Tumors of the Testicles
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 undescended testicle).
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.
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 suppression.
Ultrasonography is particularly useful in locating undescended testicles and determining whether a scrotal mass is a tumor, abscess, testicular 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 testicles.
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 exposure.
Transmissible venereal tumors are solitary or multiple tumors that usually appear as cauliflowerlike growths or as nodules on a stalk. The growths may be multinodular and/or ulcerated.
In females, transmissible venereal tumors develop in the vagina and on the vulva. In males, they occur on the penis. Other locations in both sexes include the skin of the perineum, face, mouth, nasal cavity, and limbs.
Transmissible venereal tumors are considered low-grade cancers. They do have the potential to metastasize, although this is rare.
Treatment: Chemotherapy is the recommended treatment. The drug of choice is vincristine, given weekly for three to six weeks. Radiation therapy is also highly effective; most dogs are cured after a single dose.
Surgery is not considered an effective treatment because it is associated with a high rate of local recurrence. Dogs and bitches not intended for breeding should be neutered or spayed.
The vaginal and vulvar areas are the most common sites for tumors of the female genital tract. These tumors tend to occur in older, sexually intact females, at an average age of 10 years. Benign tumors include leiomyomas, lipomas, and transmissible venereal tumors. They are often found on a narrow base or a long stalk.
Malignant tumors in this area are rare. They include leiomyosarcomas, squamous cell carcinomas, and mast cell tumors. Malignant tumors grow locally, infiltrate surrounding tissue, and become quite large. They rarely metastasize.
Signs include vaginal discharge or bleeding, a mass protruding through the vulvar lips, frequent urination, and excessive licking at the vulva. Large vaginal tumors can cause swelling and deformity of the perineum, block the birth canal, and cause problems in whelping. Note that a mass protruding through the vulva of a bitch in heat is most likely to be due to vaginal hyperplasia.
Treatment: Surgical removal with a margin of normal tissue is the treatment of choice. Recurrence may follow removal.
Tumors of the Ovaries
Ovarian tumors are uncommon. Most cause no symptoms and are found incidentally during a spay operation. Occasionally, a tumor becomes large enough to produce a visible or palpable swelling in the abdomen.
Treatment: Removal of the ovaries by ovariohysterectomy (spaying) cures benign tumors. The cure rate for malignant tumors is about 50 percent. The addition of chemotherapy for metastatic tumors may extend the time the dog is in remission.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.