Testicular Tumor (Leydig Cell) in Dogs

A Leydig cell tumor (LCT) is a tumor of the testicle. It develops from Leydig cells — the cells in the testicles that release the male hormone, testosterone. It is a rare and benign tumor made up from the cells that release the testosterone hormone in the connective tissue of the testicles. It leads to feminizing syndrome. This type of tumor may occur singularly, or in multiples.  The tumor mass is located in the testis, causing soft swelling of the affected testis. It measures about 1-2 cm in diameter and is spherical in shape. 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 condition affects older male dogs.

Common symptoms are:

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


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