent to develop more applicable biomarkers appropriate for personalized treatment modalities. At present, the molecular typing of canine mammary carcinomas is not fully understood, and it is first reviewed in this study.

Prognostic markers of canine mammary tumours: Retrospective study of 142 cases

Due to relevance of the problem, prediction of biological behaviour of neoplasias in mammary glands of dogs requires using contemporary approaches to the study, first of all, of ways of dissemination of tumour cells. One of them is studying the mechanisms of migration of cancer cells out of the neoplasm tissues with further dissemination and development of metastatic sites in the regional lymphatic nodes and remote tissues. We studied the survival period of bitches with tumours of the mammary glands following regional or unilateral mastectomy. Among malignant mammary tumours in bitches, the most often diagnosed were single tumours (57.5%), which histologically were classified to carcinomas – ductal (26.9%) and mixed type (21.9%). Probability of intratumoral invasion to blood vessels equaled 12.0%, to lymph vessels – 7.8%, lymph nodes – 12.8%. It depends on the histological type of the tumour, the most aggressive potentially being сomedocarcinoma, tubulopapillary carcinoma and ductal carcinoma. Parameters of life expectancy and survival level after mastectomy depend on clinical stage of the disease (increase in the stage from the first to the third was characterized by decrease from 12.8 ± 9.5 to 9.4 ± 7.8 months), presence of angio/lymphatic invasions, presence of angiolymphatic invasion, but had no correlation with the size of the tumours. An important predictor of tumour-related death of dogs suffering neoplasias of the mammary glands is index vet-NPI, which has significant correlation with the clinical stage according to Owen and median survival. In particular, median survival in patients with the index lower than 4 exceeded the corresponding values in dogs with the index above 4 by 1.3 times. A promising direction of further research would be studying biological mechanisms of development of tumour emboli in the blood and lymph vessels, metastatic sites in lymph nodes, and also determining their role in pathogenesis of canine mammary tumours.