Testicular cancer is both an easily recognized and diagnosed disease. It is the second-most common cancer in intact older dogs; however, it can occur in intact male dogs of any age. Three types of tumors are grouped under the umbrella of testicular cancer: interstitial, Sertoli and seminoma tumors. The prognosis is a positive one for most dogs with testicular cancer as long as no metastases are present. This cancer can be prevented by castration.
Interstitial tumors generally are benign and do not cause symptoms associated with other cancer types. These tumors are typically round and less than an inch in diameter. They are not considered to be problematic. Interstitial tumors also are called Leydig cell tumors. Interstitial tumors often occur when a testicle has been retained.
Seminoma tumors will cause the testicle, scrotum, inguinal or abdominal areas to become swollen. They usually appear only in one testicle of the pair and are benign in up to 85 percent of cases. Malignant seminoma tumors may metastasize to other organs. These tumors are typically under an inch in diameter. They are the second most common type of testicular cancer in dogs.
Like seminomas, Sertoli tumors can cause swelling of the testicle or the scrotum or, if the testicle is retained, in the abdominal or inguinal areas. Unlike seminomas, Sertoli tumors are malignant in up to 14 percent of cases. Up to half of these tumors will cause feminization, as they produce excess amounts of estrogen. Malignant Sertoli tumors will metastasize to the adjacent lymph nodes, as well as to the abdomen, brain, lungs and thymus.
Testicular Cancer Symptoms
Cancerous testicles are often larger than normal-sized testicles and can be of different sizes. When they are swollen, the swollen tissue can be soft or firm. The dog’s scrotum also may be swollen. Intact males used as stud dogs may be infertile. Some tumors cause femininization syndrome, due to an excess of estrogen being produced. This syndrome can cause enlargement of the mammary glands, a shrunken penis and squatting to urinate.
Diagnosing and Treating Testicular Cancer
Physical examinations that include testicle palpation are vital to diagnosing testicular cancer. Biopsy of the tumor can determine if it is benign or malignant. Additional diagnostic tests include a complete blood count and a veterinary chemistry panel. X-rays of the chest and abdomen also should be done to determine if metastases are present.
Most dogs are successfully treated by castration. Both testicles generally are removed, even when only one testicle is affected. Chemotherapy is rarely used, due to the low incidence of metastases in canine testicular cancer. Feminization is usually reversed without further treatment after castration. Dogs with bone marrow involvement will be prescribed additional therapy to treat it.
Preventing Testicular Cancer
Neutering a male dog is the best form of prevention. Cryptorchid dogs -- those in which only one testicle has descended -- should have the retained testicle removed, as many retained testicles become cancerous. Dogs who have retained testicles should not be bred, as cryptorchidism is often hereditary. Some breeds of dogs are more prone to testicular cancer, including German shepherd dogs, Weimaraners, Shetland sheepdogs and boxers, so particular care should be taken with those breeds.