Testicular Tumors

By Krista Williams, BSc, DVM, CCRP; Debbie Stoewen DVM, MSW, RSW, PhD; Christopher Pinard, DVM

What is a testicular tumor?

A testicular tumor is a tumor that develops from a disordered uncontrolled growth of cells within the testicles.

The three most common types of testicular tumors develop from germ cells (cells that make sperm), Leydig cells (cells that produce testosterone), and Sertoli cells (cells that help in the development of sperm):

  • Seminomas develop from germ cells
  • Interstitial cell tumors develop from Leydig cells
  • Sertoli cell tumors develop from Sertoli cells

Other types of tumors may develop from other cells within the testicles, but these types are rare. Testicular tumors are considered one of the most common tumors in older intact (not neutered) male dogs and are rare in cats.

What causes this cancer?

The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.

"Certain breeds of dogs may be more predisposed to the development of testicular tumors."

In the case of testicular tumors, cryptorchid pets [pets with undescended testicles (i.e., the testicles are retained within the abdomen or in the passage through the abdominal wall into the genital region)], have a tendency to develop Sertoli cell tumors and seminomas, but not interstitial cell tumors. Older cryptorchid dogs (greater than 6 years of age) have a much higher tendency to develop some form of testicular cancer; older dogs in general have a higher rate of developing these tumors.

Certain breeds of dogs may be more predisposed to the development of testicular tumors, including Boxer Dogs, German Shepherds, Afghan Hounds, Weimaraners, Shetland Sheepdogs, Collie Dogs, and the Maltese.

What are the clinical signs?

Most dogs with testicular tumors do not have any obvious clinical signs. Any clinical signs seen will vary depending on the type of tumor and the tumor location.

The clinical signs may be limited to the presence of a mass (or masses) within the affected testicle. Palpation (feeling with the fingers) of the scrotum may reveal a nodular enlargement of the testicle, unevenly sized testicles, or generalized swelling of the scrotum.

"Most dogs with testicular tumors do not have any obvious clinical signs."

Sertoli cell tumors can produce estrogen and a condition called hyperestrogenism. Hyperestrogenism can cause signs of feminization. This includes enlarged mammary glands and nipples, a pendulous prepuce, hair loss, and hyperpigmentation (darkening) of the skin. Excess estrogen can also affect the bone marrow, causing anemia (pale gums) and lethargy. Behavioral changes may include squatting to urinate (versus hiking a leg), reduced sex drive, and attraction of other male dogs.

In the rare case of a malignant tumor, the signs may be related to the organs to which the tumor has spread, and can include weight loss, decreased appetite, lethargy, or vomiting. If the tumor has metastasized (spread) to the lymph nodes near the urinary system or the prostate gland, signs may include difficulty urinating or defecating.

How is this cancer diagnosed?

This cancer is often suspected during a routine physical examination. Your veterinarian may find an abnormal testicle when palpating the testicles or may find only one testicle present, noting your pet to be cryptorchid. If your pet is experiencing any signs of illness, an abdominal ultrasound may be recommended to search for an abnormal mass (tumor) in the abdomen.

"This cancer is often suspected during a routine physical examination."

Testicular tumors typically are diagnosed post-surgically, after the surgical removal of the testicles (neuter operation). If the pet has retained testicles, this involves abdominal surgery to remove the affected undescended testicle(s). Pieces of the testicular tumor are submitted to a veterinary laboratory where they examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is not only helpful to make a diagnosis but can indicate how the tumor is likely to behave.

For breeding males, further diagnostic testing (instead of surgery) may be done to differentiate a suspected tumor from a less concerning condition of the testicle (e.g., a cyst). In these cases, a fine needle aspiration (FNA) may be pursued, possibly using ultrasound to guide the needle. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tissue of interest and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.

How does this cancer typically progress?

These tumors typically are a local problem, meaning they have a low rate of spread. Both Sertoli cell tumors and seminomas have less than a 15% chance of spread to lymph nodes or other organs. Interstitial cell tumors rarely spread.

However, because other cancers of the urinary or reproductive system may spread to the testicles, staging (searching for potential spread to other locations in the body) is imperative. This may include a rectal examination, bloodwork, urinalysis, and chest X-rays. In cases of cryptorchid pets, abdominal ultrasound or more advanced imaging (such as a CT scan) may be recommended to determine if any lymph nodes or organs are affected. If any lymph nodes are enlarged or feel abnormal, further sampling may be pursued to determine if spread is present.

What are the treatments for this type of tumor?

By far, the most commonly recommended treatment is surgical removal of the testicles. If there is evidence of spread elsewhere, chemotherapy and/or radiation therapy may be considered.

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