Feline mammary tumors (FMTs) are among the most frequently diagnosed neoplasms in cats, representing nearly on third of all feline tumors (Cassali et al., 2025). They rank after hematopoietic and skin tumors in prevalence and are considered the most common neoplastic condition in intact female cats. Unlike canine mammary tumors, which display a broad histological heterogeneity, feline mammary tumors are less diverse but far more aggressive, with malignant carcinomas accounting for more than 80% of cases (Zhelavskyi et al., 2023; Nakagaki et al., 2021). Similar epidemiological patterns have been reported in different countries, where retrospective studies confirm their high frequency and poor prognosis (Ariyarathna et al., 2022; Aupperle-Lellbach et al., 2022).
       
The epidemiology of FMTs reflects several risk factors. Age is an important determinant, with the majority of cases diagnosed in cats between 9 and 11 years (Simeonov et al., 2023). Tumors are rare in animals under five years old and their incidence increases significantly thereafter. Hormonal influence is well established: Prolonged exposure to estrogens and progestagens strongly predisposes to mammary carcinogenesis (Laïssaoui et al., 2024). Preventive spaying markedly reduces the risk-cats ovariectomized before six months of age have only a 9% risk of developing mammary carcinoma compared with intact females, while those spayed after one year show little to no reduction (Pickard et al., 2023; Ferreira et al., 2024). Large-scale epidemiological studies reinforce the protective role of early spaying and highlight geographic differences in prevalence (Price et al., 2023).
       
Breed predisposition remains controversial. Some studies suggest that Siamese and domestic shorthair cats are more likely to develop mammary tumors, with Siamese cats often affected at a younger age than other breeds (Simeonov et al., 2023). Genetic, hormonal and environmental factors likely interact to influence susceptibility. Experimental and clinical studies in both cats and dogs underline the relevance of breed and geographic distribution in mammary tumor development (Cassali et al., 2020; Ariyarathna et al., 2022).
       
Histologically, feline mammary tumors are classified mainly as carcinomas of epithelial origin, including tubulopapillary, cribriform, solid and micropapillary variants (Zappulli et al., 2019; Zhelavskyi et al., 2023). Less common histotypes include lipid-rich carcinoma, mucinous carcinoma and squamous cell carcinoma. Benign tumors, though uncommon, consist of adenomas, fibroadenomas and mixed tumors, while fibroepithelial hyperplasia is frequently associated with exogenous progestagen administration (Queiroga et al., 2021; Torrigiani et al., 2022). Additional reports emphasize unusual histological subtypes such as adenomyoepitheliomas and rare variants of epithelial-myoepithelial tumors (Ali et al., 2021; Nunes et al., 2021). Recent consensus guidelines have also refined diagnostic, prognostic and therapeutic criteria, highlighting the importance of histological pattern and molecular markers (Cassali et al., 2020; Cassali et al., 2024).
       
From a clinical perspective, feline mammary tumors are highly invasive and metastatic, with frequent spread to regional lymph nodes and lungs. Prognosis is generally poor and radical mastectomy is the treatment of choice (Petrucci, 2020). Prognostic markers such as necrosis quantification and staging systems have recently been proposed to improve clinical decision-making (Rodrigues-Jésus et al., 2024; Monteiro et al., 2025). Comparative oncology has also highlighted the importance of feline mammary carcinoma as a natural model of human breast cancer, given its spontaneous occurrence, aggressive nature and biological similarities (Cassali et al., 2025).
       
Despite the growing literature, regional epidemiological and histopathological data on feline mammary tumors remain limited in North Africa. Algeria, where pet ownership and veterinary care are expanding, still lacks comprehensive reports on feline mammary pathology.
               
The aim of the present study was therefore to describe the prevalence, histopathological features and distribution of mammary tumors in cats from Northeastern Algeria and to compare these findings with previous international reports.

Between November 2022 and November 2024, sixty female cats (Siamese and crossbred), aged 8-10 years, were examined at the Veterinary Clinic of the Institute of Veterinary Sciences, University of Constantine. The animals originated from Skikda and Sétif provinces in Northeastern Algeria and none had undergone ovariectomy or hormonal treatment with progestagens.
       
All sixty cats were evaluated regardless of the presence of mammary abnormalities. Among them, only the thirty animals showing clinical mammary lesions were selected for surgical sampling and subsequent histopathological examination. Thus, the histopathological findings reported in this study pertain exclusively to these thirty lesion-positive cases.

Clinical examination
 
Preliminary evaluation was performed in collaboration with private veterinarians. During clinical examination, mammary masses were palpated and localized, most commonly in the caudal abdominal and inguinal glands due to their larger mammary tissue volume.
 
Surgical sampling
 
Thirty cats (50%) presented mammary lesions and underwent radical mastectomy. Excised specimens were forwarded to the Pathology Laboratory of the University Hospital of Constantine with accompanying clinical information.
 
Histological processing
 
Tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned at 4 µm and stained with hematoxylin and eosin (H and E). Microscopic evaluation was carried out using the classifications of Zappulli et al., (2019) and Zhelavskyi et al., (2023).

Out of the 60 cats examined, 30 (50%) presented mammary lesions confirmed by histopathology. Among these, 18 cases (30%) were malignant tumors, 9 (15%) were benign tumors and 3 (5%) were atypical hyperplasias. No significant differences in prevalence were found between Siamese and crossbred cats (P=1). The mean age of affected Siamese cats was 9±0.816 years, while crossbred cats showed a similar mean age of 9±0.187 years (Table 1). Most affected animals were between 8 and 10 years old.


       
Macroscopically, mammary tumors appeared as firm nodules, often ulcerated and infiltrating the caudal abdominal and inguinal glands, which represent the largest mammary complexes (Fig 1-3). Tumor masses varied in size and consistency, with some presenting as mobile, inflamed lesions and others as firm, irregular or polypoid nodules with hemorrhagic and necrotic areas.






       
Microscopically, malignant epithelial carcinomas were predominant and displayed a wide histological diversity. The most frequent subtypes were complex carcinoma and tubulopapillary carcinoma (Fig 4-5). Invasive micropapillary, cribriform, comedocarcinoma and squamous cell carcinoma were also detected (Fig 9-13). Less common variants, such as lipid-rich carcinoma, adenosquamous carcinoma and papillary cystic carcinoma, were recorded in isolated cases (Fig 6-8, 14). Carcinomas with malignant myoepithelioma were observed, highlighting the heterogeneous histogenesis of feline mammary tumors (Fig 7).






















       
Benign tumors accounted for 15% of cases and included mixed tumors with osseous and cartilaginous metaplasia (Fig 15-17). Basaloid adenoma and basaloid ductal adenoma were also identified among the benign tumors. These lesions showed typical basaloid proliferation patterns without evidence of malignant transformation. Other benign lesions consisted of complex adenomas and canalicular adenomas (Fig 18-19). The identification of osseous and cartilaginous differentiation was particularly notable given its rarity in feline species.










       
Hyperplastic lesions were less frequent and consisted exclusively of atypical ductal hyperplasia (Fig 20), considered a potential precursor to carcinoma.


       
Overall, malignant tumors represented the majority of mammary lesions, followed by benign tumors and a smaller proportion of atypical hyperplasia (Table 2). The histological findings emphasize both the aggressiveness and heterogeneity of feline mammary tumors in the studied population.


       
This study confirms the high prevalence and aggressiveness of feline mammary tumors (FMTs) in Northeastern Algeria. Half of the examined cats presented mammary lesions, with malignant carcinomas representing 60% of cases. These results are consistent with international findings, which report that 80-90% of feline mammary tumors are malignant (Zhelavskyi et al., 2023; Nakagaki et al., 2021). Similar trends of high malignancy have also been described in canine mammary tumors, where aggressive biological behavior is frequently linked to molecular alterations such as p53 overexpression (Veena et al., 2025), supporting the concept that mammary neoplasms across species share comparable oncogenic pathways.
       
The mean age of affected cats (9 years) corresponds to that described in the literature, with most cases occurring in middle-aged to older intact females (Simeonov et al., 2023; Pickard et al., 2023). Although Siamese cats have been reported to be at higher risk (Laïssaoui et al., 2024), our findings did not show significant breed influence. This may reflect the limited sample size or suggest that hormonal exposure and age are more important determinants than breed. Similar observations have been recorded in canine studies, where Dachshunds and other breeds develop mammary tumors primarily due to hormonal and reproductive factors rather than breed predisposition alone (Sarkar et al., 2022).
       
Histologically, carcinomas showed remarkable heterogeneity, with tubulopapillary, cribriform, micropapillary and squamous cell carcinomas predominating. Complex carcinomas and comedocarcinomas were also observed. Less common variants such as lipid-rich and papillary cystic carcinoma, although rare, were identified, confirming the wide morphological spectrum of FMTs (Geovanni et al., 2025). Benign lesions such as complex adenomas and canalicular adenomas were rare, as expected in feline species (Queiroga et al., 2021). The presence of stromal remodeling in some tumors may resemble findings in other species, where proteolytic enzymes like MMP-11 (stromelysin-3) have been shown to contribute to invasive behavior (Sahoo et al., 2015), further reinforcing the aggressive histological nature of mammary carcinomas.
       
The detection of mixed tumors with osseous and cartilaginous metaplasia in this study is noteworthy. Although uncommon in cats, such tumors have been recently described (Monteiro et al., 2025). Their occurrence suggests the capacity of feline mammary epithelial and myoepithelial cells to undergo metaplastic transformation, resembling some canine and human breast lesions. Such plasticity has also been observed in canine tumors undergoing multiphenotypic differentiation during progression (Sarkar et al., 2022).
       
The observation of atypical ductal hyperplasia highlights the continuum between non-neoplastic proliferative lesions and carcinoma. Such lesions are considered preneoplastic and carry a significant risk of malignant transformation (Pickard et al., 2023; Souza et al., 2024). Their identification underlines the importance of systematic histological examination, even in small nodules, to establish an accurate prognosis. Molecular studies in rodent mammary tumor models have shown that early proliferative changes often coincide with altered gene expression stability (Arora et al., 2021), suggesting potential for future molecular characterization in feline lesions as well.
       
From a comparative oncology perspective, feline mammary carcinoma shares several biological features with human breast cancer, including its spontaneous development, hormonal influence, histological diversity and aggressive clinical behavior. This supports the use of the cat as a relevant model for translational breast cancer research (Geovanni et al., 2025). Furthermore, therapeutic advances in other species-such as low-dose metronomic chemotherapy shown to be beneficial in canine mammary tumors (Sowbharenya et al., 2018) -may provide alternative avenues for future investigation in feline oncology.
       
In Algeria, the increasing popularity of companion animals and the establishment of specialized veterinary services provide opportunities to improve early detection and treatment. However, awareness among owners and veterinarians remains essential, as delayed presentation and diagnosis may compromise outcomes. Radical mastectomy remains the recommended treatment, as conservative excision is usually followed by recurrence. Preventive ovariectomy before the first estrus remains the most effective strategy for reducing the risk of mammary tumors (Ferreira et al., 2024).

Feline mammary tumors in Northeastern Algeria were highly prevalent and predominantly malignant. The majority were invasive carcinomas with aggressive histological patterns, while benign tumors and atypical hyperplasias were less common. These findings emphasize the need for early diagnosis and systematic histopathological evaluation to guide treatment and prognosis. Radical mastectomy should be considered the standard therapeutic approach and preventive spaying before the first estrus remains the most efficient method to reduce the risk of mammary tumors in cats. Beyond clinical relevance, the biological similarities between feline mammary carcinoma and human breast cancer reinforce its role as a valuable comparative model in oncology.

No external funding was received for this study.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
All animal procedures for experiments were approved by the Committee of Experimental Animal care and handling techniques were approved by the University of Animal Care Committee.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.