Testicular Tumors in Dogs

Published May 25, 2023
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What Are Testicular Tumors in Dogs?

Testicular tumors are among the most common tumors seen in older unneutered male dogs. These dogs still have both testicles, which make sperm for reproduction and also produce male hormones such as testosterone.

A tumor forms when cells grow abnormally, populating and dividing out of control, leading to an abnormal mass of tissue. The mass may grow and enlarge if not treated appropriately. Testicular tumors are not common, since many dogs are neutered at a young age.

Tumors may be benign or malignant. A diagnosis of a benign tumor means that it is not cancerous and has not spread, or metastasized, outside of its original location, such as beyond the testicle. A tumor is considered malignant when it is cancerous and has spread outside of its original location, such as a mass that started growing in the testicle, but then spreads to other organs like the lungs and lymph nodes.

Types of Testicular Tumors in Dogs

There are three types of testicular tumors in male dogs:

  • Seminoma—Develop from the cells that produce sperm, also known as “germ cells”

  • Interstitial cell tumors—Develop from the cells responsible for the production of testosterone

  • Sertoli cell tumors—Develop from sertoli cells, which nourish and support developing sperm

Other forms of testicular tumors such as lipomas, fibromas, and hemangiomas can develop, but these occur rarely occur in dogs.

Symptoms of Testicular Tumors in Dogs

Clinical signs of testicular tumors in dogs are not always obvious and can vary depending on the tumor type and location. Testicles are difficult to see in dogs with longer coats, since the hair may hide subtle changes. Testicular tumors are often found while palpating or feeling the testicles for anything unusual during a physical exam.

Signs may include:

  • One or multiple enlarged nodules seen or palpated in the affected testicle(s)

  • Uneven testicular size

  • Scrotal swelling (sac of skin housing the testicles)

  • Enlarged mammary glands and nipples

  • Sagging prepuce (sheath of penis) 

  • Hair loss and darkening of the skin

  • Squatting to urinate (like a female dog)

  • Infertility in a breeding male

  • Sexual attraction of other male dogs due to increased estrogen levels

If the tumor is cancerous and has spread beyond the testicle, you may see:

  • Lethargy (tiredness beyond the normal level)

  • Weight loss

  • Decreased appetite

  • Labored or difficulty breathing

  • Coughing

  • Difficulty urinating and/or defecating due to enlarged lymph nodes or prostate gland narrowing or blocking these passages

What Does a Testicular Tumor Look Like?

Normal testicles are egg-shaped and housed within the scrotum, which is located between the upper thighs and behind the penis. One testicle may be slightly higher than the other.

Changes to the testicles and/or scrotum that may indicate a tumor include:

  • Soft or firm swelling affecting one or both testicles

  • Enlarged scrotum

  • One testicle larger than the other

  • Asymmetry of the testicles

  • Irregular, lumpy, or bumpy testicles

  • Painful testicle(s)

Causes of Testicular Tumors in Dogs

While it is unclear why one dog may develop a testicular tumor over another, certain environmental, genetic, and breed predispositions may be risk factors.

Age is also a risk factor. While unneutered dogs of any age and breed can have testicular tumors, they occur most commonly in those over 10 years old. They are also common in breeds such as German Shepherd, Afghan Hound, Boxer, Weimaraner, and Collie.

How Veterinarians Diagnose Testicular Tumors in Dogs

A testicular tumor may be found incidentally during a physical examination. Your veterinarian may feel an abnormal nodule or consistency that differs from normal testicular tissue, or they may discover that your dog only has one testicle instead of two. One testicle in male dogs is common is known as cryptorchidism, and it occurs in approximately 13% of male dogs.

If your dog is showing signs of illness and your veterinarian suspects a tumor, chest or abdominal x-rays, or an abdominal and scrotal/testicular ultrasound may be recommended to look for a mass. Bloodwork, urinalysis, and a rectal exam may also be necessary to find any potential abnormalities.

The tumor type is diagnosed after surgery, when a sample of the abnormal tissue is sent to a veterinary pathologist for examination in a laboratory. This is important in diagnosing what type of tumor is present and whether it is benign or malignant.

If your dog is used for breeding, your veterinarian may opt to take a small biopsy of the abnormal tissue or a fine needle aspirate (a sample of tissue with a small needle) instead of neuter surgery to determine the type of tumor. 

Treatment of Testicular Tumors in Dogs

Surgical removal of the testicles is the treatment of choice for dogs with testicular tumors. If the tumor is cancerous and has spread beyond the testicles, therapies such as chemotherapy or radiation therapy may be used to target and stop the advancement of cancer.

Complicating factors such as significant underlying disease, a heart murmur, respiratory issues, or obesity can make a dog an unsuitable candidate for anesthesia and surgery.

If a tumor has been diagnosed as benign and is small and slow-growing, you may be able to monitor it until you notice negative changes such as enlargement, causing pain, breaking open and bleeding, or interfering with your dog’s ability to walk. Typically, tumors are removed long before they become uncomfortable for your dog.

Recovery and Management of Testicular Tumors in Dogs

Testicular tumors often have a low rate of spread if they are cancerous. Surgical removal of the testicles often cures the issue. 

Sertoli cell tumors and seminomas have less than a 15% chance of metastasizing, while interstitial cell tumors are usually benign and rarely spread beyond the testicles. Cancer originating in the urinary tract or other parts of the reproductive tract may spread to the testicles, so in these cases it is often necessary to search for spread in other tissues and organs. Tumors that have spread can leave a guarded prognosis for your dog, but this depends on the type of tumor, its location, and options for treatment.

After surgery, your dog may need to wear an Elizabethan collar (E-collar) to prevent licking and chewing of the surgical site. If your dog bothers his surgical incision, it may lead to an infection or the stitches popping open.

Recovery time is similar to a regular neuter surgery, where your dog should be kept in a calm and quiet environment with limited activity for 10-14 days. This means no running, jumping, or roughhousing. If your dog is normally active, he may need to be confined to a small room or crate to help him remain quiet and heal from surgery.

You should carefully inspect the surgery site every day, noting any redness, swelling, heat, discharge, or foul odor that may indicate an infection. Keep the incision clean and dry—this means no bathing or swimming until your veterinarian confirms that your dog has completely healed from surgery. Your veterinarian may request follow-up appointments if your dog’s tumor was diagnosed as cancer to monitor for any reoccurrence of the disease.

Prevention of Testicular Tumors in Dogs

The best way to prevent testicular tumors in your male dog is to have them examined by a veterinarian and neutered at an early age. Depending on your veterinarian’s recommendations and the breed of your dog, male dogs can be neutered as early as two months of age. Larger breeds may benefit from delayed neutering until they stop growing (9-15 months of age) to help prevent the development of certain cancers and joint issues later in life.

Testicular Tumors in Dogs FAQs

Are testicular tumors in dogs painful?

Testicular tumors in dogs may not be painful—which means your dog may not show any signs that something is wrong. However, swelling and pressure from a growing tumor may cause signs of pain.

How common are testicular tumors in dogs?

Testicular tumors are the most common tumor found in older, unneutered male dogs, although all breeds and ages can be affected. The good news is that it’s not widespread, as many dogs have already been neutered.

Featured Image: Adobe/natali_mis


Blue Pearl Specialists. “Testicular Tumors in Dogs,” BluePearl Pet Hospital, 15 June 2017.

Davidson, Autumn P. “Reproductive Disorders of Male Dogs – Dog Owners.” Merck Veterinary Manual, March 2023.

Gazin AA, Vatnikov YA, et al. Canine testicular tumors: An 11-year retrospective study of 358 cases in Moscow Region, Russia. Veterinary World. 2022 Feb;15(2):483-487.


Stacie Grannum, DVM


Stacie Grannum, DVM


When Dr. Stacie Grannum was five years old, a baby bird fell high from its nest, and she diligently cared for it. Despite her attempts to...

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