What is the prostate?
The prostate is a small gland located near the neck (outlet) of the urinary bladder of male dogs. The urethra (the tube that carries urine from the bladder to outside the body) passes through the prostate shortly after leaving the bladder. The prostate produces fluids found in semen.
What is a prostate tumor?
Prostatic tumors develop from the cells responsible for semen fluid production. Prostatic tumors are rare in dogs and extremely rare in cats. The most commonly diagnosed prostatic tumor is prostatic adenocarcinoma.
Benign (non-cancerous) prostatic masses can also develop and are similar to benign prostatic hyperplasia (proliferation of non-cancerous tissues) in older men, though these masses are rare in dogs.
What causes this type of cancer?
The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.
"Very few tumors and cancers have a single known cause."
In the case of prostate cancer. A mutation in a specific gene (BRAF) has been discovered in many dogs with prostate carcinomas. Both neutered and un-neutered (intact) males can develop prostate tumors. Breeds that appear to be at increased risk include the Bouvier des Flandres, Doberman Pinscher, Shetland Sheepdog, Scottish Terrier, Beagle, Miniature Poodle, German Shorthaired Pointer, Airedale Terrier, and Norwegian Elkhound.
Benign growth (prostatic hyperplasia) of the prostate is seen commonly in older dogs that have not been castrated (neutered). It is related to effects over time of the male sex hormone, testosterone, from the testicles.
What are the clinical signs?
Given the location of the prostate, the most common clinical signs include blood in the urine, a change in urination habits, inability to urinate, and excessive drinking. The colon, located just above the prostate, may become compressed, making it difficult to pass bowel movements. Pets may strain to urinate or defecate, and the stools may become flattened or ribbonlike. Other signs may include lethargy, exercise intolerance, reduced appetite, weight loss, and pain (especially along the back or abdomen). The pain may be significant in pets that have evidence of metastasis (spread) to the bones of the lower back and pelvis.
How is this cancer diagnosed?
Your veterinarian may feel an enlarged prostate during a physical examination. With this finding, your veterinarian may recommend certain diagnostics to determine why the prostate is enlarged and if it could be due to a tumor. This may include obtaining a sample of cells from the prostate either by catheterization (insertion of a catheter into the urethra all the way to the prostate) or by performing an ultrasound-guided fine needle aspiration (FNA) of the prostate.
FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the prostate. The cells are placed on a microscope slide. A veterinary pathologist then examines the slide under a microscope. When a diagnosis cannot be made with either of these procedures, a surgical biopsy may need to be considered.
"Urine tests will often show high protein levels, red blood cells and possibly white blood cells and cancerous prostatic cells."
Bloodwork may also be recommended. This may show a high calcium level due to a protein produced by the tumor. Urine tests will often show high protein levels, red blood cells and possibly white blood cells and cancerous prostatic cells.
How does this cancer typically progress?
Prostatic carcinoma is typically a locally aggressive tumor with a high likelihood of metastasis (spread to other areas of the body). One of the main concerns with prostate tumors is the potential of metastasis to bone. Up to 42% of dogs with prostatic carcinoma develop metastasis to the bones, most commonly the pelvis or lumbar vertebrae (bones in the region of the prostate).
Staging (searching for potential spread to other locations in the body) is highly recommended. This may include bloodwork, urinalysis, X-rays of the lungs and/or abdomen, a full abdominal ultrasound and possibly CT or MRI. If any lymph nodes are enlarged or feel abnormal, further sampling may be pursued to determine if spread is present.
Even though prostatic cancers are associated with a high rate of spread, the local disease can become problematic as well. As the tumor grows it may completely compress, or grow into, the urethra, causing significant discomfort and potentially the inability to urinate. In these cases, surgery or surgical stent placement (to allow an opening for urine to flow through) may be discussed as palliative measures to reduce the impact of the disease and improve your pet’s quality of life.
What are the treatments for this type of tumor?
The treatments for prostatic carcinoma are aimed at reducing the tumor’s size and the tendency for metastasis. Surgery may be considered as a palliative measure, though removal of the entire prostate or tumor is not typically successful without damage to the urethra. In pets with significant obstruction of the urethra, a surgical stent may be placed to allow for urination.
Treatments less invasive than surgery, such as radiation therapy, may be pursued. Targeted radiation therapy to the region of the prostate and affected lymph nodes or bone may be possible. Palliative radiation therapy may provide short-term relief for urinary obstruction.
"In pets with significant obstruction of the urethra, a surgical stent may be placed to allow for urination."
The use of nonsteroidal anti-inflammatories (NSAIDs), such as piroxicam or carprofen, have been shown to be beneficial in the treatment of prostate cancer. Chemotherapy used with NSAIDs and radiation has been shown to be more helpful than either treatment alone. Bisphosphonates (medications developed for the prevention of osteoporosis in women) may also be helpful. These drugs are typically recommended with metastasis to the pelvic bone or lumbar vertebrae. They may reduce the active breakdown of the bone and reduce pain.
Is there anything else I should know?
If your pet has been diagnosed with a prostate cancer and becomes unable to pass urine, this is an emergency. Please seek veterinary attention immediately. If your pet is experiencing pain, contact your veterinarian so that your pet’s pain management plan can be modified.
Prognosis for prostate tumors is often poor because they have often metastasized at the time of diagnosis. Although treatments discussed can help alleviate the symptoms for a varying period of time, many relapse within three to six months.