Cancer is not a single disease but a wide variety of them, with differing causes and outcomes. In the first of a two-part series on cancer in animals, we will talk about cancer in general. In the next article in our series, we will go into detail on the more common and important cancers we encounter in animals.
Cancer tends to occur in older pets, although any age pet can get cancer. I diagnosed cancer of the lymph nodes in a 9-month-old dachshund when I first started practicing over 35 years ago.
Older dogs and cats might be lethargic, have a poor appetite, and lose weight. They may also exhibit changes in urinary and bowel habits. Bleeding from any area can also be a sign of cancer. Since these are the symptoms of other diseases of aging pets in addition to just general symptoms of old age, it can be difficult to differentiate them from one another. An exam and diagnostic tests are implemented to make a specific diagnosis.
Some of the more common signs that could indicate cancer include the following:
- Your pet is not as active as it used to be, or its appetite might be diminished.
- There is an unusual odor from the mouth or other body cavity. Odor can mean an infection by itself, or it can mean an infection secondary to cancer. This is especially true with odors from the mouth.
- Your pet urinates blood or strains to urinate. Even though this is usually a sign of an infection or inflammation of the urinary tract, it can occasionally be a sign of a type of bladder cancer called transitional cell carcinoma.
- Your pet limps on one or more legs. Bone cancer tends to occur in the larger breed dogs and is usually diagnosed with a radiograph.
- Your pet has a chronic cough that does not go away or recurs after treatment with antibiotics. This could be a sign of cancer in the lungs.
- The respiratory rate increases, or you see difficulty in breathing. This could be a result of fluid around the lungs, which may be a secondary sign of cancer.
- Pale gums could indicate anemia secondary to cancer of an internal organ.
- There may be unexplained bleeding, especially around the mouth, nose, anus, or reproductive organs.
- Your pet may exhibit chronic vomiting or diarrhea, which is common in cancer of the stomach and intestines.
- Chronic weight loss is also common in cancer.
- There may be enlarged, swollen or painful external lymph nodes. Remember to check these during the home diagnosis I described in an earlier article. During a routine physical exam, one of our doctors or your own vet can teach you how to palpate the easy-to-find peripheral lymph nodes. If you want more specific information, the peripheral lymph nodes are named as follows: submandibular—under the jaw, prescapular—in front of the shoulder, axillary—in the armpit, and popliteal—on the back legs opposite the kneecap. You can find this information and see pictures of how to palpate these lymph nodes on our website. Follow the Learning Center link and scroll down to the In Home Exam.
- Any lump that rapidly enlarges or is bothering your pet can be a sign.
- A distended abdomen could indicate fluid in the abdomen from cancer. This can be difficult to discern in longhaired pets and those that are obese.
This tiny ulceration at the tip of this cat’s nose is typical of the subtle lesion that is possible with squamous cell carcinoma.
During any routine physical exam, we look for any sign of cancer, although these clinical findings might not be exclusive to the disease. We look at the mucous membranes, eyes and face for signs of anemia, swelling or growths. We check the external lymph nodes for pain, enlargement or inflammation.
We palpate the abdomen for signs of fluids, an enlarged internal organ or a mass on one of these organs. We listen to the lungs for changes in lung sounds in addition to the heart rate and rhythm. We also run our hands along the hair coat for growths, swellings or inflamed areas.
One of the first diagnostic tests we perform for the detection of cancer is a comprehensive blood panel. Some cancers, notably those of the bloodstream, might show up when checking the red or white blood cells. A particular type of white blood cell called a lymphocyte could give us an indication of lymphosarcoma, a common malignant pet cancer.
The rest of the blood panel checks the internal organs, electrolytes and thyroid level. Significant deviations from the normal could be a sign of cancer, although cancer can be present in an internal organ and these tests might have normal results. This means that a normal blood panel does not guarantee that your pet does not have cancer; on the other hand, abnormality can be caused by diseases other than cancer.
Radiography (X-ray) is an important tool in the detection of internal cancers that have no external signs. When looking at a chest radiograph, we can sometimes see fluid or tumors in or around the lungs. We can also see a heart that might have a mass. There is a lymph node in the chest called the sternal lymph node that we look at closely for cancer.
Radiography of the abdomen can show abnormal fluid, an enlarged organ, a mass on an organ and even enlarged internal lymph nodes. Bone cancers are commonly diagnosed with radiography because of their specific appearance.
In a pet that already has cancer we can look for spreading, called metastasis, to the lungs, a common location for cancer to localize when it spreads from another organ.
Ultrasound is a very valuable tool in assessing the internal organs for cancer of the abdomen as well as many other problems that mimic cancer. It has almost replaced exploratory surgery in our hospital because it is noninvasive and less expensive than this surgery. We have a special doctor perform our ultrasounds for rapid and accurate diagnosis.
Specialized tests are sometimes needed to confirm a diagnosis. This could include endoscopy, fluoroscopy and CAT scans. MRIs are used to diagnose cancers of the central nervous system, which comprises the brain and spinal cord.
Our web page has a few case studies of pets that have been diagnosed with and treated for cancer. Click on each condition to go to its link: