Most lesions found in the mammary glands of cats are malignant, with aggressive behavior and unfavorable prognosis. Studies on the epidemiologic and clinicopathological characteristics of mammary lesions in cats are scarce. The present study aimed to evaluate those characteristics and to correlate them with survival in cats. Mammary specimens were selected from 418 domestic cats that underwent surgical removal with or without lymphadenectomy. The cats and mammary lesions were evaluated for epidemiologic, clinical, and pathologic characteristics. Cats with malignant neoplasms were older than cats with benign neoplasms and non-neoplastic lesions; 858 lesions were identified, including sporotrichosis, basaloid carcinoma, and benign phyllodes, described for the first time in cats. Tubulopapillary and cribriform carcinomas were the most common malignant tumors found and were very similar in characteristics such as marked anisocytosis/anisokaryosis, high mitotic count (score 3) (p < 0.001), and presence of necrosis (p = 0.005). The association between advanced age and malignancy, as well as the description of new lesions, emphasizes the importance of population studies in cats to understand the behavior of the disease and to draw attention to diagnoses that should be considered in routine care.

Neospora caninum is an apicomplexan protozoan that is considered one of the main agents responsible for abortion in ruminants. The lesions found in the central nervous system (CNS) of aborted fetuses show multifocal necrosis, gliosis, and perivascular cuffs of mononuclear cells, but the inflammatory and glial cells have not been immunophenotypically characterized. The lesions in the CNS of infected adult animals have rarely been described. Therefore, in this study, we characterized the lesions, the immunophenotypes of the inflammatory and glial cells and the expression of MHC-II and PCNA in the CNS of goats infected with N. caninum. The CNS of eight aborted fetuses and six adult male goats naturally infected with N. caninum were analyzed with lectin histochemistry (RCA1) and immunohistochemistry (with anti-CD3, −CD79α, −GFAP, −MHC-II, and -PCNA antibodies). All animals were the offspring of dams naturally infected with N. caninum. The microscopic lesions in the CNS of the aborted fetuses consisted of perivascular cuffs composed mainly of macrophages (RCA1+), rare T lymphocytes (CD3+), and rare B lymphocytes (CD79α+). Multifocal necrosis surrounded by astrocytes (GFAP+), gliosis composed predominantly of monocytic-lineage cells (macrophages and microglia, RCA1+), and the cysts of N. caninum, related (or not) to the lesions were present. Similar lesions were found in four of the six male goats, and multinucleate giant cells related to focal gliosis were also found in three adult goats. Anti-GFAP immunostaining showed astrocytes characterizing areas of glial scarring. Cysts of N. caninum were found in three adult male goats. The presence of N. caninum was evaluated with histopathology, immunohistochemistry, and PCR. Immunohistochemistry demonstrated anti-PCNA labeling of macrophages and microglia in the perivascular cuffs and the expression of MHC-II by microglia and endothelial cells in the CNS of the aborted fetuses and adult male goats. Macrophages and microglia were the predominant inflammatory cells in the CNS of aborted fetuses and healthy adult male goats infected with N. caninum. Activated astrocytes were mainly associated with inflamed areas, suggesting that astrocytes were involved in the resolution of the lesions.

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 objective of this case report was to describe histopathological and immunohistochemical characteristics of the first reported basaloid carcinomas in the canine mammary gland. Two bitches were treated for tumors in the mammary gland and underwent mastectomy. Microscopic evaluation of these tumors revealed epithelial cells arranged in a predominantly solid pattern with hyperchromatic peripheral cells arranged in a palisade pattern. Metastases in regional lymph nodes were found in both animals, and one bitch exhibited pulmonary metastasis. Immunohistochemistry revealed positive labeling for the basal cell markers cytokeratin 14 and p63. Histopathological and immunohistochemical findings led to diagnoses of basaloid carcinoma of the canine mammary gland with regional and distant metastasis.

The malignant adenomyoepithelioma is a rare mammary tumor in women and uncommon in cats with only one report in this species. In this case report, the histopathological and immunohistochemical characteristics of six cases of malignant adenomyopithelioma in the feline mammary gland are described. Microscopic evaluation of tumors showed dense cellular neoplastic proliferation, composed of malignant myoepithelial and epithelial cells, formed by varied arrangements and presenting papillary, tubular and solid nest proliferation. Immunohistochemistry was performed for markers Ki67, Cox-2, RE, RP, p63 and HER-2. All cases were positive for p63, confirming the myoepithelial nature of neoplastic cells. The diagnosis of malignant adenomyopithelioma was made possible through the association between histopathological characteristics and immunohistochemical results.

In canine mammary neoplasms, greater inflammation is associated with higher histological grade, lymphatic invasion, and metastases. This retrospective study assessed the density of peri- and intratumoral tumor-infiltrating lymphocytes (TILs), tumor-associated neutrophils (TANs), and CD3⁺ and CD79⁺ lymphocytes in canine mammary neoplasms with a solid arrangement, and associated such data with histological types, immunophenotype, prognostic factors, cyclooxygenase-2 (Cox-2) expression and overall and cancer-specific survival. Sixty-one neoplasms with a solid arrangement were classified as malignant myoepitheliomas (6/9.8%), solid papillary carcinomas (8/13.1%), carcinomas with a solid pattern (9/14.8%), basaloid carcinomas (BC) (19/31.1%), and malignant adenomyoepitheliomas (19/31.1%). Intra- and peritumoral TILs, TANs, and TCD3⁺ and BCD79⁺ lymphocytes were counted, and based on the resulting median, the neoplasms were divided into low or high cell infiltration. BCs had the lowest density of intratumoral TILs (p = 0.02), and luminal B neoplasms showed a significantly higher density of intratumoral TCD3⁺ than luminal A cases. Neoplasms with a higher density of peritumoral CD3⁺ and CD79⁺ had significantly greater proliferative activity. High infiltration of intratumoral BCD79⁺ lymphocytes was related to nodal metastasis (p = 0.03). Intratumoral TILs and TCD3⁺ were associated with shorter survival time. Therefore, intratumoral lymphocyte infiltration is possibly an important feature in the progression of cancer and influences the survival in bitches with solid arrangement neoplasms.