Testicular Tumors in Dogs

Testicular tumors are one of the most common types of tumor found in male dogs who have not been neutered. If your male dog isn't neutered, he's at high risk for developing testicular tumors. Here's what you should know.

Risk Factors for the Development of Canine Testicular Tumors

Testicular tumors are most common in geriatric animals, but they can occur in dogs of any age. Testicular tumors occur in dogs of all breeds, and vets aren't yet sure what causes them. 

Dogs with undescended testicles (cryptorchidism) are far more likely to develop testicular tumors than dogs with normally descended testicles. Cryptorchid dogs should have their undescended testicles removed as soon as possible to eliminate the risk of testicular tumor development later in life.

Types of Testicular Tumors in Dogs

Dogs usually develop one of three kinds of testicular growths or tumors. They are:

  • Seminomas, which cause swelling in the scrotum, testicles or abdomen
  • Interstitial cell tumors, which typically don't spread
  • Sertoli cell tumors, which cause a range of symptoms and can spread to other organs and body parts

Symptoms of Testicular Tumors in Dogs

Symptoms of testicular tumors in dogs will vary depending on the type of tumor your dog develops. Sertoli cell tumors in the canine testicle cause a wide range of symptoms. These tumors cause the testicles and scrotum to swell. If the dog in question has undescended testicles, the swelling will occur not in the scrotum, but in the part of the body where the undescended testicles are located. 

As many as half of Sertoli cell tumors produce estrogen, so dogs with this type of tumor will display symptoms of the disease known as hyperestrogenism. They'll develop an enlarged prostate, enlarged nipples and mammary glands, and may become anemic. They may lose hair from both sides of their bodies, in the same pattern. These dogs could become sexually attractive to other dogs of the same gender. Sertoli cell tumors can, in rare cases, spread to other parts of the body, including the lungs and brain.

Seminomas cause swelling of the abdomen, scrotum and testicles. In rare cases, this type of tumor can produce estrogen and cause the symptoms of hyperestrogenism discussed above. In about five percent of cases, this type of tumor can spread to other parts of the body.

Interstitial cell tumors generally don't cause any symptoms at all. If they do cause symptoms, then those symptoms are almost always mild. Interstitial cell tumors are usually discovered in the course of a routine examination. Most vets don't consider this type of tumor to be a serious condition.

Treating Canine Testicular Tumors

Canine testicular tumors don't often spread to the rest of the body, so treatment is generally as simple as surgical castration. In 85 to 95% of cases, castration is the only treatment necessary for testicular tumors in dogs. Unless the cancer has already spread, the prognosis will be very good. In the rare case in which the cancer spreads, your vet will give a more guarded prognosis; however, chemotherapy has successfully treated many dogs with metastasized testicular cancer.