Distribution, Risk Factors, and Histopathological Trends of Canine Testicular Tumors: What Clinicians Should Know

Testicular tumors in dogs are a common yet complex group of neoplasms with diverse histological origins and clinical implications. Their relatively high prevalence, estimated between 5% and 27%, is attributed to longer canine lifespans and the less frequent use of preventive castration^1,2. For clinicians, understanding the distribution patterns, risk factors, and histological variability of these tumors is essential for accurate diagnosis and management. 

Tumor Distribution and Histological Trends 

In non-multiple (solitary) testicular tumors, the most frequently diagnosed types are¹: 

• Seminomas (38.46%)  

• Interstitial (Leydig) cell tumors (37.12%)  

• Sertoli cell tumors (18.39%)  

These findings are broadly consistent with earlier studies, although some variation exists. For instance, Grieco et al. reported a predominance of interstitial cell tumors (~50%) and a lower proportion of Sertoli cell tumors (8%), while Švara et al. observed seminomas as the most common (47.8%)¹. Such discrepancies likely reflect differences in study design, population demographics, and sample sources. 

These tumors arise from distinct testicular components, explaining their varied histological appearances and clinical behaviors. Germ cell tumors may differentiate into seminomas or evolve into pluripotent forms such as embryonal carcinoma, teratoma, or yolk sac tumors, although the latter are less commonly reported in dogs. 

Role of Cryptorchidism and Developmental Disorders 

A significant and well-established risk factor is cryptorchidism, observed in 8.58% of cases in the current study, slightly higher than previous reports³. Undescended testes are particularly prone to developing Sertoli cell tumors, likely due to altered temperature regulation and hormonal environment. 

The risk of tumor development in cryptorchid testes is markedly elevated, with estimates suggesting a 14-fold increase¹. Similar associations are observed in humans, where conditions like androgen insensitivity syndrome and Klinefelter syndrome contribute to tumorigenesis¹. 

In dogs, disorders of sexual development have also been linked to tumor formation, reinforcing the role of genetic and developmental factors in oncogenesis¹. 

Bilateral Tumors and Clinical Implications 

Bilateral testicular tumors were identified in 7.97% of dogs, a figure comparable to previous studies¹. In some cases, each testis may harbor a different tumor type, adding another layer of diagnostic complexity. 

Importantly, the study found no statistically significant association between age, tumor location, or multiplicity, suggesting that these variables do not independently influence tumor development. This aligns with earlier findings and indicates that tumorigenesis is likely multifactorial. 

Hormonal Activity and Clinical Presentation¹ 

Beyond structural changes, certain tumors, particularly Sertoli cell tumors, may exhibit hormonal activity, leading to feminization syndromes, alopecia, or behavioral changes. Therefore, clinical evaluation should extend beyond palpation and imaging to include systemic signs that may indicate endocrine involvement. 

Diagnostic and Surgical Considerations¹ 

From a practical standpoint, the detection of testicular tumors often begins with physical examination and is followed by imaging and histopathological confirmation. However, clinicians must remain vigilant about the possibility of multiple or bilateral lesions, particularly in older or cryptorchid dogs. 

In human medicine, the presence of multiple lesions is considered an absolute contraindication for testis-sparing surgery, emphasizing the need for radical approaches in such cases. While veterinary protocols may differ, this highlights the importance of comprehensive preoperative assessment. 

Additionally, the study underscores the importance of histopathological consistency, noting that all evaluations were performed by a single pathologist, a limitation that future research should address through independent validation. 

Translational Value and Future Directions 

Dogs continue to serve as valuable models for human disease due to similarities in tumor biology and environmental exposure⁴. The increasing incidence of testicular tumors in both species underscores the need for continued research and collaboration between veterinary and human medicine. 

Clinical Relevance for Practice 

For clinicians, this study reinforces several key points. Testicular tumors are common and histologically diverse, requiring a systematic diagnostic approach. Cryptorchidism remains a major risk factor and should be addressed early. Bilateral and multiple tumors, although less common, must not be overlooked. 

Ultimately, a combination of clinical vigilance, imaging, and detailed histopathological analysis is essential for optimal patient outcomes. 

In summary, understanding the distribution and underlying risk factors of testicular tumors allows clinicians to move beyond basic diagnosis toward more informed, evidence-based management strategies, benefiting both veterinary patients and advancing comparative oncology research. 

References: 

1. Kuberka M, Prządka P, Dzimira S. Histological Analysis of Multiple Unilateral Testicular Tumors in Dogs. Life. 2025 Nov 19;15(11):1772. https://doi.org/10.3390/life15111772 

2. Ciaputa R, Gach J, Baranowski K, Dzimira S, Janus I, Kandefer-Gola M, Żebrowski K, Nowak M. Prevalence of tumours and tumour-like lesions in domestic and exotic animals from Lower Silesia and its surrounds in Poland in 2014–2017. Journal of veterinary research. 2022 Aug 30;66(3):427. https://sciendo.com/2/v2/download/article/10.2478/jvetres-2022-0036.pdf 

3. Manuali E, Forte C, Porcellato I, Brachelente C, Sforna M, Pavone S, Ranciati S, Morgante R, Crescio IM, Ru G, Mechelli L. A five-year cohort study on testicular tumors from a population-based canine cancer registry in central Italy (Umbria). Preventive veterinary medicine. 2020 Dec 1;185:105201. https://cris.unibo.it/bitstream/11585/819159/5/Manuscript_IP_EM160420.pdf 
4. Sultan F, Ganaie BA. Comparative oncology: Integrating human and veterinary medicine. Open veterinary journal. 2018 Jan 30;8(1):25. https://pmc.ncbi.nlm.nih.gov/articles/PMC5806664/pdf/OpenVetJ-8-25.pdf