Prostate Cancer in Dogs

Prostate cancer is a disease of elderly dogs, affecting dogs between 8 and 10 years of age. It’s not a common disease; studies suggest that the incidence of this type of cancer is only 0.6%. Although it is rare, when it does occur the prognosis is poor.

What is the Prostate Gland?

The Prostate gland is just beneath the rectum of male dogs, and it surrounds the junction of the urethra and bladder. It produces prostatic fluid which makes up as much as 95% of ejaculated liquid. Thus it plays an important role in successful dog breeding.

The size of the gland varies between dogs, depending on age and size, but it’s usually around 1-2 inches in diameter.

Unlike some other diseases of the gland, prostate cancer isn’t influenced at all by testosterone so it can occur in both neutered and entire dogs.

Symptoms of Prostate Cancer

When the prostate gland becomes cancerous, the whole gland is usually affected. It becomes enlarged and presses on surrounding organs.

Because of its position just underneath the rectum, a swollen gland will interfere with defecation. You’ll notice your dog straining to pass stools. It may also compress the neck of his bladder and make it difficult for him to urinate.

He may also have blood or pus in his urine, and show symptoms of back or hind limb pain and weakness.

How to Diagnose Prostate Cancer

Because there are other conditions that can cause swelling of the prostate gland, such as benign prostatic hypertrophy or prostatic cysts, your vet won’t be able to rely on symptoms alone to make a diagnosis of cancer.

A physical examination is likely to reveal a firm round mass towards the back of your dog’s abdomen. This is followed by a rectal exam to feel the size and surface of the gland. A cancerous prostate is firm and swollen, with an irregular surface. These findings in an elderly dog, in conjunction with the typical symptoms of prostate disease, will make your vet very suspicious of cancer.

There are other diagnostic tests that can confirm or rule out prostate cancer. The first is ultrasound. This is a useful way of differentiating cancer from cysts or abscesses in the gland.

The second is a fine needle aspirate biopsy. This is done by passing a fine needle into the gland, using an ultrasound to guide it, and collecting some cells. These cells are then examined under a microscope by a pathologist. There are advantages and disadvantages to this procedure. While it can help your vet to reach a diagnosis, it may also lead to the spread of bacteria or cancer cells into tissues surrounding the gland.

The best way to confirm a suspicion of prostate cancer is a biopsy, which will allow an actual piece of the gland to be looked at by the pathologist.
In people with prostate cancer, the prostate specific antigen levels in the blood can be used to help diagnose the disease. The prostate gland of dogs produces an enzyme that can also be measured, but it doesn’t help with diagnosing cancer. It is a much better indicator of benign diseases such as prostatic hypertrophy. This means that there is no specific blood test for prostate cancer in dogs.

Treatment and Prognosis of Prostate Cancer

Prostate cancer in dogs has a very poor prognosis. In as many as 80% of affected dogs, the disease has already spread by the time it is diagnosed. It spreads readily to the bladder, lymph nodes, lungs, and bones. The average survival time after diagnosis is usually only a matter of months. Many dog owners choose not to treat the disease and instead provide palliative care. The aim of this is to give their dog a good quality of life with no pain for as long as possible.

Treatment options include:

• Removal of the cancerous prostate gland. This often results in urinary incontinence. Sometimes just a part of the prostate can be removed, to ease some of the symptoms.
• Radiation treatment. Radiation has been used with surgery to treat prostate cancer but studies have shown that it doesn’t extend survival time.
• Non-steroidal anti-inflammatory drugs such as meloxicam have been used to try and slow tumor progression but this too wasn’t as effective as researchers were hoping.
• Photodynamic Therapy. This involves using a photosensitizing drug, light and oxygen to release toxic oxygen radicals. Combined with partial removal of the prostate gland, it has resulted in longer survival times and better quality of life.

There is no chemotherapy protocol that has been effective in treating prostate cancer in dogs.

Conclusion

Prostate cancer is a nasty disease. Its symptoms will make your dog miserable, and the outcome for him isn’t good. Fortunately it is rare. If your much loved canine family member is showing symptoms of prostate disease, have him checked by your vet as soon as possible. An early diagnosis gives him the best chance of having a good quality of life for as long as possible.