Tracing the clinical profile of female dogs with mammary tumors: a decade of cases at the veterinary teaching Hospital of Universidade Federal FluminenseABSTRACT
Mammary cancer is the most common neoplasm in female dogs, characterized by high variability in biological behavior. This observational and retrospective study analyzed the clinical profile of 404 female dogs diagnosed with mammary cancer between 2013 and 2023 at the Veterinary Teaching Hospital Professor Firmino Marsico Filho of Federal Fluminense University (HUVET - UFF), in Niterói, RJ, Brazil. The average age was 9.8 years, with a predominance of mixed-breed (34.16%) and non-spayed females (70.05%), highlighting the impact of reproductive status on neoplasia prevalence. Carcinoma in mixed tumor was the most common histological type (n=220), and clinical stage I was the most frequent (44.80%). There was a high rate of non-adherence to chemotherapy (78.8%), despite the predominance of early-stage diagnoses (55.68%). Early diagnosis, educational policies focused on reproductive health in female dogs, and access to specialized treatment are crucial for better prognosis and quality of life in these animals.
Keywords:
mammary cancer; female dogs; lymphadenectomy; veterinary oncology
RESUMO
O câncer de mama é a neoplasia mais comum em cadelas, caracterizada por uma alta variabilidade de comportamento biológico. Este estudo observacional e retrospectivo analisou o perfil clínico de 404 cadelas diagnosticadas com câncer de mama entre 2013 e 2023 no Hospital Universitário de Medicina Veterinária Professor Firmino Marsico Filho da Universidade Federal Fluminense (HUVET - UFF), em Niterói, RJ. A idade média foi de 9,8 anos, com predomínio de cadelas sem raça definida (34,16%) e inteiras (70,05%), reforçando o impacto do status reprodutivo na prevalência da neoplasia. O carcinoma em tumor misto foi o tipo histológico mais comum (n=220), e o estágio clínico I o mais frequente (44,80%). Houve uma alta taxa de não adesão ao tratamento quimioterápico (78,8%), apesar da predominância de estágios iniciais (55,68%). O diagnóstico precoce, as políticas educacionais voltadas à saúde reprodutiva de cadelas e o acesso a tratamento especializado são cruciais para o melhor prognóstico e qualidade de vida desses animais.
Palavras-chave:
câncer de mama; cadelas; linfadenectomia; oncologia veterinária
INTRODUCTION
Canine mammary tumors are the most diagnosed tumors in female dogs, representing a significant challenge in veterinary medicine due to its high incidence and clinical complexity. Brazilian studies indicate that these neoplasms account for more than half of tumor diagnoses in female dogs, with malignancy rates exceeding 80% in certain populations (Cassali et al., 2014; Nunes et al., 2018).
Epidemiological factors such as age, reproductive status, and the use of contraceptives have been associated with the development of mammary tumors in female dogs (Sorenmo et al., 2013; Santos et al., 2020). Increased susceptibility is observed in intact females, especially in older ages (Sorenmo et al., 2013). Additionally, clinical aspects, such as tumor size, histological grade, and involvement of regional lymph nodes, play a crucial role in disease progression and patient prognosis (Cassali et al., 2014).
This study aims to characterize the clinical and epidemiological aspects of mammary neoplasms in female dogs treated in the city of Niterói, Metropolitan Region of Rio de Janeiro, over a decade. Factors such as age, reproductive status, clinical staging, histopathological characteristics, and therapeutic outcomes were analyzed. Understanding these factors is essential to guide preventive strategies, improve clinical management, and optimize therapeutic outcomes in female dogs affected by mammary tumors.
ETHICAL ASPECTS
The research was submitted to the Ethics Committee on Animal Use of Universidade Federal Fluminense, and approved under the number CEUA 6529270623 (ID001854).
MATERIALS AND METHODS
This study was conducted using data from the Veterinary Teaching Hospital Professor Firmino Marsico Filho of the Federal Fluminense University (HUVET - UFF) in Niterói, located in the metropolitan region of Rio de Janeiro.
This was a retrospective cohort study, with information collected from medical records of canine patients treated at the hospital between 2013 and 2023. The study population included female dogs that underwent mastectomy and lymphadenectomy procedures with a histopathological diagnosis of malignant mammary tumors. Animals operated at external hospitals were excluded.
The surgical technique was based on the number and location of lesions, considering lymphatic drainage, tumor size, and the presence of adhesions. Regional or unilateral radical mastectomy was selected accordingly. In cases of multiple tumors, the procedure was initiated on the chain containing the largest tumor. Before surgery, patients underwent comprehensive clinical staging, including physical examination; tumor and regional lymph node assessment and measurement; cytological evaluation of nodules; hematological and biochemical testing; thoracic radiography; and abdominal ultrasonography.
Data were collected from the records of the Surgical Clinic, Veterinary Oncology, and Anesthesiology departments. A total of 404 patients were identified between 2013 and 2023, from which only female dogs undergoing total or regional mastectomy, with or without concomitant ovariohysterectomy, were selected. The information was organized into spreadsheets containing data such as age, reproductive status, contraceptive use, date of diagnosis, histological type and grade, lymph node status, treatments, recurrence, metastasis, and chemotherapy.
Clinical staging followed the TNM system adapted for mammary tumors in female dogs, assessing tumor size (T1, 0-3cm; T2, 3-5cm; T3, >5cm), involvement of regional lymph nodes (N0, non-metastatic; N1, metastatic), and the presence of distant metastasis (M0, non-metastatic; M1, metastatic). Patients were divided into stages I to V, as follows: I (T1N0M0); II (T2N0M0); III (T3N0M0); IV (T1,2,3N1M0); and V (T1,2,3N0,1M1) (Owen, 1980; Rutteman et al., 2001). Tumors were fixed in 10% formalin, analyzed via histopathology, and classified according to the Brazilian Consensus for Diagnosis, Prognosis, and Treatment of Canine Mammary Neoplasms (Cassali et al., 2014, 2020). Histopathological grading criteria followed the systems of Elston and Ellis (1998) and Goldschmidt et al (2011).
Analysis of epidemiological variables, such as age, size, breed, reproductive status, contraceptive use, and uterine changes, was conducted. Local recurrences, new tumors, and distant metastases were diagnosed through physical examinations, biopsies, and imaging studies. Chemotherapy protocols followed the recommendations of the Brazilian Consensus for Mammary Neoplasms (Cassali et al., 2014, 2020), considering the individual characteristics of patients and the financial resources of owners.
Data analysis was performed using R software (version 4.4.2), with descriptive statistics and hypothesis testing employed to evaluate associations between clinical and epidemiological variables.
RESULTS
The age of the female dogs ranged from 3 to 17 years, with an average age of 9.8 years. Multiple mammary nodules were present in 78.0% of cases, with 92.0% of tumors localized to the caudal abdominal and inguinal mammary glands.
Reproductive data revealed that 70.1% (n=283) were intact females undergoing concurrent ovariohysterectomy and mastectomy. The administration of contraceptive hormones was reported by only 2.72% of the owners, and no direct correlation with tumor malignancy was found.
Small-breed dogs predominated (37.6%), with mixed breeds representing the largest subgroup (34.2%). The most frequent pure breeds were Poodle (22.3%), Yorkshire Terrier (8.9%), and Dachshund (7.9%).
Regarding clinical staging, most cases were in stage I (44.80%), while 25.0% were in stage III. Early stages (I to III) were the most common (84.90% of cases), whereas stage IV patients represented 15.10% (n=61), and 65.84% of early-stage patients did not undergo lymphadenectomy.
Unilateral total mastectomy was the most performed procedure (98.02% of cases). Grade III tumors were frequently associated with more advanced clinical stages (III and IV), with lymphatic involvement identified in 36.67% of these cases. The most observed histological types were Carcinoma in Mixed Tumor (n=220), followed by Mammary Carcinosarcoma (n=44), Papillary Mammary Carcinoma (n=27), and Solid Mammary Carcinoma (n=27).
Adjuvant chemotherapy (mean cycles: 4±1.92) was administered to 21.8% of cases, with 55.7% of treated dogs in early stages (I-II). Long-term follow-up (>12 months) correlated significantly with stage I disease and absence of lymphatic metastasis.
DISCUSSION
The age distribution of female dogs in this study (3-17 years, average 9.8 years) aligns with established literature identifying older, intact females as the highest risk population for mammary tumors (Sorenmo et al., 2013). The predominance of intact females (70.05%) reinforces the protective effect of early ovariohysterectomy, where prolonged exposure to ovarian hormones elevates mammary tumor risk (Schneider et al., 1969). While early sterilization significantly reduces mammary cancer risk, some authors report associated increases in other neoplasms, urinary incontinence, and orthopedic disorders, particularly when performed before skeletal maturity (Torres de La Riva et al., 2013; Hart et al., 2020a, 2020b). These findings have led to new recommendations for timing sterilization between the first and second estrous cycles as a balance between oncological prevention and overall health preservation (Cassali et al., 2020).
The caudal/inguinal predominance (92.0%) of tumors reflects both the higher glandular density in these regions and their prolonged hormonal exposure during estrous cycles (Misdorp, 2002). Our finding of 78.0% multiple nodules supports the standard practice of unilateral mastectomy (performed in 98.0% of cases) when disease is confined to one mammary chain (Cassali et al., 2020).
While contraceptive hormone use was rare (2.7%) in our cohort, its known association with myoepithelial hyperplasia and subsequent malignant transformation (Misdorp, 2002; Torres, 2021) warrants continued caution in clinical practice.
The predominance of mixed-breed and small-sized dogs may reflect regional demographic trends of the metropolitan region of Rio de Janeiro, where smaller breeds are often preferred as companion animals. While studies report increased mammary tumor risk in purebred and small-sized dogs (Edmunds et al., 2023), others demonstrate significant geographic variation in breed-specific predisposition (Vascellari et al., 2016; Nunes et al., 2018; Pastor et al., 2018). These apparent discrepancies may be explained by regional differences in breed populations, highlighting the importance of considering local demographics when interpreting epidemiological data.
Regarding clinical staging, most cases were stage I (44.80%), followed by stage III (25.0%), suggesting that many tumors were detected before significant progression-a critical factor for improving prognosis. Early-stage disease (stages I to III) accounted for most cases (84.90%), consistent with findings by Nunes et al. (2018). Stage IV cases represented 15.10% (n=61), though the 65.8% rate of omitted lymphadenectomy in these cases raises concerns about potential understaging. Given the prognostic significance of nodal status (Cassali et al., 2020), future studies should evaluate the impact of routine lymphadenectomy on staging accuracy and survival outcomes.
The predominance of Carcinoma in Mixed Tumor as the most common histological type further corroborates findings from other studies, emphasizing its clinical relevance in canine mammary cancer (Cassali et al., 2009; Toríbio et al., 2012). Grade III tumors were frequently associated with more advanced clinical stages (III and IV), with lymphatic involvement identified in 36.67% of these cases, similar to findings from other studies showing greater lymphatic involvement in high-grade carcinomas (Karayannopoulou, 2005; Nunes et al., 2018).
The low chemotherapy adherence rate (78.2% untreated) likely reflects both financial constraints and limited access to specialized care, which may hinder optimal treatment outcomes. Of the patients undergoing adjuvant chemotherapy, 55.68% were in early stages (I and II), suggesting that the therapy may have contributed to greater survival in these cases. However, it is important to consider that the less aggressive nature of these tumors may have positively influenced outcomes regardless of therapeutic intervention. Future studies should investigate the isolated contribution of chemotherapy to survival in patients at different clinical stages.
Patients who maintained regular follow-up for more than 12 months predominantly exhibited early-stage disease (Stage I; 44.8%) without lymphatic involvement. These data highlight the critical importance of both early intervention and owner compliance in achieving optimal outcomes.
CONCLUSION
This retrospective study reinforces that mammary tumors in female dogs are highly prevalent in the routine of the Veterinary Teaching Hospital Professor Firmino Marsico Filho at the Fluminense Federal University (HUVET - UFF), particularly in small-sized, older, and intact animals. The high frequency of non-spayed dogs, combined with low adherence to chemotherapy, highlights the importance of public policies focused on reproductive health education and improving access to specialized treatments.
Early-stage tumors, such as stage I, and mixed tumors were the most frequently observed, indicating that early detection and appropriate clinical interventions are critical factors for improving the prognosis and quality of life of affected patients.
The analysis further emphasizes the need for additional studies to understand the isolated impact of adjuvant therapies, as well as the challenges posed by the biological heterogeneity of mammary tumors in female dogs. Larger sample sizes and long-term follow-up studies may support the development of more effective and personalized therapeutic approaches, enhance prognostic tools, and help identify improved adjuvant therapies.
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