Cancer rates in pets are similar to those in humans, with one in four dogs developing the condition during their lifetime. The rate increases to 50% in pets older than 10 years, and cancer is the leading cause of death in pets overall. The good news is that research into new and innovative treatments that benefit humans and pets is well underway, because cancer is so prevalent across species, and pets with cancer now have more treatment options and higher treatment success rates, and are living longer, healthier lives. Southern Arizona Veterinary Specialty and Emergency Center understands the uncertainty and anxiety surrounding a cancer diagnosis, so in light of November’s National Pet Cancer Awareness Month, we want to help you recognize and understand cancer in pets.

What is cancer in pets?

To explain cancer in pets, it’s helpful to understand the terminology. The words “neoplasia,” “tumor,” and “mass” can be used interchangeably to describe a collection of abnormal cells. Neoplasia can form in almost any body tissue, and can be benign or malignant.

  • Benign tumors — These tumors don’t invade or destroy tissues and don’t spread to other body parts (i.e., metastasize), but they can still cause problems by irritating, compressing, or displacing other tissue.
  • Malignant tumors — Malignant tumors, which can infiltrate tissue and spread throughout the body, are what we typically think of as cancer.

Cancer in pets can range in severity from a small, isolated, slow-growing tumor, to a highly aggressive, quickly growing metastatic tumor. Severity depends on the tumor type, grade, and predicted behavior.

What causes cancer in pets?

Unfortunately, science doesn’t understand exactly why only some pets develop cancer, but research is ongoing. Because we don’t completely understand how cancer starts, prevention can be difficult, but good strategies include feeding your pet a healthy diet, ensuring adequate exercise, and avoiding second-hand smoke.

What does pet cancer look like?

Cancer appearance and signs vary depending on the individual pet, tumor type, and tumor stage. Some tumors are externally visible, while others are internal and more difficult to recognize. Skin and subcutaneous tumors that appear as lumps or bumps on or under skin are common in pets.

When your pet has a lump, you should recognize that many of these tumors, including fatty tumors (i.e., lipomas) and wart-like growths (i.e., adenomas), are benign, but you should consult your veterinarian in case they are cancerous. Skin tumors sometimes have a characteristic appearance that aids in diagnosis, but malignancy can be diagnosed definitively only by a biopsy examined at a lab. This is generally a quick outpatient procedure performed by your primary veterinarian.

Internal cancer types, or metastatic cancer, can cause more mysterious and varied signs. Sometimes cancer comes on slowly and signs worsen over time, while sometimes pets appear healthy until the tumor causes sudden, critical illness. The most common cancers in pets include:

  • Lymphoma, which involves the lymph nodes and bone marrow
  • Osteosarcoma, involving the bones
  • Hemangiosarcoma, which arises from blood cells in major organs
  • Mast cell tumors, which can arise anywhere, especially on the skin 

Cancer can cause problems with the organ system involved, but some tumors also secrete inflammatory substances that affect the whole body. Some common tumor signs include:

  • Unexplained weight loss
  • Increased thirst and urination
  • Clotting problems or sudden bleeding
  • Coughing or difficulty breathing
  • Abdominal distention
  • Weakness, collapse, and pale gums resulting from internal bleeding
  • Firm, painful swelling

If you notice concerning changes in your pet, have your veterinarian check things out right away—early detection is key for successful treatment.

How is pet cancer diagnosed?

Biopsy of the tumor with histopathology at an outside laboratory is the gold standard for cancer diagnosis, and can also provide information about tumor behavior. Chest X-rays and abdominal ultrasound are used to “stage” disease, based on whether or not tumors have spread to these areas. Blood and urine tests can give information about overall health status and monitor for problems during treatment.

How is pet cancer treated?

Treatment for cancer is multifaceted, and focuses on extending life while maintaining life quality. Surgery, chemotherapy, and radiation are common treatments, and immunotherapy can help the pet’s own immune system target tumors. Pets typically handle chemotherapy better than humans, because treatment goals are different in pets, and lower doses are used. Universities and teaching hospitals often conduct research trials with experimental treatments that may help some pets and defray treatment costs. 

Some cancers can be cured, others may go into remission for months or years, and others won’t respond well to treatment. Aggressive metastatic cancers are often treated palliatively (i.e., focusing on pain control and quality of life rather than a cure). A veterinary oncologist can provide more information about your pet’s cancer type and help you decide which, if any, treatment plan is best for your pet. 

Cancer is a common pet diagnosis, but treatments have come a long way in recent years. If your pet is diagnosed with cancer, contact the oncology team at Southern Arizona Veterinary Specialty and Emergency Center to learn more about our innovative treatment options.