Dog Testicular Tumors: Don't Wait — Symptoms, Causes, Neutering Treatment, and Prognosis

Oncology/CancerDiseasesMeongsiljang Veterinary Advisory Board

Testicular tumors are one of the most common malignant tumors in male dogs. Early detection and surgery are key to treatment.

What Are Dog Testicular Tumors?

A medical illustration highlighting the reproductive anatomy of a dog.

Testicular tumors in dogs arise from the tissues of the testicles. Common types include interstitial (Leydig) cell tumors, seminomas, and Sertoli cell tumors. Most of these tumors grow slowly and rarely metastasize, with fewer than 1% of cases resulting in death from the primary tumor. They primarily affect middle-aged and older male dogs. Some tumors, such as Sertoli cell tumors, secrete estrogen and can cause feminizing symptoms like mammary gland enlargement (gynecomastia) and hair loss. In the early stages, there are often no noticeable symptoms, and the condition is frequently discovered incidentally. However, caution is warranted if one testicle becomes swollen or if there is a noticeable size difference between the two. The risk is highest in dogs with cryptorchidism (undescended testicles). Early diagnosis and neutering (castration) are key to treatment, and veterinary textbooks emphasize neutering as an effective preventive and therapeutic measure.

What Are the Main Causes of Testicular Tumors?

While the exact cause of testicular tumors remains unclear, age and cryptorchidism (retained testicles) are known risk factors. Dogs with testicles retained in the abdomen are at the highest risk, so neutering is recommended for all cryptorchid dogs. Intact males remain at risk, and hormone-secreting tumors such as Sertoli cell tumors have been reported. Although some sources suggest higher incidence in terriers or small breeds, definitive breed-specific statistics are difficult to verify in standard textbooks, making cryptorchidism a more significant risk factor than breed. Since most testicular tumors are easily cured through neutering, early surgery is recommended for both preventive and therapeutic purposes. Early intervention significantly improves prognosis.

A veterinarian examining a puppy’s testicles by gently palpating the area.

Check for Key Symptoms and Signs

Testicular tumors are often asymptomatic in the early stages or discovered incidentally. However, if you notice any of the following signs, it’s a good idea to have your pet checked.

Asymmetry and swelling in the testicular area: The affected testicle may enlarge while the opposite one atrophies, leading to noticeable size differences between the two sides or a hardened texture.

Feminization signs: Tumors that secrete estrogen can cause symptoms such as hair loss and swelling of the nipples and mammary glands (gynecomastia).

Anemia and bleeding tendencies: Excess estrogen can suppress bone marrow function, potentially resulting in pale gums or pinpoint bleeding (petechiae).

Prostate-related symptoms: Hormonal changes can cause prostate enlargement, which may lead to difficulty defecating or constipation.

If you observe any of these symptoms, consider the possibility of a testicular tumor and schedule a veterinary examination.

A medical illustration comparing normal and abnormal testes.

When to Visit the Vet Immediately

If the testicular area swells rapidly, your dog shows severe pain, or is unable to defecate at all, it’s an emergency. In such cases, contact your veterinarian immediately for a consultation and examination.

Diagnostic Tests for Accurate Diagnosis

Testicular tumors are suspected when physical examination and palpation reveal testicular asymmetry or masses. Ultrasound is used to evaluate testicular size, shape, and margins, as well as to check for intra-abdominal cryptorchid testes, prostate involvement, and metastasis. However, ultrasound alone cannot definitively determine the tumor type; therefore, ultrasound-guided fine-needle aspiration (FNA) or biopsy is performed to collect cells or tissue samples for differentiation among types such as interstitial cell tumors, seminomas, and Sertoli cell tumors. Complete blood count (CBC) analysis helps identify bone marrow suppression signs—such as anemia, leukopenia, or pancytopenia—that may occur with estrogen-secreting tumors. If metastasis is suspected, abdominal ultrasound and thoracic radiographs are helpful. According to veterinary textbooks, accurately determining the tumor type and presence of metastasis forms the foundation for developing a treatment plan. Early detection improves treatment success rates.

A veterinarian examining a dog's testicles using ultrasound.

Treatment: Surgery Is the Most Effective Option

The most fundamental and effective treatment for testicular tumors is surgery. By completely removing the affected testicle through castration (neutering), testicular tumors—which rarely metastasize—can often be cured relatively easily. In fact, fewer than 1% of dogs die from primary testicular cancer. If a tumor is present in a descended testicle within the scrotum and accompanied by scrotal adhesions, bilateral orchiectomy may be performed along with scrotal removal. In cases where the tumor was secreting estrogen, removing the testicle eliminates the source of hormonal stimulation, often leading to improvement in feminizing symptoms. Additional treatments are considered only in the rare instances where metastasis is confirmed, and veterinary textbooks emphasize surgery as the cornerstone of treatment. Early surgery increases the likelihood of a cure.

A medical illustration highlighting the process of removing the testicles from a dog during surgery.

Home Care and Precautions

After surgery, provide a quiet environment to aid recovery and carefully manage your pet’s activity level. Administer all medications exactly as prescribed by your veterinarian, and check the surgical site daily for swelling, bleeding, or signs of infection. Walks should be temporarily restricted, and you must prevent your dog from running too soon. Since dogs that have had their testicles removed are no longer able to reproduce, it is essential to keep accurate surgical records for pet registration purposes. Veterinary behaviorists emphasize the importance of emotional stability during the post-operative period. Continue to monitor your dog’s appetite and any changes in elimination habits.

A puppy resting comfortably while recovering after surgery

Breed-Specific Considerations and Preventing Recurrence

Testicular tumors are most common in dogs with cryptorchidism (undescended testicles). Therefore, neutering is recommended for all dogs with undescended testicles. While it's difficult to find definitive statistics in textbooks stating that these tumors are more common in terriers or small breeds, testicular tumors can be relatively easily prevented and cured through neutering. According to veterinary textbooks, neutering (castration) is an effective preventive measure.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Can testicular tumors metastasize?

While it's not common, certain tumors like seminomas or Sertoli cell tumors can spread to lymph nodes or the lungs. On the other hand, interstitial cell tumors rarely metastasize, and overall, testicular tumors are not frequently known to spread. Still, early neutering surgery remains the most re

Can my dog get sick again after surgery?

Removing the testicles through surgery greatly reduces the chance of recurrence, making it relatively easy to achieve a cure. However, since other tumors can still develop, regular check-ups are important.

Can testicular tumors cause hair loss?

Yes, estrogen-secreting tumors (particularly Sertoli cell tumors) can cause feminizing symptoms, such as hair loss and swelling of the nipples and mammary glands.

Do testicular tumors cause pain?

Testicular tumors are often discovered incidentally, as they typically don’t cause pain. However, if the tumor grows large enough, it may cause discomfort. If your pet avoids having its testicles touched or reacts sensitively when you do, it’s a good idea to have it checked by a veterinarian.

Is there anything special I need to prepare before the surgery?

Just follow your veterinarian’s instructions for fasting and preparing for the procedure. Blood tests and a cardiac evaluation are typically required before surgery.

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References

[1] Heaton, C.M. et al. (2020). Clinical Evaluation of toceranib for treatment of apocrine gland anal sac adenocarcinoma in dogs. Journal of Veterinary Internal Medicine, 34(2), 873–881.

[2] BSAVA Manual of Canine and Feline Dermatology, 4th Ed. (2021). Anal sac neoplasia in dogs: diagnosis and management.

[3] Veterinary Surgical Oncology, 2nd Ed. (2020). Chapter on testicular tumors in dogs: incidence, pathology, and surgical outcomes.