The Link Between Cryptorchidism and Testicular Cancer in Dogs: Mechanisms, Evidence, and Clinical Interpretation

The association between cryptorchidism and testicular cancer in dogs is well recognized in veterinary medicine, yet its underlying mechanisms remain incompletely understood. While epidemiological studies consistently demonstrate an increased risk of neoplasia in retained testes, the causal relationship between these two conditions is still debated. Understanding this link is critical for veterinarians, as it directly influences clinical decision-making and long-term patient management. 

Epidemiological Evidence and Risk Magnitude 

Multiple studies have reported that cryptorchid dogs have a significantly higher risk of developing testicular tumors compared to dogs with normally descended testes. The relative risk has been estimated to range from 9.2 to 13.6 times higher in cryptorchid individuals. However, it is important to interpret these figures in context. Despite the increased relative risk, the absolute proportion of cryptorchid dogs that develop testicular tumors remains relatively low, with reported values of 3.1% and 5.7% in large cohort studies¹. 

This discrepancy highlights an important clinical nuance: while cryptorchidism is a strong risk factor, it is not sufficient on its own to cause tumor development. Additional factors, including genetic predisposition and environmental influences, likely contribute to tumorigenesis. 

Competing Theories Explaining the Association 

Two primary hypotheses have been proposed to explain the relationship between cryptorchidism and testicular cancer. The first is the temperature hypothesis, which suggests that the abnormal intra-abdominal or inguinal location of retained testes exposes them to higher temperatures. This altered thermal environment may disrupt normal germ cell maturation and promote neoplastic transformation¹. 

The second is the developmental or shared-origin hypothesis, which proposes that both cryptorchidism and testicular cancer arise from common genetic or environmental disturbances during fetal development. According to this theory, abnormalities in the development of the male reproductive system predispose individuals to both conditions simultaneously, rather than one directly causing the other ¹. 

These hypotheses are not mutually exclusive, and it is likely that both mechanisms contribute to the observed association. 

Cellular and Molecular Mechanisms 

At the cellular level, cryptorchidism is associated with significant alterations in germ cell and Sertoli cell populations. One of the most consistent findings is the persistence of gonocyte-like cells in cryptorchid testes. In dogs, these immature germ cells have been observed even in adult and senile animals, indicating a delay or arrest in normal differentiation². Additionally, cells positive for placental alkaline phosphatase (PLAP), a marker of gonocytes, have been detected in a substantial proportion of undescended testes³. 

This persistence of immature germ cells is particularly relevant to tumorigenesis. In humans, similar cells are considered precursors to germ cell neoplasia in situ, which can progress to seminomas and other germ cell tumors^1,4. Although the exact parallel in dogs remains unclear, these findings suggest a potential mechanistic link. 

Sertoli cells also undergo significant changes in cryptorchid testes. Increased expression of markers associated with immature Sertoli cells, such as AMH and inhibin alpha, has been reported^3,5. These alterations indicate a failure of normal maturation, which may contribute to the development of Sertoli cell tumors. Furthermore, disruption of the blood–testis barrier, characterized by abnormal expression of tight junction proteins such as claudins, has been observed in cryptorchid testes⁶. This disruption may lead to abnormal cell proliferation and tumor formation. 

Tumor Type Distribution in Cryptorchid Testes 

One of the most striking features of testicular tumors in cryptorchid dogs is the shift in tumor type distribution. Sertoli cell tumors are disproportionately represented in retained testes, accounting for up to 61.5% of tumors in some studies⁷. In contrast, their overall incidence in the general canine population is significantly lower. 

Seminomas are also more common in cryptorchid testes, although to a lesser extent. Interstitial cell tumors, on the other hand, are rarely observed in retained testes¹. This selective increase in specific tumor types suggests that the microenvironment of the cryptorchid testis plays a critical role in determining tumor development. 

Influence of Testicular Location 

The anatomical location of the retained testis may further influence tumor risk. Although limited data are available in dogs, studies have suggested that abdominal testes may be associated with earlier tumor development compared to inguinal or scrotal testes¹. This may be related to higher temperatures and more pronounced cellular alterations in the abdominal environment. 

In unilateral cryptorchidism, tumors are predominantly observed in the retained testis, while the contralateral scrotal testis appears to have a much lower risk. This supports the hypothesis that local environmental factors, rather than systemic influences, play a key role in tumorigenesis. 

Clinical Implications for Veterinary Practice 

From a clinical perspective, the association between cryptorchidism and testicular cancer underscores the importance of early intervention. Orchiectomy of retained testes is strongly recommended, not only to prevent genetic transmission but also to reduce the risk of neoplasia. 

Veterinarians should also be aware that tumors in cryptorchid dogs tend to occur at a younger age compared to those in dogs with normal testicular descent¹. This necessitates increased vigilance during routine examinations, particularly in middle-aged and older intact males. 

Conclusion 

The relationship between cryptorchidism and testicular cancer in dogs is complex and multifactorial. While epidemiological evidence clearly demonstrates an increased risk, the underlying mechanisms likely involve a combination of thermal, developmental, and cellular factors. For veterinarians, understanding these processes is essential for effective prevention, diagnosis, and management of testicular tumors in canine patients. 

Reference 

1. Soto-Heras S, Reinacher L, Wang B, Oh JE, Bunnell M, Park CJ, Hess RA, Ko CJ. Cryptorchidism and testicular cancer in the dog: unresolved questions and challenges in translating insights from human studies. Biology of reproduction. 2024 Aug;111(2):269-91. https://academic.oup.com/biolreprod/article-pdf/111/2/269/58824383/ioae075.pdf 

2. Hernandez-Jardon N, Rojas-Castaneda JC, Landero-Huerta D, Reyes-Cruz E, Reynoso-Robles R, Juarez-Mosqueda MDL, Medrano A, Reyes-Delgado F, Vigueras-Villasenor RM. Cryptorchidism: the dog as a study model. Front Vet Sci 2022; 9:935307. https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2022.935307/full 

3. Pecile A, Groppetti D, Pizzi G, Banco B, Bronzo V, Giudice C, Grieco V. Immunohistochemical insights into a hidden pathology: canine cryptorchidism. Theriogenology 2021; 176:43–53. https://air.unimi.it/bitstream/2434/887422/5/ManuscriptREV-draft.pdf 

4. Baroni T, Arato I, Mancuso F, Calafiore R, Luca G. On the origin of testicular germ cell tumors: from gonocytes to testicular cancer. Front Endocrinol (Lausanne) 2019; 10:343. https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2019.00343/pdf 
5. Jung HY, Yoo DY, Jo YK, Kim GA, Chung JY, Choi JH, Jang G, Hwang IK. Differential expression of estrogen receptor alpha and progesterone receptor in the normal and cryptorchid testis of a dog. Lab Anim Res 2016; 32:128–13. https://link.springer.com/content/pdf/10.5625/lar.2016.32.2.128.pdf