Testicular Tumor (Leydig Cell) in Cats

By PetMD Editorial on Feb. 3, 2009

Tumor of the Interstitial Cell of the Testicle in Cats

The Leydig cell tumor (LCT) is a rare and typically benign tumor that affects older male animals. These tumors are located in the testis and are made up from the cells that release the testosterone hormone into the connective tissue of the testicles. This type of tumor may occur singularly, or in multiples, measuring about 1-2 cm in diameter and spherical in shape. LCTs can be felt as a mass, causing soft swelling of the affected testis. It is classified as a sex-cord stromal tumor, meaning that the tumor issues from the connective tissues of the sex-cords of the testis. This disease is relatively rare in cats.

Symptoms and Types

  • One or more round masses (1-2 cm in diameter) in a testicle
  • There are generally no symptoms with this type of tumor, unless it is actually a Sertoli cell tumor (cells which help nourish spermatids as they transform into spermatozoa in the testicles)
  • Signs of a Sertoli cell tumor:
    • Feminization (from secretion of estrogen)
    • Bone marrow underdevelopment


The cause of LCT is unknown, but a retained testicle (usually in the abdomen) may predispose cats to Leydig cell tumor formation.


Your veterinarian will perform a complete physical exam, palpating (examination by touch) your cat's testicles to examine the size, location, and consistency of the tumor. You will need to provide a thorough history of your cat's health, with a description of symptoms, if any, and their time of onset. Usually a blood chemical profile, complete blood count, and urinalysis will return as normal, but there may be various reductions of cells in the circulating blood if there is an excess of estrogen. Blood serum should also be tested for estradiol, an estrogenic hormone, and testosterone concentrations. Usually estradiol levels will be high, while testosterone levels will be low. Your veterinarian may also take a fine needle sample of fluid (aspirate) from the tumor to check for abnormalities in the cells, by use of a cytological (microscopic) examination

Tumors smaller than 3 cm in diameter will appear black on ultrasound imaging. However, tumors greater than 5 cm have a black and white blotched appearance on ultrasound.


Affected cats should be neutered, and the tumor(s) removed and sent for histopathologic analysis – examination of the diseased tissue. If your cat shows signs of bone marrow underdevelopment, your veterinarian may prescribe medical therapy to reverse it.

Living and Management

Infection after surgery is always a cause for concern, and care must be taken to keep the surrounding area clean. You will need to observe any post-operative surgical incisions for swelling, redness or oozing. Infections can get complicated quickly. If any of these conditions are present, or if you have any questions, contact your veterinarian for further advisement.

If you are concerned about your ability to prevent your cat from getting its surgical site dirty, cage rest can be used to hold your cat in an enclosed environment until the sutured skin has healed adequately. An Elizabethan collar can also be used to prevent your cat from licking or biting at the healing skin – which may itch as it heals.

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