Leydig cell tumors, also known as interstitial cell tumors, are small growths that develop on the testes of intact male dogs. They are usually benign and often have no apparent symptoms other than the tumor itself. They are made up of an overgrowth of interstitial cells of Leydig which are found normally in the testicle. Leydig cells produce testosterone when stimulated by another hormone, lutropin. Although other testicular tumors are likely to cause an increase in estrogen in the affected animal, Leydig cell tumors do not normally cause an upsurge in that hormone. Surgical removal of the testes is the usual course of action as well as some of the surrounding tissues.

Leydig cell tumors, also referred to as interstitial cell tumors, are small benign growths that can develop on the testes of intact male dogs.

Symptoms that may indicate the presence of a Leydig cell tumor could include:

Leydig cell tumors in dogs tend to have very few symptoms. This variety of tumor has little to no effect on estrogen levels, so symptoms related to increased estrogen levels indicative of other forms of testicular cancer would be absent. 

Types 

Three types of cancer will commonly develop on the testes of intact male dogs.

Other less common cancers or growths that can affect the testes can include embryonal carcinomas, gonadoblastomas, granulosa cell tumors, hemangiomas, lymphomas, mucinous adenocarcinomas, rete testis, sarcomas, and teratomas.

The origins of any type of cancer are ambiguous but there are some conditions that may increase the likelihood of testicular cancers to develop in your canine. 

Dogs with undescended testicles are more than ten times more likely to develop testicular cancer than dogs with normal testes development, and tumors that are located on undescended testicles are more likely to behave malignantly.

Your veterinarian is likely to start with a verbal history from you as well as a physical examination of the masses or lesions and the area surrounding them. A tissue sample will also be obtained so that it can be more closely examined. A complete blood count, biochemistry profile, and urinalysis will be obtained to reveal any underlying or concurrent disorders or diseases. The increase in the levels of testosterone instead of estrogen in the blood will also help differentiate a Leydig cell tumor from the other testicular tumors. 

Depending on the size and the placement of the tumor the veterinarian will use either a fine needle aspiration or full excision technique to take a sample of the affected tissue. The biopsy of this tissue will reveal the source of the growth. An ultrasound of the abdomen and testicle area may also be recommended to get a better idea of the placement, size, and shape of the testes within the body.

Surgical removal of the testicles is generally the first course of action with any testicular tumors. It is normally recommended that the scrotal skin be removed at this time to avoid pain from post-operative swelling and it is often necessary to remove a portion of the spermatic cord as well. If the testicle or testicles have not dropped the surgery may involve incisions into the abdomen to access them for removal. Surgery is completely curative for most Leydig cell tumors as the metastatic rate is low. In the rare event that the tumor spreads additional more aggressive therapies may be required to prevent reoccurrence. Radiation therapy and chemotherapy treatment and the overall outcome becomes more guarded. Chemotherapy has been endorsed on its own for these growths for rare situations in which surgery is not a viable option.

After any surgery, it is essential to keep the site clean and free from dirt and debris. You will need to keep your pet from interfering with the site, and examine it regularly over the next two or three weeks for swelling, bleeding or pus. Keeping the recovering patient in a calm, quiet environment will help speed healing, as will having appropriate food and water within their reach.  Specialized feeding and care instructions may be given by your veterinarian to facilitate healing and you may be requested to bring your pet back in to evaluate healing in about ten to fourteen days.