Testicular tumors are common in male dogs. In fact, it's estimated 4% to 7% percent of all tumors found in male dogs occur in the testicles. Among the most common and perhaps the best studied among these is the seminoma, a testicular tumor that arises from the germinal epithelium (the cells of the testicle that produce sperm).

Seminomas account for approximately 42% of all testicular tumors. They may occur on one side or on both (in approximately 18% of cases).

While the majority of these exhibit benign activity (they're rarely locally invasive and spread in less than 10% of cases), they may produce estrogen. In these rare cases, changes related to feminization will occur among affected dogs.

It's important to note that 34% of seminomas are found in testicles that are undescended (cryptorchid). In fact, unilaterally cryptorchid dogs have a 16-fold risk of developing a seminoma in their undescended testicle (compared to their descended testicle). While most testicular tumors tend to occur in dogs over the age of six, it's interesting to note that in unilaterally cryptorchid dogs, a seminoma in the descended testicle tends to be observed in younger dogs.

In addition to cryptorchidism, seminomas may also be associated with prostatic disease and enlargement, circumanal gland hyperplasia, perianal tumors (such as perianal adenomas and perianal adenocarcinomas), and perineal hernias.

With treatment, the prognosis for most dogs with this tumor type is considered excellent.

Symptoms and Identification

Scrotal swelling and palpation of a mass in the testicle or inguinal area is the most commonly cited sign of a testicular tumor. But because of its correlation with cryptorchidism, seminomas in undescended testicles may not become apparent until dogs have obvious signs associated with an abdominal mass.

Feminization may be observed in rare cases. A tell-tale stripe of reddened skin between scrotum and prepuce may be apparent in these dogs.

The following are typical approaches to identification of these tumors:

  • Scrotal palpation (these masses are typically easy to palpate)

  • Rectal examination (to feel intra-abdominal masses)

  • Abdominal X-rays

  • Abdominal ultrasound

  • Exploratory surgery (to observe and possibly biopsy the nearby lymph nodes for possible tumor spread)

  • Sperm analysis (sperm abnormalities can result from these tumors)

  • Chest X-rays

  • Biopsy upon castration (fine-needle aspiration and biopsy aren't typically recommended before castration as these can result in permanent damage to the testicular tissue that may obscure disease progression)

Affected Breeds

While all breeds of dogs are susceptible to seminomas, the Siberian Husky, Old English Sheepdog, Norwegian Elkhound, Great Dane, Keeshond, English Bulldog, Weimaraner, Scottish Terrier and Fox Terrier are predisposed.


Seminomas are considered highly treatable. Castration is the treatment of choice. This, of course, includes the removal of any undescended testicle. In these cases, castration may be a bit more complicated than for the average dog since dogs with testicular tumors may require the removal of the overlying scrotal skin.

Radiation therapy combined with chemotherapy has successfully been used in dogs with metastatic or invasive seminomas to yield a complete clinical cure.

Veterinary Cost

The veterinary cost of seminomas is typically relegated to the tests and surgery required to identify and treat them, respectively.

Because most cases are fairly straightforward, expenses tend to run under $500 for diagnosis and under $1,000 for treatment. In metastatic or otherwise complicated cases, however, expenses can increase dramatically depending on the need for advanced surgery techniques, radiation or chemotherapy.


There is no known means of prevention for seminomas, indeed for any testicular tumor, save early castration. The pros and cons of castration should be discussed with a veterinarian, ideally in advance of adolescence. Since cryptorchid pets are more at risk, they should ideally be castrated early. Furthermore, given the hereditary nature of testicular tumors, affected dogs should be removed from the gene pool immediately.


Bush, J.M. Gardiner, D.W. Palmer, J.S. Rajpert-DeMeyts, E. Veeramachaneni, D.N.R. Testicular germ cell tumours in dogs are predominantly of spermatocytic seminoma type and are frequently associated with somatic cell tumours. International Journal of Andrology. Volume 34, Issue 4pt2, pages e288-e295, August 2011

Dhaliwal RS, Kitchel BE, Knight BL, et al. Treatment of aggressive testicular tumors in four dogs. J Am Anim Hosp Assoc 35: 311-318; 1999.

Grieco V, Riccardi E, Greppi GF, et al. Canine testicular tumours a study on 232 dogs. J. Comp Path 138: 86-89, 2008.

Looijenga LH1, Olie RA, van der Gaag I, van Sluijs FJ, Matoska J, Ploem-Zaaijer J, Knepfle C, Oosterhuis JW. Seminomas of the canine testis. Counterpart of spermatocytic seminoma of men?Lab Invest. 1994 Oct;71(4):490-6.

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