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Tumors of the Male Reproductive System

Trina Hazzah, DVM, DACVIM (Oncology)

VCA West Los Angeles Animal Hospital, Los Angeles, CA, USA

Testicular Tumors Signalment

Testicular tumors are diagnosed in older dogs, with a
Etiology/Pathophysiology median age of approximately 10 years. No specific breed
Testicular tumors are the most common cancer found in predilection has been consistently described.
the male reproductive tract and are typically considered
nonaggressive. Primary testicular neoplasia commonly History and Clinical Signs
arises from three separate areas of the testis: the susten­
tacular cells of Sertoli (Sertoli cell tumors), interstitial Sertoli cell tumors are often large (1–5 cm). Atrophy of
cells (Leydig cell tumors), and germinal epithelium (sem­ the contralateral testicle is common. Dogs with Sertoli
inoma). A recent study evaluated 345 testicular tumors; cell tumors can present with bilateral dorsal alopecia,
seminomas (33.9%) were the most common followed hyperpigmentation of the skin or scrotum, enlarged nip­
by interstitial cell tumors (33%), and lastly Sertoli cell ples, squamous metaplasia of the prostate, gynecomas­
tumors (26.4%). Although less frequently seen, other tumor tia, and thinning of the skin. Many of these clinical signs
types can be found such as lymphoma, hemangiosarcoma, are associated with hyperestrogenism which causes signs
and others. of feminization and is found in approximately 20% of
cases. Severe bone marrow hypoplasia leading to life‐
threatening pancytopenia can result from the excessive
Epidemiology
endogenous estrogen production from the tumor.
The prevalence of testicular tumors in dogs is 27%, which Leydig cell tumors are relatively small (usually under
has increased from previous years. A cryptorchid testicle 2 cm) in size, and can be found as either solitary or mul­
has an approximately 10 times increased risk of develop­ tiple and unilateral or bilateral.
ing cancer compared to a descended testicle. This effect Seminomas are larger tumors (can be greater than
may be in part due to the higher temperature of the 5 cm) and often appear as nodules. They can occur along
retained testis within the body. Of retained testes tumors, with interstitial and Sertoli cell tumors. Hyperestrogenism
34% are seminomas and 54% are Sertoli cell tumors. is rarely seen with this tumor type although a recent case
Other risk factors are age, breed, and exposure to envi­ study described a 5‐year‐old Yorkshire terrier with con­
ronmental carcinogens. In one study, intact dogs over 6 firmed hyperestrogenemia and secondary alopecia.
years of age had an increased incidence of testicular
tumors. Collies and Shetland sheepdogs were five times
more likely to develop testicular tumors, specifically Diagnosis
Sertoli cell tumors. Environmental carcinogen exposure Staging with full blood analysis, urinalysis, thoracic radi­
has also been a proven risk factor. ographs, and abdominal ultrasound should be performed
Military working dogs in the Far East that were exposed in all patients with testicular tumors. Results typically
to chemical sprays like Agent Orange, herbicides, and reveal no abnormalities unless the presence of hyperes­
dioxin demonstrated an increased risk of seminomas. trogenemia results in blood dyscrasias or pancytopenia.

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical