Testicular Tumor (Seminoma) in Dogs

PetMD Editorial
Written by:
PetMD Editorial
Published: April 19, 2010

Benign Tumor of Testis in Dogs

Seminoma is a unilateral, single, often benign (not recurrent or progressive) tumor of the testis; however, malignant forms of the tumor have been reported in rare cases. It is the second most common tumor of the testis in male dogs, typically affecting older dogs (over the age of four). Typically measuring less than two centimeters in diameter, a seminoma often causes no clinical symptoms in the affected dog and is therefore difficult to identify.

Symptoms and Types

Although seminomas rarely causes any clinical symptoms in the animal, some dogs exhibit pain due to pressure from the growing tumor. In a few cases, the testicular mass can be palpapated. Even rarer still, some tumors can become malignant and metastasize to other parts of the body.


Seminomas develop due to cryptorchidism, a fetal abnormality which occurs when one or both testes fail to descend into the scrotum from where they develop in the abdomen.


Your veterinarian will perform a thorough physical examination, searching for a testicular mass and whether or not it is palpable. Dogs with a seminoma may exhibit pain or abnormally large testis. Typically, laboratory tests such as complete blood count, biochemistry profile, and urinalysis are within normal ranges, although an ultrasound of the testicular tissue may reveal a mass. In these cases, your veterinarian may recommend performing a tissue biopsy of the testicular mass for further evaluation. If this is not possible, castration may be required to confirm the diagnosis.



Removal of the tumor is the treatment of choice, which is best accomplished by castrating the dog. If the tumor is cancerous or has metastasized to other parts of the body, however, your veterinarian may recommend chemotherapy.

Living and Management

In general, the overall prognosis of dogs that undergo castration is excellent. But this is dependent on the whether the tumor is benign or malignant.

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