Overview
As male dogs age, they are increasingly prone to developing disorders of the prostate gland. Unfortunately, prostatic cancer (neoplasia) is one of them. Prostate tumors are space-occupying masses that cause the prostate to become enlarged. Most cases are diagnosed when owners bring their dog to a veterinarian because it seems to be having difficulty urinating and/or defecating. Dogs (especially older dogs) displaying these signs should have a simple rectal examination during which the veterinarian will assess the size and texture of the prostate gland. Depending upon the results of this examination, further tests may be appropriate.
Diagnosing Prostate Cancer in Dogs
Veterinarians usually perform abdominal and rectal palpation during a routine physical examination of older male dogs, particularly when owners mention signs of urinary difficulty. In cases of prostatic neoplasia, the veterinarian will feel a large, asymmetrical, irregular and painful prostate gland. They also may find a palpable mass in the abdomen.
The next diagnostic step is to perform an ultrasound of the prostate gland. This is the preferred method for assessing the prostate, as it can help the veterinarian distinguish between prostatic cysts, abscesses and tumors. Abdominal ultrasound can disclose evidence of metastases consistent with cancer, such as bony changes. A fine needle aspirate of cells from the prostate can be done with ultrasound guidance to help distinguish between benign prostatic hypertrophy (BPH), prostatitis and cancer. However, one potential negative consequence of this procedure is that it can cause seeding of the surrounding tissues with bacteria if indeed the prostate has a bacterial infection rather than neoplasia.
Biopsy of the prostate, with subsequent microscopic (histopathologic) evaluation of the sampled tissue, is the only definitive way to diagnose prostatic cancer. A “biopsy” involves the removal and examination of tissue from a living body and normally involves taking an actual piece of tissue, not just cells or fluid aspirated through a needle and syringe. Biopsy of the prostate will enable the veterinarian not only to diagnose the existence (or absence) of cancer, but also to identify what type of cancer (if any) is involved.
Blood, urine and semen sampling and assessment may also be used when prostatic disease is suspected. These will not be diagnostic but can help rule in or out certain other causes of the dog’s clinical signs. Computed tomography (a CT scan) can be used to help plan the best course of surgical or other therapy.
Most prostatic tumors are locally advanced and have metastasized by the time they are diagnosed (70-80% in some reports). Ultimately, almost all will metastasize if left untreated.