These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout "What is Cancer". Your veterinarian may suggest certain tests to help confirm or eliminate diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However, information and understanding about tumors and their treatment in animals is improving all the time.
We understand that this can be a very worrying time. If you have any questions please do not hesitate to ask us.
What is this tumor?
The prostate gland stores sperm from the testicles and produces fluid that contains essential nutrients for the sperm. Cancers of the prostate are rare but usually involve the cells that make the fluid. Although true cancer is rare, non-cancerous overgrowth (hyperplasia) of the gland is common. Both the non-cancerous and cancerous growths have similar clinical signs. These growths usually cause localized pain, and put physical pressure on the surrounding tissues such as the rectum, interfering with the passage of bowel movements. Occasionally there is urinary infection or difficulty with urination.
"Although true cancer is rare, non-cancerous overgrowth (hyperplasia) of the gland is common."
The true cancers frequently spread (metastasize) to the lymph nodes ("glands") and bones so there may be difficulty in walking.
What do we know about the cause?
The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often the culmination of a series of circumstances that come together for the unfortunate individual.
"Hormonal imbalance is important in the first stage of overgrowth (hyperplasia)."
Hormonal imbalance is important in the first stage of overgrowth (hyperplasia). Either an excess of female hormone (estrogen), from certain types of testicular cancer, or an excess of male hormone (testosterone) can cause hyperplasia. Within the prostate, testosterone is converted to dihydrotestosterone, which is then absorbed by the cell nuclei to activate genes required for cell growth. Hyperplasia of the gland occurs in all non-castrated male dogs as they age.
Why has my pet developed this cancer?
Why a few dogs will develop prostate cancer is uncertain. All intact male dogs have some degree of enlargement of the prostate gland as they age. When corrected for age, there is usually a consistent relationship between the size of the gland and body weight. The exception is the Scottish terriers, which has a prostate on average four times the relative weight of that of other breeds. However, this breed does not have a higher incidence of prostatic cancer than other dogs.
Is this a common tumor?
Hyperplasia is a universal condition in older, non-castrated male dogs and causes clinical problems in some. Cancer of the prostate is rare.
How will this cancer affect my pet?
Enlargement of the prostate gland may be evident at 4-5 years of age and the incidence increases with age. Both the non-cancerous and cancerous growths cause similar signs, mostly due to physical effects. The enlarged prostate gland commonly presses on the rectum, interfering with passing feces. Less commonly, it may interfere with passing urine. There enlargement may be painful, and occasionally, there will be a secondary infection in the urine.
Malignant cancers may spread through the body by invading the lymph transport system and then seeding in bones, brain and other organs. Difficulty walking and weight loss due to loss of body fat and muscle may be seen with malignant prostatic cancer.
Some of the malignant tumors induce signs that are not readily explained by the spread of the tumor. This "paraneoplastic syndrome" is due to abnormal hormone production by the cancer. With prostatic cancer, there may be increased blood calcium levels and deposits of excess bone on some limbs.
How is this cancer diagnosed?
"A digital rectal examination will usually allow your veterinarian to feel the enlargement of the prostate."
Your veterinarian may suspect prostatic cancer in an intact male dog, based on the specific clinical signs of pain, difficulty passing feces, infection or blood in the urine and difficulty passing urine) A digital rectal examination will usually allow your veterinarian to feel the enlargement of the prostate. X-rays may be useful in detecting the enlarged gland or the spread from a malignant cancer. In order to identify why the gland is enlarged (which hormone is likely to be implicated, whether there is infection or whether a malignant tumor is present), it is necessary to obtain a sample of the tumor cells. Most often, this sample is obtained by prostatic massage and urinary catheterization, which is less invasive than surgery. Cytology, the microscopic examination of these cell samples, can then identify the most probable cause of the swelling. If a tissue biopsy is obtained surgically, histopathology, the microscopic examination of specially prepared and stained tissue sections, may be performed at a specialized laboratory where a veterinary pathologist will examine the prepared slides. Following the examination, the pathologist will report the diagnosis and prognosis to your veterinarian. Malignancy is often shown by the tumor name ending in "carcinoma". This and the stage (how large it is and extent of spread) indicate how the cancer is likely to behave.
What types of treatment are available?
"The best treatment for an enlarged prostate due to hyperplasia is castration."
The best treatment for an enlarged prostate due to hyperplasia is castration. This removes the hormonal stimuli and the prostate will reduce in size except in the rare cases where the hormones are due to cancer of another gland such as the adrenal. There are also drug treatments that act by blocking the formation of hormones or hormonal actions.
The malignant tumors are not responsive to castration, hormonal treatments or common chemotherapy agents. Surgery and radiotherapy are very difficult but surgical removal of the affected gland early in the disease combined with intra-operative irradiation may be successful in some cases.
Can this cancer disappear without treatment?
Cancer rarely disappears without treatment but as development is a multi-step process, most of the overgrowth of this gland stops before it becomes cancerous. The body's immune system is not effective in causing this type of tumor to regress. Rarely, loss of blood supply to a cancer will make it die but this is unlikely to be total.
How can I nurse my pet?
Ensuring your pet is able to pass feces and urine frequently is an important part of the management of prostatic enlargement. Your pet may require a special diet, and you should try to encourage your pet to drink more (to keep the feces soft). After catheterization, ensure he is able to urinate freely.
After surgery, you will need to keep the incision site clean and dry, and prevent your from interfering with it. Report any loss of sutures or significant swelling or bleeding to your veterinarian. You will be asked to ensure that your pet can pass urine and feces, and you may need to give treatment to facilitate this. If you require additional advice on post-surgical care, please ask.
How will I know how this cancer will behave?
"Cytology results and response to castration will be a good indication that your dog does not have malignant cancer."
Cytology results and response to castration will be a good indication that your dog does not have malignant cancer. If the cytology and/or histopathology indicated the presence of prostatic cancer, surgical removal will usually only give remission and the cancer will recur or spread.
Are there any risks to my family or other pets?
No, these are not infectious problems and are not transmitted from pet to pet or from pets to people.