Testicular tumors are common in male dogs. Most affected dogs are
over 6 years of age, with a median age of 10. The majority of tumors occur in
undescended testicles-located in the inguinal canal or abdominal cavity. In
fact, tumors develop in up to 50 percent of undescended testicles. A swelling
or firm mass in the inguinal canal in a dog with an undescended testicle is
characteristic of a testicular tumor (although the mass may simply be the
Tumors in descended testicles are less common. The affected testicle is
often larger and firmer than its neighbor and has an irregular, nodular
surface. At times the testicle is normal size but feels hard.
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The three common testicular tumors in dogs are Sertoli cell tumors,
interstitial (Leydig) cell tumor, and seminomas. A small percentage of Sertoli
cell tumors and seminomas are malignant.
Some Sertoli cell tumors produce estrogen, which can result in feminization
of the male with enlargement of the mammary glands, a pendulous foreskin, and
bilateral symmetric hair
loss. A serious complication of high estrogen levels is bone marrow
Ultrasonography is particularly useful in locating undescended testicles and
determining whether a scrotal mass is a tumor, abscess,
torsion, or scrotal hernia. Fine needle aspiration biopsy provides
information on the cell type of the tumor.
Treatment: Neutering is the treatment of choice. This is curative in nearly
all cases, even when the tumor is malignant. For scrotal tumors in fully
descended testicles, the normal testicle can be left if future fertility is
desired. If one or both testicles are undescended, both testicles should be
removed, since the condition is heritable and the dog should not be bred. Signs
of feminization in Sertoli cell tumors may disappear after neutering-but this
is not always the case.
Prevention: Tumors of the testicles can be prevented by neutering dogs early
in life. It is particularly important to neuter all dogs with undescended
Transmissible Venereal Tumors
An unusual neoplasm called transmissible venereal tumor occurs in both males
and females. Tumor cells are transplanted from one dog to another, primarily
during sexual contact, but also through licking, biting, and scratching.
Transmissible venereal tumors tend to occur in free-roaming dogs, particularly
those living in urban areas. They appear within seven days of contact