Extracapsular extension and tumor implants in lymph nodes with canine mammary carcinoma metastasis: Study of the impact on survival

Small canine mammary tumours have different prognostic factors: A study of 3,470 tumours

Mammary gland neoplasms are the most frequent tumour in female dogs and most are malignant. Pet longevity and improvement in healthcare with early diagnosis increases the prevalence of cancer in animals. Tumour size is used as a prognostic factor to determine TNM (Tumour, Node, Metastasis) staging and considers tumours <3 cm, 3-5 cm and >5 cm. Due to the high rate of malignancy of mammary gland neoplasms, this study aimed to evaluate canine mammary tumours <3 cm and correlate the findings with clinicopathological parameters. A total of 3,470 mammary tumours were included and were classified as group 1 (G1, <1.5 cm) or group 2 (G2, 1.5-3 cm) as well as by prognosis - good, intermediate, poor or indeterminate. Clinicopathological parameters such as age, histological type, grade and lymph node status were analysed. The results revealed a significantly higher association of G1 tumours with non-neoplastic or benign diagnoses (P <0.001), a higher prevalence of histological grade I (P <0.001) and more frequent involvement of M2, M3 and M4 mammary glands (P <0.001). G2 tumours were significantly associated with a malignant diagnosis (P <0.001), higher prevalence of grades II and III (P <0.001), presence of lymph node metastasis (P <0.001) and involvement of the M5 mammary gland (P <0.001). Tumours with a good prognosis were most prevalent in dogs under 6 years old (mean 10 ± 2.8; P <0.0001) while a poor prognosis was significantly higher in dogs over 14 years old (mean 11.5 ± 2.8; P <0.0001). Tumours with an average size of 1.1 ± 0.7 cm had a significantly better prognosis (P <0.0001) and those with an average size of 1.6 ± 0.8 cm had a worse prognosis (P <0.0001). Histological type had an important role even in small tumours. Canine mammary tumours <1.5 cm and >1.5 cm had important differences in prognosis and highlight the need for a review of the minimal tumour size established in TNM staging for canine mammary gland tumours.

Canine, Feline, and Murine Mammary Tumors as a Model for Translational Research in Breast Cancer

In veterinary medicine, mammary tumors are the most common neoplasms in female dogs and the third most frequent in cats, representing a significant challenge. Efforts have been directed toward adopting standardized diagnostic criteria to better understand tumor behavior and progression in these species. Meanwhile, the use of animal models has substantially advanced the understanding of comparative mammary carcinogenesis. These models provide critical insights into factors responsible for the disease in humans, with the expectation that such factors can be identified and controlled. In this context, this review presents a work based mainly on articles published by a research group specializing in mammary pathology (Laboratory of Comparative Pathology-Department of General Pathology-ICB/UFMG) and its collaborators, complementing their results with literature findings. The publications were categorized into animal research, experimental research, and human research. These studies addressed topics such as diagnosis, prognostic and predictive factors, tumor microenvironment, inflammation associated with tumors, treatment approaches, and factors influencing tumor growth. The conceptual network analysis underscores the importance of in vivo breast cancer models, both experimental and spontaneous, for understanding tumor progression mechanisms and therapeutic responses, offering valuable contributions to veterinary and human oncology.

The role of lymph nodes and their drainage in canine mammary gland tumours: Systematic review

Mammary gland tumours are the most common neoplasms in intact bitches. Over the last decades, veterinary oncology has evolved in detecting and determining the lymph nodes to be removed in these patients for an accurate staging and prognosis, as well as to achieve better disease control and higher overall survival time. Our objective was to describe recent advances related to lymphatic drainage in bitches with mammary gland tumours, focusing on surgery, diagnosis, and prognosis. Through a systematic review using PubMed as the database, a thorough multi-step search reduced 316 studies to 30 for analysis. Vital dyes appear to be crucial in reducing the overall surgery time through transoperative staining of the lymph nodes. Imaging contrasts provide information regarding specific tumour drainage; however, there is still little evidence for their use. The axillary and superficial inguinal lymph nodes are well-established as regional lymph nodes of the cranial and caudal mammary glands. In sequence, accessory axillary, medial iliac, popliteal, and sternal lymph nodes should receive attention if they demonstrate contrast drainage, even considering that the literature has not shown a relationship between drainage and metastasis in these cases. In conclusion, recent studies have provided us with more support in regional lymph node excision regarding the TNM staging system. Studies are highly heterogeneous and method comparisons do not fit due to the non-uniformity of samples, materials, and procedures. We suggest further studies with a larger sample size, complete follow-up of patients, contrast use, and lymph node morphological and immunohistochemical analysis.

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.