Prostatic Tumors

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Prostatic Tumors

By: Dr. Douglas Brum

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Section: Information In-depth

Prostatic neoplasia is a very aggressive type of cancer. It is quick to metastasize (spread), and has often done so by the time the diagnosis is reached. It commonly metastasizes to the lymph nodes under the lower lumbar area of the back near the pelvis, the bones of the lower lumbar vertebra and pelvis, the liver or the lungs. The disease is equally prevalent in both intact and neutered dogs, but seems to be more aggressive in neutered animals. In either case, the tumor is very serious and has a poor prognosis.

The location and anatomy of the prostate is important in understanding the clinical signs associated with prostatic neoplasia. The prostate is located just behind the urinary bladder and under the colon. The prostate encircles the urethra (tube that carries urine from the bladder through the penis and out of the body) as it exits the bladder.

The prostate is made up of two symmetrical parts, or lobes, located on either side of the urethra. When the prostate is small it sits within the pelvic canal, but as it increases in size, it moves forward into the abdomen. The prostate can usually be palpated through the rectum, by digital examination. Most dogs with prostatic tumors have an asymmetrical enlargement of one of the prostatic lobes, or have palpably firm nodules. The prostate may or may not be painful.

As the tumor grows it may compress the colon causing straining to pass stool or constipation. The tumor can also invade the urethra, causing bloody urine and straining to urinate. If the cancer has spread to the bones of the lower back or pelvis, back pain and pelvic weakness may be noted.

It is very important to note whether a dog is intact or neutered, as the normal size of the prostate gland in an intact dog would be considered abnormal in a neutered dog. The most common cause of prostatic enlargement in the neutered dog is a tumor. In intact dogs there are a variety of likely causes of prostatic enlargement. Diseases that may cause similar clinical signs as prostatic tumors include:

Benign prostatic hyperplasia. BPH is the most common form of prostatomegaly (enlarged prostate) in the intact male dog, with virtually all acquiring the condition as they age. It is caused by an increase in number and size of the prostate cells as the intact dog ages and is exposed to normal hormonal influences. It is a benign condition that usually does not cause any clinical signs. The majority of the time this condition is found incidentally on routine physical examination. The prostate is generally symmetrically enlarged and not painful.

Chronic prostatitis. Prostatitis is a bacterial infection of the prostate gland. The chronic (long term) form may present with the same historical and physical findings as an animal with prostatic cancer. Additionally, it is not uncommon for a dog with prostatic cancer to also have concurrent infection. It may be very difficult to differentiate between the two without a biopsy.

Prostatic abscess. An abscess is a walled off pocket of infection containing white blood cells, bacteria, and cellular debris. Abscesses occasionally form within the prostate gland in cases of chronic prostatic infections. They may get to be quite large and cause compression of both the colon and urethra. Straining to defecate or urinate may be seen, and most animals are feeling ill.

Paraprostatic cyst. Paraprostatic cysts are fluid-filled sacs that are connected to the prostate by a thin stalk. Single or multiple cysts may be seen, and they can get very large. Animal's usually only feel ill if the cysts become large enough to compress other internal organs. They can also cause compression of the colon or urethra.

Squamous metaplasia. Squamous metaplasia is a change in the prostate gland due to elevated blood estrogen levels. The prostate gland generally becomes bilaterally symmetrically enlarged. The main cause of this is an estrogen-producing tumor (Sertoli cell tumor). Long-term oral estrogen supplementation can also cause these changes.

Metastatic disease to the prostate. Cancer from elsewhere in the body can spread to the prostate and cause the clinical signs typically seen.

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