A seminoma is a tumor of the testicle that involves the germinal cells that normally produce sperm cells. The majority of seminomas are benign, usually slow growing, and not invasive. Five to ten percent are malignant.

The specific cause of tumor development is unknown, but dogs that are cryptorchid, which means that one testicle has not descended into the scrotum, are ten times more likely to develop a tumor. Cyrptorchid testicles are generally within the abdomen, but may be under the skin in the inguinal area, or the area of the body where the hind leg meets the body wall. Cryptorchid testicles are also much more likely to be malignant.

Breeds at greater risk of cryptorchidism such as Weimaraners and Shetland sheepdogs are more likely to develop a seminoma. Boxers are at increased risk of all testicular tumors regardless of cryptorchidism.

Dogs are more likely to develop a seminoma as they age.

Seminomas rarely may produce elevated androgen (male sex hormone) levels or lead to a male feminization syndrome. Seminomas can also cause a severe bone marrow disorder (bone marrow hypoplasia). This is also an unusual occurrence. Most dogs with seminomas are not ill, and many are simply found during a routine physical examination.

What to Watch For

Soft swellings in one or both testicles

A single enlarged testicle or asymmetric testicles

Generalized scrotal enlargement

Infertility in the breeding stud dog

Enlargement of the mammary glands

Symmetrical hair loss

Hyperpigmentation (darkening or turning black) of the skin

Decreased libido and a pendulous prepuce

Excessive androgen secretion may also produce signs of prostatic and perianal disease, or diseases around the anus

Diagnosis

A good physical examination including palpation of the testicles

Complete blood count (CBC)

Platelet count

Biochemical profile

Urinalysis with or without culture and sensitivity

Chest and abdominal X-rays

Abdominal and or scrotal ultrasound

Fine needle aspiration

Biopsy and histopathology (microscopic analysis of tissue) of removed testicle or tumor

Treatment

Surgical removal of the involved testes (orchiectomy)

Chemotherapy if the tumor has metastasized (spread)

Radiation therapy

Supportive care if associated disease conditions are present

Home Care and Prevention

Watch the incision daily for any sign of swelling or discharge. The scrotal sack may be slightly swollen post-operatively, but this should slowly resolve within a week or two. If skin sutures are used, they should be removed in 7 to 10 days.

If your dog begins to lick the area excessively, an Elizabethan collar may be required to prevent licking at incisions.

Seek veterinary care if your dog has a fever or is feeling ill post-operatively. If your dog had bone marrow hypoplasia due to the seminoma, close monitoring of blood tests will be required.

An excellent preventive measure is to have your dog neutered (castrated) at an early age.