Prostatic Tumors in Dogs

Overview of Prostatic Tumors in Dogs

Prostatic tumors or prostatic neoplasia is cancer of the prostate gland. All tumors of the prostate gland should be considered malignant, as there has not been a report of a benign prostatic tumor. The most common tumor of the prostate is prostatic adenocarcinoma. Transitional cell carcinoma is also seen.

The incidence of prostatic disease is fairly low in dogs, and very rare in cats. The cause of prostatic neoplasia is unknown.

Prostatic cancer may affect any breed of dog, but is usually seen in older (average age is about 9-10 years old), medium to large breed dogs. It only occurs in male animals. Castrated male dogs and intact (non-neutered) male dogs are equally as likely to get prostatic cancer.

What to Watch For

Sign of prostatic tumors in dogs may include:

• Straining to urinate or defecate
• Blood in the urine
• Discharge from the penis
• Constipation
• Abdominal discomfort
• Stiff gait
• Weakness in the rear limbs
• Weight loss
• Fever
• Anorexia
• Lethargy

Diagnosis of Prostatic Tumors in Dogs

• History and physical exam including digital rectal exam
• Complete blood count
• Biochemical profile
• Urinalysis with culture and sensitivity
• Cytologic (microscopic) evaluation of seminal or prostatic fluid
• Prostatic massage and wash for cytology, and culture and sensitivity
• Abdominal radiographs (X-rays)
• Abdominal ultrasound with or without prostatic aspiration
• Distention retrograde urethrocystography
• Thoracic (chest) radiographs

Treatment of Prostatic Tumors in Dogs

• Radiation therapy
• Chemotherapy
• Prostatectomy (the surgical removal of the prostate)

Home Care and Prevention

Since most prostatic tumors have a poor response to treatment and a short survival time, the most important part of home care is keeping your pet comfortable. If your pet is painful, analgesics (pain medications) may be used. Both nonsteroidal anti-inflammatory (aspirin-like) drugs and narcotics may be used.

Stool softeners may be used if there is significant straining to defecate or constipation. If your dog is undergoing chemotherapy, periodic blood tests and recheck evaluations may be required.

There is no prevention for prostatic tumors. Neutering a dog at a young age has not been shown to decrease the incidence of prostatic tumors.

In-depth Information on Prostatic Tumors in Dogs

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.

In-depth Information on Diagnosis

• A complete history and physical examination is the first step of obtaining an accurate diagnosis in dogs A rectal exam to palpate the prostate is part of this complete exam. It is also very important to note if the dog is neutered or intact, as this affects the diagnostic plan.
• The CBC is a useful test to run in cases of suspected prostatic neoplasia since it evaluates the red and white blood cells. Elevations in total white count can be seen in inflammatory conditions associated with prostatic neoplasia, but usually the count is normal. Anemia, assessed by a low red blood cell count, is occasionally seen in animals with neoplastic disease.
• The biochemical profile evaluates the metabolic status of a variety of organ systems. Since prostatic tumors are a more common occurrence on older animals, it is also a useful screening test to rule out other problems and or associated disease. Liver values may be elevated with the spread of prostate cancer to the liver. The serum alkaline phosphatase enzyme is an enzyme found in the liver as well as bone. It is elevated in about 50 percent of dogs with prostatic cancer. If the tumor has invaded the urethra, a partial or complete urinary obstruction may occur, and cause an elevation in kidney values.
• A urinalysis will detect inflammatory changes or blood in the urine. It would be uncommon to detect tumor cells in a urine sample, but a urinalysis is still a useful test. The urinalysis can detect concurrent urinary tract infections and suggest other causes of the observed symptoms. A culture and sensitivity is done on the sample to determine if any bacterial growth is present.
• Cytologic (microscopic) evaluation of seminal fluid obtained via an ejaculate is a useful diagnostic tool when testing for prostatic cancer. Since the prostatic fluid is concentrated in the last part (third fraction) of the ejaculate, this is the part that is analyzed. Tumor cells are most often found in this fraction. This test is not often done, since obtaining a sample may be difficult, especially with an ill, painful or uncooperative patient.
• A prostatic massage and wash is another method for evaluating prostatic fluid. There are several techniques for obtaining this sample. Briefly, a urinary catheter is passed to the level of the prostatic urethra and the prostate is digitally massaged through the rectum. A sample is obtained by flushing fluid into the area. The fluid is then aspirated back through the catheter. This sample is submitted for cytology and culture. Inflammatory or tumor cells may also be recovered.
• Abdominal radiographs are very useful in evaluating the abdominal organs and the extent of prostatic enlargement. The general size and shape of the prostate is noted, and the lymph nodes that drain the prostate (sub-lumbar lymph nodes) are evaluated for enlargement that may be seen with metastatic spread. Significant prostatic enlargement may cause the colon to be pushed upward and compressed, while the bladder may be pushed further into the abdomen. Abnormal calcification of the prostate is easily visualized radiographically and sometimes correlates with a neoplastic process (infection can also cause these changes). The bones, especially the lumbar vertebral bodies or the pelvis may show lytic areas (areas of bone erosion) indicating metastatic spread of prostatic neoplasia.
• An abdominal ultrasound can evaluate the texture and consistency of the prostate, as well as size and shape. Ultrasound alone cannot diagnose prostatic neoplasia. Abdominal lymph nodes are observed for enlargement. In order to obtain a more specific diagnosis, an area that is identified as abnormal may be aspirated or biopsied using the ultrasound for guidance. Fine needle aspiration is useful in collecting fluid from cysts or obtaining small cell samples from the prostatic tissue for cytologic evaluation (microscopic evaluation of the cells obtained). A biopsy provides a better sample as a core of tissue is obtained for histopathology (microscopic examination of tissue). Biopsy usually provides more accurate information about the pathology of the prostate, since a larger amount of tissue can be evaluated.
• Distention retrograde urethrocystography is a technique where dye and air are injected through the urethra and into the bladder. This technique allows the urethral lining to be visualized, and better defines the bladder, prostate and any associated mass lesions that may be present. It may be a useful diagnostic test to use if a compressive or invasive urethral lesion is suspected.
• X-rays of the chest are indicated any time prostatic neoplasia is suspected. Thoracic radiographs may show evidence of tumor spread to the lungs. Unfortunately if prostatic cancer is present, and even if the chest films are clear of visible tumors, there is still a reasonable chance that the cancer has spread.

In-depth Information on Therapy

Unfortunately the prognosis of any dog with prostate cancer is quite poor, regardless of the treatment attempted. Without treatment, most dogs die within a few months of diagnosis. Treatment may provide some animals with increased comfort, decreased clinical signs and possibly a slightly increased life expectancy. Thus, the main goal of therapy is to provide more comfort, less pain and more quality for the remainder of the animal’s life.

Types of prostatic neoplasia are treated differently depending on the specific tumor. Adenocarcinoma, the most common form, is also the least responsive to treatment. Transitional cell carcinoma may be prostatic in origin, or may have started in the urethra or bladder initially. Often it is difficult to differentiate where the tumor originated from, but the treatment is the same. The limited treatment options for both tumor types include:

• Radiation therapy. If there is no evidence that the tumor has spread, adenocarcinoma may be treated with radiation therapy. Once again the goal of this therapy is not to cure the disease, but to help improve the clinical signs and provide increased comfort. This type of radiation therapy is called palliation. With the treatment, the tumor size may shrink, and with this may come increased quality of life. Radiation therapy may also be combined with chemotherapy. Radiation therapy is usually available at referral centers.
• Chemotherapy. Chemotherapy is treatment with drugs designed to decrease the tumor size or inflammation associated with the tumor. With transitional cell carcinoma, piroxicam (Feldene®) is the treatment of choice. Piroxicam is a non-steroidal anti-inflammatory medication that is generally well tolerated. Animals with adenocarcinoma do not respond well to chemotherapy alone.
• Prostatectomy. The surgical removal of the tumor and the prostate is a very aggressive procedure that is generally not recommended. It is a very difficult surgery to perform and usually the tumor has already spread. Increased postoperative survival time is questionable and complications (urinary incontinence) are common.

Follow-up Care for Dogs with Prostatic Tumors

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your dog does not improve rapidly.

• Administer all medications as directed. Alert your veterinarian if you are experiencing problems treating your dog.
• If treatment is attempted, the prostate size should be periodically re-evaluated by your veterinarian. Urine should be checked for any secondary infection with cultures and sensitivities.
• Animals on piroxicam are prone to developing gastrointestinal problems (vomiting and or diarrhea). Notify your veterinarian if this occurs. Some veterinarians will use the gastrointestinal protectant, misoprostol (Cytotec®), to decrease the likelihood of these effects.

Follow-up Care for Dogs with Prostatic Tumors

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your dog does not improve rapidly.

• Administer all medications as directed. Alert your veterinarian if you are experiencing problems treating your dog.
• If treatment is attempted, the prostate size should be periodically re-evaluated by your veterinarian. Urine should be checked for any secondary infection with cultures and sensitivities.
• Animals on piroxicam are prone to developing gastrointestinal problems (vomiting and or diarrhea). Notify your veterinarian if this occurs. Some veterinarians will use the gastrointestinal protectant, misoprostol (Cytotec®), to decrease the likelihood of these effects.