It is easy for owners to jump to the wrong conclusion and think “cancer” whenever their pets become ill. While the frequency of cancer in pets does seem to be increasing, most ill pets do not have cancer! However, any time a pet has an illness that does not respond well to treatment within four to eight weeks, the possibility of cancer must be considered.

Cancer can mimic signs of other disorders such as kidney disease, inflammatory bowel disease, or urinary tract infections.

Some common physical complaints for which cancer may be suspected, but which are commonly caused by diseases other than cancer, are vomiting, diarrhea, weight loss, coughing, sneezing, lumps under and on the skin, and changes in appetite, thirst, and urination.

Gastrointestinal signs: Vomiting, diarrhea, weight loss

Chronic gastrointestinal signs such as vomiting, diarrhea, and weight loss can occur as a result of cancer of the gastrointestinal tract, or cancer anywhere else. However, the most common cause of weight loss, vomiting, or diarrhea that persists for more than one month is usually inflammatory bowel disease (IBD). IBD is rarely caused by gastrointestinal cancer and most often caused by an infiltration of white blood cells into the pet’s intestines. Very rarely, an infection (usually fungal) of the intestines can cause IBD. early diagnosis and treatment of IBD is very important because chronic inflammation can progress to cancer. Chronic vomiting, weight loss, or diarrhea should be investigated by endoscopic examination (examining the intestinal tract with an endoscope while the pet is anesthetized) and biopsy of the intestines to determine the exact cause. A hormonal disease affecting the adrenal glands called Addison’s disease can also cause chronic gastrointestinal signs, especially intermittent vomiting, and should be considered as a possible cause.

Respiratory signs: Coughing and Sneezing

Acute coughing is usually the result of allergies or an infection, such as the infection that causes kennel cough. Chronic coughing can also result from hear disease, heartworm infection, lung infections (usually fungal if the problem is chronic), and chronic irreversible bronchial disease (which is especially common in small breed older dogs), but rarely lung cancer. Unlike in people, primary lung cancer is rare in dogs. WHen cancer of the lungs occurs, it is usually the result of metastatic disease after a cancer somewhere else in the body spreads to the lungs. Sneezing is usually the result of allergies or a respiratory infection. Cancer should be suspected if the pet has a nasal discharge that is confined to one side of the nasal cavity and if the discharge contains blood. Dogs with longer noses, usually characteristic of large breeds, are more prone to nasal and sinus cancer than other breeds.

Lumps and Bumps

As discussed in the previous chapter, there are many forms of cancer that can appear on an animal’s skin. Fortunately, most lumps and bumps (technically referred to as nodules or tumors) are benign fatty tumors or epidermal cysts. However, these lumps and bumps are sometimes cancerous tumors, including mast cell tumors or connective tissue tumors such as fibrosarcomas. Dogs with multiple lumps on their bodies that appear suddenly may be afflicted with a type of cancer called lymphosarcoma, also referred to as lymphoma. These lumps usually occur in areas where the lymph nodes are located, such as under the jaw, in the armpits, in the groin, and in front of the shoulder blades. Owners should also keep in mind that any lumps and bumps that appear, then decrease in size or even disappear, and finally reappear and enlarge are more likely to be cancer (often lymphoma) than benign lumps or infectious lesions.

Changes in appetite, thirst, and urination

The most common causes of changes in appetite, thirst, and urination are diseases other than cancer that are commonly diagnosed in older dogs. these include diabetes mellitus, kidney disease, liver disease, bladder infections, urinary incontinence, and bladder stones. these diseases are so commonly diagnosed that I believe all dogs, but especially those five years of age and older, should be checked at least twice yearly with simple blood and urine tests, in addition to a thorough physical examination, to ensure early diagnosis and treatment of these conditions; most pets with these conditions can live comfortably by using a holistic approach treatment.

Abnormalities in blood or urine tests

Unlike in people, leukemias and blood cancers are very rare in pets. Most commonly, changes in the red or white blood cell counts occur as a result of anemia (often secondary to any chronic disease), infection, or inflammation somewhere in the body. When the counts for several different cell types(red cells, white cells, and platelets) increase or decrease on the complete blood count, a bone marrow aspirate should be performed to investigate if cancer may be the cause.

While a blood test will not usually tell if a pet has cancer, elevated calcium levels are often seen in pets with cancers such as lymphoma or anal sac cancer (adenocarcinoma). Pets with high calcium levels must be carefully examined for cancer if no other cause of the elevated calcium is apparent from the pet’s medical history and physical examination. One cause of elevated calcium is Vitamin-D rodenticide poison.

Recently, a tumor antigen test (V-BTA) became available that purported to help screen for TCC in its early stages. Unfortunately, blood in the urine causes false positives in this test, and because bloody urine is the chief symptom in TCC, the test is not felt to be useful at this time.

I remind pet owners not to suspect cancer everytime a pet becomes ill. having a pet examined early in the course of any illness will usually allow for a prompt diagnosis and the correct treatment. In the unfortunate event that some type of cancer is in fact responsible for the pet’s illness, early diagnosis ensures quick intervention, which can extend the pet’s life and, in some cases, totally cure the pet of cancer.

Clinical signs that might indicate cancer in dogs
  • Lumps and bumps (especially new ones; those that grow quickly; those that appear, decrease in size or disappear, and then reappear or enlarge; and those that change color or easily bleed)
  • Skin sores and irritated areas
  • Skin sores and irritated areas
  • Red spots on the skin, gums, or mucous membranes
  • Wounds that do not heal
  • weight loss or gain
  • lack of appetite or decreased appetite
  • Abdominal enlargement (potbellied appearance)
  • Weakness or exercise intolerance
  • Excessive panting or heavy breathing
  • Collapse
  • Pale gums or mucous membranes
  • Bad breath
  • Bleeding or chronic discharge from wounds or any body orifice
  • Change in bowel habits (chronic diarrhea, vomiting, or both)
  • Change in urinary habits (blood in the urine or urinary incontinence)

NOTE: While cancer can cause these signs, so can many diseases. (Consult your veterinarian for more information)

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Shawn Messonnier, D.V.M., is a holistic veterinarian and nationally recognized expert on integrative medicine for animals. A graduate of Texas A&M University School of Veterinary Medicine, he has served as Editor-In-Chief of DVM Management Consultant Reports as well as The Practical Veterinarian Series. His holistic medicine columns have appeared in such journals as MSLO’s own, The Dallas Morning News, Veterinary Forum, Alternative Medicine, Animal Wellness, Pet Business Magazine, Dog Fancy, Cat Fancy, and Cats Magazine. Martha Stewart Omnimedia (MSO) has selected Dr. Shawn Messonnier as the pet care expert for her new radio network. The Natural Vet show airs live each Tuesday at 7 PM CST on Martha Stewart Radio Sirius channel 112.

Dr. Shawn is the author of several books, including the award-winning Natural Health Bible for Dogs and Cats, The Allergy Solution for Dogs and The Arthritis Solution for Dogs. He owns the Paws & Claws Animal Hospital in Plano, Texas. You can find out more about Shawn Messonier by logging on to his website: