The most prevalent testicular tumours are Sertoli cell tumours, Leydig cell tumours and seminomas.

Sertoli cell tumours originate from cells that line the sperm canals and support the formation of sperm.

Leydig cell tumours originate from interstitial cells near the sperm canals and produce testosterone.

Seminomas originate from germ cells in the sperm canals.

Behaviour

In the testes, tumours can develop from different cell types, each with their own properties. Depending on the involved cell type, the tumour can behave differently (e.g. by disturbing the hormone balance). Most dogs with testicular tumours are asymptomatic and a testicular mass is discovered as an incidental finding. If clinical signs are apparent, they are the result of metastases or a disturbed hormone balance.

• Sertoli cell tumours represent 8-33% of all testicular tumours. Fifty percent of Sertoli cell tumours produce too much oestrogen. This can lead to symmetrical bald spots, swelling of the mammary glands, milk production and / or attraction of other male dogs to even spontaneous bleeding and a greatly increased risk of serious infections. This tumour type spreads in less than 15% of cases.
• Seminomas represent 33-52% of all testicular tumours. This tumour type mainly takes up space, rarely overproduces oestrogen and spreads in less than 15% of the cases.
• Leydig cell tumour represent 33-50% of all testicular tumours. This tumour type manifests generally only by taking up space, rarely overproduces oestrogen and very rarely metastasizes.

Non-descended testes have higher chances of tumoural degeneration into Sertoli cell tumours and seminomas. The overall prevalence for testicular tumours in intact dogs is 7%.

Prevalence

These tumours are most common in older male dogs around the age of 10 years. Over 60% of undescended testes tumours have been identified in middle-aged dogs (6-10 years).

Breed predisposition

A higher risk for the development of testicular tumours has been reported for Afghan Hound, Boxers, Collie, Maltese dog, Shetland sheepdog, and Weimaraner vs other dogs.

Physical examination of intact male dogs, and particularly older dogs, should always include palpation of the testicles for masses and/or asymmetry. When the veterinarian detects irregularities, a rectal examination can be performed to identify further abnormalities such as swelling of the local lymph nodes.

The veterinarian can use ultrasound to inspect the abdominal cavity / the testicle and check whether there is an undescended testicle. If this is the case, the veterinarian examines whether it has an abnormal shape and if enlarged lymph nodes are present. Ultrasound-guided fine needle aspirates of testicular tumours are hardly performed as they may at best support a suspicion of neoplasia.

In dogs with clinical signs of hormone imbalance, the veterinarian can draw blood to check for an altered testosterone/oestradiol ratio.

Surgery

Removal of the testes and scrotum is always recommended to treat testicular cancer. Clinical signs of disturbance in the hormone balance disappear automatically within 1-3 months after the surgical intervention. If these symptoms persist, this may indicate the presence of metastases. Dogs with a suboptimal function of the bone marrow due to an excess of oestrogen require close monitoring during and after the surgical intervention for complications requiring medical product intervention with blood products and/or antibiotics.

Chemotherapy and radiotherapy

In case of metastases, chemotherapy or radiation can be considered, although their effect has so far not been described extensively enough to be able to draw any solid conclusions.

The prognosis is generally very good after surgery. When the bone marrow is suppressed by a disturbance of the hormone balance, the dog must be monitored very carefully. After all, this bone marrow suppression can be irreversible and life-threatening.