Cancer in pets

A cancer diagnosis in a beloved pet can be heartbreaking—but it’s not always the end of the story. Pets today have a better chance of being successfully treated for cancer than ever before, thanks to major advances in early recognition, diagnosis, and treatment. Understanding what cancer is—and what signs to look for—can help you act quickly and make informed choices.

What is cancer?

Understanding cancer starts with an understanding of neoplasia. Neoplasia is the uncontrolled, abnormal growth of cells or tissues in the body. This growth often forms a mass called a neoplasm or tumor. 

Neoplasia can be either benign or malignant. Benign neoplasms aren’t cancerous and usually don’t threaten a pet’s life unless they press on vital structures like blood vessels or nervous tissue. They tend to grow slowly, displacing but not invading the surrounding body tissues. And they don’t spread throughout the body. For pets, common examples are lipomas (fatty tumors) and sebaceous adenomas (a type of skin tumor).

Malignant neoplasms, on the other hand, are cancerous and potentially life-threatening. They can be unpredictable and grow at various rates, sometimes rapidly. They invade the tissues around them and spread—or metastasize—to other parts of the body. A few examples are lymphoma (a cancer involving uncontrolled growth of certain white blood cells), osteosarcoma (a type of bone cancer), and squamous cell carcinoma (a type of skin cancer).  

The word cancer is often confused with neoplasia, but only malignant neoplasms are truly cancers. 

How common is cancer in pets? 

Approximately 1 in 4 dogs will develop cancer at some point during their life, and this risk increases to 1 in 2 for dogs 10 years or older. Although less common in cats, cancer is a significant health concern for them, too, as well as for several other pet species, particularly as they grow older.

What are the signs of cancer in pets?

Cancer can be challenging to diagnose, especially in the early stages. There are several reasons for this: Many pets are good at hiding signs of illness; the signs they show can be subtle or mimic other diseases; and sometimes there simply are no signs until the cancer has reached an advanced stage. The signs of cancer also depend on the type of cancer, where it’s located, how far it has spread, and other factors.

These are some general warning signs to look out for:

• Loss of appetite and/or unexplained weight loss
• Abdominal swelling or bloating
• Difficulty eating, swallowing, or breathing
• Lumps or bumps that grow or change color or texture over time
• Persistent sores or wounds that won’t heal
• Bleeding from the mouth, nose, or other body openings
• Persistent diarrhea or vomiting
• Unexplained swelling, heat, pain, or lameness
• Behavior changes like hiding or being less interested in things the pet used to enjoy

If you notice any of these signs or think something is wrong with your pet, immediately contact your veterinarian. Several of these signs are also seen with noncancerous diseases, but they still need your veterinarian’s attention to determine the cause. 

The earlier cancer is caught, the earlier your pet can receive treatment, and the better their chance of a good outcome.

How is cancer diagnosed? 

Your veterinarian may suspect cancer based on clues in your pet’s medical history and physical exam findings. Additional tests like X-rays, ultrasound exams, and blood and/or urine tests may be needed to support the diagnosis. 

For most tumors, it’s possible to get basic information about the tumor type by withdrawing some cells from the affected area to examine under a microscope (known as cytology). The results also may confirm a diagnosis for certain types of cancer. For many tumors, a biopsy (collecting a tissue sample from the tumor to examine under a microscope) often is necessary to confirm the diagnosis and help determine if the tumor is benign or malignant. Additional cytology or biopsies of other tissues (like lymph nodes) may be necessary to determine whether and how far the cancer has spread. 

Advanced imaging such as computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) scans can help identify the tumor’s location and possible treatment options. Other tools and techniques can be used to enhance detection of cancerous tissues or cells and identify genetic mutations associated with cancer.

Oncology is the branch of medicine that focuses on the diagnosis and treatment of cancer. Veterinary oncologists are veterinarians who have received advanced training and certification in oncology by a certifying body like the American College of Veterinary Internal Medicine. These specialists work together with veterinarians and pet owners to provide the best possible, most compassionate care for pets with cancer. 

Is cancer preventable? 

Unfortunately, the cause of most cancers is unknown and many different factors may be involved, which makes prevention difficult. One thing we do know is that spaying eliminates the risk of ovarian cancer in female dogs and cats and reduces their risk of mammary cancer, especially when performed before the first heat cycle. For males, neutering eliminates the risk of testicular cancer. 

On the other hand, spaying and neutering may increase the risk of certain other types of cancers. Genetics also can play a role, increasing the risk of some cancers in certain breeds or breeding lines of pets. 

Your veterinarian can answer any questions you have about your pet’s risk of cancer and discuss with you the benefits, risks, and optimal timing of spaying or neutering your pet. 

How is cancer treated? 

Each cancer and cancer patient are different. The good news is that advances in cancer care are allowing treatment to be more precise and tailored to the patient’s specific needs. This may include one or a combination of treatment approaches, such as surgery, chemotherapy, radiation therapy, cryotherapy (killing cancer cells by freezing the tumor), hyperthermia (killing cancer cells by heating the tumor), or immunotherapy (stimulating the pet’s immune system to fight the cancer). Palliative care, which focuses on maintaining a pet’s comfort and quality of life rather than fighting the cancer, also may be an option.

Although for some pet owners the notion of chemotherapy may seem undesirable, pets often tolerate chemotherapy better than people do, with fewer and milder side effects. In considering treatment options, be assured that your veterinarian will prioritize your pet’s comfort, wellbeing, and overall health. Pain management is an important aspect of treatment. Dietary changes or other therapies also may be recommended to help your pet better respond. 

Once you have a diagnosis, your veterinarian can help you determine the best treatment option(s) for you and your pet, and will explain the risks and side effects associated with each. In some instances, your veterinarian may refer you to a board-certified veterinary oncologist or specialty clinic. 

What is the treatment success rate? 

Whether your pet will respond to treatment depends on the type and extent of the cancer, as well as the availability and effectiveness of therapy. Your pet’s age and health status also come into play, as some health conditions can limit treatment options. 

When it comes to the cancer itself, two things can affect treatment success:

• Stage: How large the tumor is and how far it’s spread to other areas of the body
• Type: What the cancer is and how it behaves in terms of aggressiveness and response to treatment

Sometimes cancer can be cured, while other times it can only be managed to limit the spread and prolong your pet’s comfort and life as much as possible. Aggressive cancers typically require more aggressive treatment, which may cause more serious side effects and complications. Depending on the situation, euthanasia may need to be considered, especially when the type or stage of cancer makes successful treatment unlikely, the cost or demands of treatment are more than an owner is able to cover, or the pet’s quality of life is poor despite treatment. 

Your veterinarian will use their experience and what they know about your pet to provide their best estimate of what to expect from the various treatment options so you can make an informed decision. 

What can I do if my pet has cancer?

Advances in veterinary medicine mean that cancer is no longer a hopeless diagnosis. Many pets can enjoy months or even years of quality life with the right care. Your love and attention are vital parts of their journey.

If your pet is diagnosed with cancer, remember that you have options: 

• Educate yourself by learning about your pet’s condition and possible treatments.
• Ask questions and, if necessary, seek a referral to a veterinary oncologist.
• Ask your veterinarian whether there are any clinical trials investigating treatments for your pet’s condition.
• Work with your veterinary team to ensure your pet is as comfortable as possible.
• Consider joining a support group or talking to others who have faced similar situations.

Caring for a pet with cancer can be financially challenging, but some choices exist here as well. Be sure to ask your veterinarian about payment plans, financial assistance programs, clinical trials, and other options that may be available.