Dog: Testicular Tumors

General information

Other common/scientific names: Sertoli cell tumors, seminomas, Leydig (interstitial) cell tumors

Testicular tumors are most common in intact (not castrated) older male dogs. Fortunately, the overall incidence of testicular tumors in dogs is low because of the large numbers of dogs that are castrated.

The three common types of testicular tumors are: Sertoli cell tumors, seminomas and Leydig (interstitial) cell tumors. While these tumors are composed of different cell types, they are often treated similarly and therefore commonly grouped together as testicular tumors. Testicular tumors in dogs are rarely malignant and metastasis (spread of cancer) is rare.


The exact cause of tumor development is unknown. However, studies have shown that dogs with a undescended testicle (cryptorchidism) are 13 times more likely to develop testicular cancer in the retained testicle.

Cardinal symptom

Enlarged testicle(s)


An enlarged testicle and swollen scrotum are common signs. Sertoli cell tumors tend to produce estrogen leading to the condition known as male feminizing syndrome. This syndrome can produce enlarged mammary glands, symmetrical (even) hair loss, increased skin pigmentation, pendulous penile sheath and atrophy of the non-cancerous testicle.

Abb. GGLXINNR: Testicular Tumor.
This is a photograph of a large, easily visible, testicular tumor.


Diagnosis is based on physical examination. Ultrasonography should be performed on any dog with an enlarged testicle to rule out orchitis. Dogs suspected of a testicular tumor should have abdominal and chest radiographs to check for spread of the cancer. Dogs exhibiting systemic disease should also have a complete blood count (CBC), serum biochemistry tests and urinalysis completed.

Abb. GGLXP708
Abb. GGLXP708: Ultrasonography of testicular tumor.
This is a digital ultrasound image of a testicular tumor.


Treatment usually consists of surgical castration. Because of the success with testicular removal and the low rate of metastasis, castration is usually the only treatment needed. A sample of the tumor should be submitted to a laboratory for identification of the cells. Dogs which have metastatic disease may benefit from chemotherapy.


The prognosis for testicular cancer in dogs is usually good. The clinical signs of feminization usually resolve with removal of the tumor. Dogs with malignant tumors which have spread to other areas have a poor prognosis.


Testicular cancer is prevented by castration.

Update version: 4/24/2014, © Copyright by
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