Prostate Cancer (Adenocarcinoma) in Dogs

The prostate gland in male dogs is located between the bladder and the rectum, with the urethra, the tube that transports urine from the bladder out of the body, passing through it. This gland responds to testosterone as well as other hormones, and it is important in semen production. Many dogs have some type of prostate enlargement as they age, which may turn out to be a precancerous condition, especially in castrated dogs. Most prostate cancers arise from the glandular ductal tissue and are found to be adenocarcinomas. This a very fast growing malignant type of cancer that is quick to metastasize and spread to other areas of the body, especially the nearby lymph nodes, the pelvis, and vertebrae in the lower back. Metastasis to the lungs usually takes place in the later stages of the disease. A transitional cell carcinoma (TCC) is another type of tumor that can develop on the part of the urethra that passes through the prostate. TCC is much slower growing and less likely to metastasize than adenocarcinoma, but unfortunately it can sometimes be difficult to tell the two apart. Prostate cancer has similar symptoms to other types of prostate disease. Tumors enlarge the prostate gland so that it presses on the urethra and makes urination difficult. Some dogs have blood in their urine. Depending on the size and placement of the tumor, it may put pressure on the rectum and cause problems with defecation as well. Other symptoms can include abnormal posture or walk, pain, and general signs of illness. Treatment for prostate cancer can be difficult since surgery in this area is not always possible.

Prostate cancer is a common problem in older male dogs. Most tumors of the prostate are a malignant type of glandular cancer, called adenocarcinoma. Adenocarcinoma is an aggressive cancer that spreads quickly to other parts of the body.

Seek veterinary treatment immediately if you notice any of the following symptoms.

• Difficulty urinating (stranguria)
• Blood in the urine (hematuria)
• Frequent attempts to urinate
• Difficulty defecating
• Lameness in the hind legs
• Abnormal posture (especially while urinating)
• Abnormal gait with short steps
• Pain
• General weakness
• Weight loss
• Fever

Types

These are the most common types of prostate disease in older dogs.

Benign prostatic hypertrophy (BPH)

• Prostate enlargement that is usually triggered by the long-term effect of testosterone; often a precancerous condition especially in castrated dogs

Adenocarcinoma

• A carcinoma arising from the glandular tissue in the prostate; the most common and most malignant type of prostate cancer

Transitional cell carcinoma (TCC)

• A carcinoma arising from the lining to the urethra in the prostate; this is as slower growing and less malignant type of cancer than adenocarcinoma. It may also be present in the bladder.

The exact cause for any type of cancer can be difficult to trace. The risk for prostate cancer increases with age, and most cases are diagnosed in male dogs over eight years old. Veterinarians disagree somewhat about the role of hormones in prostate cancer, but instances are generally believed to be higher in ucastrated animals.

The symptoms of prostate cancer are often non-specific since they can also be associated with other types of prostate disease, as well as kidney or bladder infection. The veterinarian will complete a thorough physical examination, including rectal palpation, to check for signs of an enlarged or abnormally shaped prostate. Small samples of cancerous cells can often be found with urinalysis, so this is often an effective way of confirming suspected prostate cancer. Bloodwork will also be taken to evaluate for infection or systemic illness, which might suggest another cause for your dog’s symptoms.

Ultrasound will help to evaluate the size and shape of the prostate more accurately, as well as check for local metastasis. An ultrasound guided biopsy may be necessary to obtain a larger sample of the tumor and diagnose the type of cancer and the degree of malignancy, if possible. Further X-rays of the bones or lungs may be ordered to check for metastasis to these areas. About 80% of dogs with prostatic adenocarcinoma have some type of metastasis present upon diagnosis.

Tumors of the prostate gland are rarely treatable with surgery. In dogs, removal of the entire prostate gland usually results in incontinence, and, with the common rate of metastasis, this isn’t an effective way of eliminating the cancer. NSAID’S are often given to prolong survival time, especially drugs like piroxicam or carprofen. This treatment increases the median survival time for dogs with prostate cancer to about 7 months. Chemotherapy and radiation therapy combined with NSAID’s can provide a somewhat more effective treatment. Chemotherapy injections given approximately every three weeks increases median survival time to about 10 or 11 months. Chemotherapy appointments will last for at least an hour and a half and dogs often have gastrointestinal side effects.

Radiation therapy combined with chemotherapy and NSAID’s is the most effective treatment, with a survival time of about 20 months. Intensity-modulated image-guided radiation treatment (IM/IGRT) is more effective than external beam radiation for this type of tumor. There is still some chance that dogs will become incontinent with this treatment, since radiation can result in fibrous tissue build-up in the bladder. Other side effects include gastrointestinal or genitourinary toxicosis. Dogs often need to be hospitalized during radiation treatment so that veterinary nurses can monitor the side effects.

The chances of recovery can vary quite a bit based on the aggressiveness of the tumor and the time of diagnosis. If the cancer is found early, before metastasis is present, chemotherapy and radiation treatment may be effective. If significant metastasis has already taken place, the veterinarian may recommend against this type of treatment, and will manage your dog’s illness symptomatically as long as possible. The best way to deal with prostate cancer is to monitor your dog closely, especially as he ages. Diagnosing prostate disease in the precancerous stages can help give your dog the highest chance of effective treatment.