How Canine Prostate Cancer is Diagnosed
As male dogs age, they are increasingly prone to developing disorders of the prostate gland. Unfortunately, prostate cancer is one of them. Prostate tumors are space-occupying masses that cause the prostate gland to become enlarged, and they almost always spread to distant locations before they are diagnosed. Most cases are diagnosed when an owner consults with a veterinarian because his dog seems to be having difficulty urinating and/or defecating.
Veterinarians usually perform abdominal and rectal palpation during a routine physical examination, particularly if their patient is an older male dog whose owner mentions signs of urinary difficulty. During the rectal examination, the veterinarian will palpate (feel) the prostate gland to assess its size, texture and contours. In cases of prostate cancer, the veterinarian usually will feel a large, asymmetrical, irregular and painful prostate gland. She also may find a palpable mass in the abdomen. Depending upon the results of the initial history and physical examination, further diagnostic tests may be appropriate.
The initial data base usually includes a complete blood count, serum chemistry profile, urinalysis and urine culture, as the symptoms of prostate cancer can mimic those of a urinary tract infection or kidney disease. Another common test is an ultrasound of the prostate gland. This is the preferred method for assessing the general health of the prostate, as it can help the veterinarian identify and distinguish between prostatic cysts, abscesses and tumors. A fine needle aspirate of cells from the prostate gland can be done with ultrasound guidance, which also can help distinguish between benign prostatic hypertrophy (BPH), prostatitis, abscesses and cancer. However, taking a direct sample of prostate tissue can cause seeding of surrounding tissues with bacteria, if the source of the dog’s discomfort is a bacterial infection or abscess. It also can cause seeding of cancer cells, although the need to determine whether a dog has prostate cancer usually outweighs the risk of tumor seeding.
Thoracic (chest) and abdominal radiographs (X-rays), as well as abdominal ultrasound, can be useful to look for signs of metastasis. Regional lymph nodes can be sampled by fine needle aspiration, or removed entirely, and examined microscopically for the same purpose.
Biopsy of the prostate, with subsequent microscopic (histopathologic) evaluation of the tissue samples, is the only definitive way to diagnose prostate cancer. A biopsy involves removing and examining tissue from a living body. It differs from a fine needle aspirate in that it involves taking actual pieces of tissue, not just cells or fluid, as the samples. Biopsy of the prostate will enable the veterinary pathologist not only to diagnose the existence (or absence) of cancer, but also to identify what type of cancer, if any, is involved.
Semen sampling and assessment may also be used when prostatic disease is suspected. This will not be diagnostic of cancer but can help to rule in or out certain other causes of the dog’s clinical symptoms. Computed tomography (a CT or CAT scan) can be used to help plan the best course of surgical treatment or other therapy.
Most prostate tumors are locally advanced and have metastasized by the time they are diagnosed (more than 80% in some reports). Ultimately, almost all will metastasize if left untreated.