What Are Testicular Tumors in Dogs?

Testicular tumors are among the most frequently diagnosed tumors in older, unneutered male dogs. These dogs retain both of their testicles, which serve the dual purpose of producing sperm for reproduction and synthesizing important male hormones like testosterone.

A tumor arises when cells begin to grow abnormally, multiplying uncontrollably and forming an unusual mass of tissue. Without timely and appropriate treatment, this abnormal growth can increase in size. Testicular tumors are relatively uncommon overall, mainly because many male dogs are neutered at a young age before tumors have the opportunity to develop.

Tumors can be either benign or malignant. A benign tumor means it is non-cancerous and has not spread beyond its original spot, such as within the testicle itself. In contrast, a malignant tumor is cancerous and can metastasize—spreading to other organs like the lungs or lymph nodes after originating in the testicle.

Types of Testicular Tumors in Dogs

Male dogs can develop three main types of testicular tumors:

• Seminoma: These tumors develop from the germ cells, which are responsible for producing sperm.
• Interstitial Cell Tumors: These arise from the cells that generate testosterone, the key male hormone.
• Sertoli Cell Tumors: These originate from Sertoli cells that provide nourishment and support to developing sperm.

Other less common tumor types such as lipomas, fibromas, and hemangiomas can occur but are rarely seen in dogs.

Symptoms of Testicular Tumors in Dogs

The signs of testicular tumors in dogs can be subtle and vary based on the tumor type and location. For dogs with long coats, hair can easily mask physical changes, making tumors harder to detect. Typically, tumors are discovered during a physical examination when the vet palpates the testicles.

Symptoms to watch for include:

• One or more enlarged lumps on one or both testicles
• Noticeable difference in size between testicles
• Swelling of the scrotum (the skin sac housing the testicles)
• Enlarged mammary glands and nipples
• Drooping of the prepuce (the skin sheath covering the penis)
• Localized hair loss and darkening of the skin in the scrotal area
• Squatting to urinate in a manner more typical of female dogs
• Infertility issues in breeding males
• Attraction of other male dogs due to elevated estrogen levels

If the tumor is cancerous and has spread beyond the testicles, additional signs may emerge, such as:

• Unusual lethargy or persistent tiredness
• Noticeable weight loss
• Reduced appetite or loss of interest in food
• Difficulty breathing or labored respiration
• Persistent coughing
• Trouble urinating or defecating caused by enlarged lymph nodes or compression of the prostate gland

What Does a Testicular Tumor Look Like?

Normally, testicles have an egg-shaped appearance and rest within the scrotum, located between the upper thighs and behind the penis. It’s common for one testicle to sit slightly higher than the other.

Signs that may indicate the presence of a tumor or other abnormalities include:

• Soft or firm swelling on one or both testicles
• Enlargement of the scrotum
• One testicle noticeably larger than the other
• Asymmetrical testicles
• Testicles that feel irregular, lumpy, or bumpy to the touch
• Signs of pain or discomfort when the testicles are palpated

Causes of Testicular Tumors in Dogs

While the exact reason why some dogs develop testicular tumors isn’t fully understood, factors such as genetics, environmental exposure, and certain breed predispositions may increase the risk.

Age is a significant contributor. Although dogs of any age and breed can develop these tumors if unneutered, they occur most often in dogs older than 10 years. Certain breeds, including German Shepherds, Afghan Hounds, Boxers, Weimaraners, and Collies, show a higher incidence of testicular tumors.

How Veterinarians Diagnose Testicular Tumors in Dogs

Testicular tumors are sometimes discovered incidentally during routine physical exams when a veterinarian detects a nodular mass or changes in testicular texture. Occasionally, a vet may find only one testicle present, a condition called cryptorchidism, which affects about 13% of male dogs.

If your dog exhibits signs of illness that suggest a tumor, your veterinarian may recommend diagnostic imaging such as chest or abdominal X-rays, or an ultrasound of the abdomen and scrotum to locate any masses. Blood tests, urinalysis, and a rectal exam may also be performed to identify other underlying conditions.

An accurate diagnosis of the tumor type is only possible after surgery. The removed tissue is sent to a veterinary pathologist for microscopic examination to determine whether the tumor is benign or malignant and to specify its kind.

For breeding dogs, vets sometimes prefer to take a small biopsy or perform a fine needle aspirate—a minimally invasive procedure that collects tissue samples—to ascertain the tumor type without resorting immediately to neuter surgery.

Treatment of Testicular Tumors in Dogs

The cornerstone of treatment for testicular tumors in dogs is surgical removal of the affected testicle(s). When tumors are malignant and have spread beyond the testicles, additional therapies such as chemotherapy or radiation may be considered to control cancer’s progression.

Some dogs with underlying health problems—like heart murmurs, respiratory difficulties, or obesity—may face increased risks during anesthesia and surgery, complicating treatment options.

If the tumor is benign, small, and slow-growing, your veterinarian may recommend close monitoring to watch for signs like rapid enlargement, pain, bleeding, or interference with mobility. However, surgical removal is generally advised before tumors cause noticeable discomfort or complications.

Recovery and Management of Testicular Tumors in Dogs

Most testicular tumors have a low risk of spreading if cancerous, and surgical removal often provides a complete cure.

Sertoli cell tumors and seminomas carry less than a 15% chance of metastasis, while interstitial cell tumors are usually benign and seldom spread beyond the testicles. However, tumors originating from other urinary or reproductive organs may sometimes spread to the testicles, warranting thorough checks for cancer elsewhere.

For tumors that have metastasized, the prognosis varies depending on tumor type, location, and available treatments, often making the outlook more guarded.

Post-surgery, your dog will likely need to wear an Elizabethan collar (E-collar) to prevent licking or chewing at the incision site, which could lead to infections or wound complications.

Recovery closely resembles that of a standard neuter operation. Your dog should be kept calm with limited activity—no running, jumping, or vigorous play—for 10 to 14 days. Active dogs might need to be confined to a small space or crate to help them rest and heal properly.

Daily inspection of the surgical site is important. Look for signs of redness, swelling, heat, discharge, or foul smells that might suggest infection. Keep the incision site dry and avoid bathing or swimming until your veterinarian confirms full healing. Follow-up visits may be scheduled, especially if the tumor was malignant, to monitor your dog for any signs of recurrence.

Prevention of Testicular Tumors in Dogs

The most effective way to prevent testicular tumors in male dogs is through early veterinary examinations and timely neutering. Depending on your veterinarian’s advice and your dog’s breed, neutering can often be safely performed as early as two months of age.

For larger breeds, neutering may sometimes be delayed until they finish growing (between 9 to 15 months) to lower risks of certain cancers and joint problems later in life.

Are testicular tumors in dogs painful?

Not always. Many dogs with testicular tumors do not show clear signs of pain. However, as a tumor grows and places pressure on surrounding tissues, discomfort or pain may develop.

How common are testicular tumors in dogs?

Testicular tumors are the most prevalent type of tumor found in older, unneutered male dogs. While all breeds and ages can be affected, these tumors are not widespread overall, thanks to the common practice of early neutering.