Nothing seems to strike more fear into the hearts of dog parents than the dreaded “C” word. Hearing that your dog has been diagnosed with Cancer is a heart-wrenching experience, bringing with it an entire range of emotions – fear, disbelief, anger, denial, and grief – that can feel overwhelming.

Cancer in dogs is one of the leading causes of canine death, especially in older dogs. Studies have shown that approximately 50% of dogs over the age of 10 years will develop cancer at some point in their lifetime, and of those dogs, approximately one in four will eventually die from it¹. How cancer affects an individual dog depends on the type of cancer present, the age of the dog, environmental factors, and that particular dog’s genetic makeup.

The increasing rate of cancer in dogs is thought to be due in part to the fact that our dogs are simply living longer. Advancements in veterinary care, nutrition, and disease prevention are extending the lives of dogs well beyond what has been possible in years past. But with this good news comes the bad news – as our dogs get older, they are also at a higher risk for developing cancer.

What Exactly Is Cancer, Anyway?

Simply put, cancer is a disease where the DNA (genetic code) of a normal cell becomes damaged, causing the cell to mutate. This damage can be caused by a virus, radiation, exposure to chemicals (such as pesticides or herbicides), or some types of hormones. The negative effects of these agents build up over the years, which could explain why so many cancers affect older dogs.

The damaged cell begins to go rogue and starts replicating itself, unchecked. The resulting cells then invade surrounding tissue, where they induce new blood vessels to grow around them to supply them with nutrients. This is what allows the cancer to spread (or metastasize) to other areas of the body.

Cancer is known as a “multifactorial” disease, which means there is no single known cause. Both environmental and hereditary factors can contribute to the development of cancer in dogs.

The Most Common Types Of Cancer In Dogs

Although many different types of cancer can develop in dogs, these are the most common (in no particular order).

Lymphoma

Also called lymphosarcoma, lymphoma is a cancer of the lymph nodes and lymph tissue, but can also involve the liver, spleen, bone marrow, and other organs. Lymphoma is one of the most common cancers in dogs, and is the most commonly treated cancer in veterinary medicine.

Lymphoma is an aggressive cancer, but if caught early, it has one of the most successful treatment rates. Lymphoma is usually treated with a combination of chemotherapy drugs and the steroid prednisone. This protocol results in remission in approximately 60-90% of cases, with a median survival time of 6-12 months. In approximately 20-25% of cases, some dogs can live 2 years or longer after treatment. Without treatment, however, prognosis is very poor.

Mast Cell Tumors

Mast cells are immune cells in a dog’s body that are responsible for allergic reactions. They can be found in all tissues of the body, but when they are cancerous, they usually form tumors on the skin. These quickly-growing tumors range from benign (non-cancerous) to extremely aggressive and malignant (cancerous). When malignant, they have a tendency to spread to other areas of the body, so they should always be addressed immediately when they are found.

Treatment for a mast cell tumor usually includes surgical removal of the tumor. If the growth is benign and all of it has been completely removed, no further treatment is recommended. However, if the tumor is cancerous, treatment options involve radiation, chemotherapy, and steroids to suppress the immune system. Treatment and prognosis depends on how advanced and aggressive the tumor is.

Osteosarcoma

Osteosarcoma is cancer of the bone. Although it can occur anywhere in the body, it’s more commonly found in the leg bones of large and giant breed dogs (although dogs of any size can develop osteosarcoma). The most common symptom is pain and swelling in the affected leg, along with lameness that gets progressively worse.

Treatment for osteosarcoma in the leg is usually amputation of the affected limb, followed by chemotherapy. However, osteosarcoma is one of the more aggressive cancers in dogs, and it has a tendency to spread to other areas of the body such as the lungs and liver. Usually by the time swelling and lameness become apparent, the cancer has already begun to spread, making the prognosis for dogs with osteosarcoma very poor.

Hemangiosarcoma

Hemangiosarcoma is a highly malignant cancer that develops in the endothelial cells, which line the body’s blood vessels. It mainly affects the spleen, liver, heart, and skin, but can spread anywhere in the body. Hemangiosarcoma is common in Golden Retrievers, Labrador Retrievers, and German Shepherds.

This cancer develops very slowly and is essentially painless until it begins creating problems, so it’s often not caught until the disease is well-advanced. Many dogs actually die from severe internal bleeding before the cancer is even diagnosed. Treatment involves removal of the affected area, followed by chemotherapy and radiation. However, prognosis for most forms of hemangiosarcoma (with the exception of the skin form) is very poor – less than 50% of treated dogs survive longer than 6 months.

Mammary Cancer

Just like humans, dogs can develop breast, or mammary, cancer. Mammary tumors most commonly affect older, unspayed female dogs, or female dogs who were not spayed until after their second heat cycle.

Approximately 50% of mammary tumors are cancerous, while the other 50% are benign. Treatment involves surgically removing the tumor. Sometimes follow-up chemotherapy may be recommended. The good news is, if mammary cancer in dogs is diagnosed early, and the cancer has not yet metastasized, surgically removing the tumor oftentimes will completely remove all the cancer, giving the dog an excellent prognosis.

Oral Cancer

Oral cancer involves tumors of the mouth and throat. This type of cancer ranges from mild to extremely aggressive, so any oral tumors found in a dog’s mouth should be biopsied to find out the type and extent of the disease. Many oral tumors are found during routine veterinary teeth cleaning, another good reason to have regular dental exams performed on your dog.

Oral cancers are usually treated by surgically removing the tumor, with some requiring follow-up radiation depending on the type of cancer present.

Squamous Cell Carcinoma

This is one of the most common cancers found in dogs. Squamous cell carcinoma is a malignant cancer, mainly found in 3 areas of the body: the skin cells of the epidermis, in the mouth (on the gums or tonsils), and around the nail beds of the toes.

Complete surgical removal of the affected area is the treatment of choice for this cancer. Fortunately, fewer than 20% of cases metastasize, but it depends on the type and location of the tumor.

Melanoma

Melanoma arises from pigment-producing cells in the body called melanocytes. There are several types of melanoma found in dogs. With a few exceptions, almost all are malignant, and are found in the mouth, skin, and eyes.

Most malignant melanomas grow rapidly and spread quickly to other parts of the body like the lymph nodes, lungs, heart, spleen, and brain. Chemotherapy is ineffective against malignant melanoma. Radiation therapy can be used to help extend the life of a dog diagnosed this form of cancer, but once it has metastasized, little can be done.

Symptoms Of Cancer In Dogs

It’s important to be familiar with the warning signs of cancer. These include:

• Lumps, bumps, or any abnormal growth or swelling that doesn’t go away
• Rapid weight loss
• Unusual foul odor, especially from the mouth, nose, skin, or rectal area
• An open sore that won’t heal
• Any dramatic change in appetite
• Difficulty swallowing or eating
• Sudden onset of lameness, not related to an exercise injury
• Pale gum color
• Weakness and fatigue
• Swollen lymph nodes (especially in the neck, and around the hock area of the rear legs)
• Coughing, wheezing, or shortness of breath
• Chronic bleeding or discharge from the mouth, nose, ears, or rectal area
• Abdominal bloating or distension
• Black, tarry stools
• Chronic vomiting or diarrhea
• Fever
• Difficulty urinating or defecating
• Pain anywhere in the body
• Collapse

Also watch for any behavioral changes that are out of the ordinary. Is the dog sleeping in rooms he typically doesn’t go into, or hiding in unusual places? Also, a calm dog who suddenly acts snappy or aggressive may be in pain.

How Is Cancer In Dogs Diagnosed?

If you or your veterinarian find an obvious tumor or mass, the first step is to take a cell sample from the tumor. This is done by either sticking a needle into the tumor and drawing up some cells, or with a surgical biopsy. The cells are then sent to a lab, where a pathologist can examine and identify them.

Radiographs (x-rays) or ultrasound can also be used to evaluate whether there are any suspicious-looking growths in the lungs, liver, spleen, or abdomen. Your veterinarian can also run blood tests, which will show any abnormalities that could indicate cancer somewhere in the body. The vet may also take a urine sample for urinalysis.

Treatment Options For Cancer In Dogs

The goals of treating cancer are two-fold: to remove all cancerous tissue whenever possible, and to prevent any cancer cells that are there from spreading.

For many cancers (especially if they are caught early), there are several different types of treatment options available to either wipe out the cancer completely, or keep it at bay for a long enough period of time to extend the dog’s length and quality of life for as long as possible. Which method is used will depend on the type of cancer cells that are identified.

1. Surgical excision – surgical removal of the tumor and any surrounding tissue that may have been invaded.
2. Chemotherapy – the use of chemotherapeutic drugs (given either orally or through an IV) designed to poison and destroy all rapidly-dividing cells in the body.
3. Radiation therapy – the use of highly-targeted radiation to kill malignant cancer cells. Radiation therapy is particularly helpful for targeting cells deep in the brain and nasal cavity, areas that were previously inaccessible to surgeons.
4. Immunotherapy – the use of specialized drugs to stimulate the body’s immune system to recognize cancer not as the body’s own tissue, but as an invading disease that needs to be destroyed.
5. Cryotherapy – using extreme cold to freeze and remove tumor tissue.

Unfortunately, with chemotherapy and radiation, normal cells in the body can also be damaged during treatment. This can lead to possible side effects such as nausea, vomiting, diarrhea, lethargy, weakness, and loss of appetite. These effects are usually temporary.

What’s The Prognosis For A Dog With Cancer?

The prognosis for a dog with cancer can be extremely difficult to state with any degree of certainty. There are many factors that must be taken into consideration: the type of cancer, location of the tumor, age of the dog, whether the cancer was caught early or in later stages, or if the cancer has already spread.

The good news is that modern cancer management doesn’t just involve killing cancer cells. Successful management of cancer in dogs includes pain control, good nutritional support, physical therapy, protection against stomach ulcers, and can also include the use of alternative therapies such as acupuncture, massage, herbal therapy, and diet therapy.

So what’s the overall success rate for dogs who undergo treatment for cancer? According to Dr. Dave Ruslander, veterinary oncologist and past president of the Veterinary Cancer Society, “Overall, for the malignancies that we see, it’s probably in the 60-plus percent range.” The patients who have discernible lumps and bumps removed seem to have the best prognosis, as do dogs who are treated in the early stages of lymphoma.

However, sometimes even dogs who are treated cannot achieve remission. For these dogs, many pet parents opt out of further treatment, and instead take their dogs home for palliative care (providing the dog with relief from pain and physical stress) until the dog’s quality of life declines to the point where euthanasia is the most humane option.

So What Should You Do If Your Dog Is Diagnosed With Cancer?

As a former veterinary technician, I was often asked by clients what I would do if it were my dog who was diagnosed with cancer. Having dealt with cancer in my own pets, I always answered truthfully: Ask yourself what is best for YOUR DOG. Not you, your veterinarian, your family, or your friends. Your dog. Every dog, like every cancer, is different. You must make the best decision you can based on the knowledge that you have, not only of the cancer itself and the treatment options, but of every unique and individual factor that makes up your dog.

The veterinary definition of successful remission usually means about 6 months. Your dog’s remission could be 3 months, or it could be 3 years. It’s important to remember that, unless the cancer was completely cured by surgical excision, in most cases cancer will eventually win the battle – it’s just a question of when. That doesn’t mean treatment is hopeless – far from it! But whatever you decide, don’t let guilt factor into your decision. Be the advocate for your dog. Your dog may not be a good candidate for treatment due to advanced age, other health issues, aggression, anxiety, or fear. Or perhaps, your love for your dog notwithstanding, due to circumstances beyond your control your family is simply not able to afford thousands of dollars for treatment. Every person’s situation is different.

Whatever you decide, examine your heart and do what you know is right for your dog. And only you know what that looks like.

Can Cancer Be Prevented?

The good news is, improvements in nutrition, medical care, disease prevention, and diagnostic procedures have helped today’s dogs actually live to ages when accumulated DNA damage can cause problems such as cancer. The bad news? It goes without saying.

So what can we do about it?

While not all cancer can be prevented, there are things you can do to help decrease your dog’s risk of developing cancer. Consider spaying or neutering your dog between 6 and 12 months to help prevent reproductive cancer. If you’re a smoker, either quit smoking or take steps to reduce your dog’s exposure to second-hand smoke.  Make sure your dog stays at a healthy weight, has regular veterinary exams, and gets frequent exercise and good nutrition.

But the best thing you can do is to be diligent about monitoring your dog’s health. By far one of the most common ways pet parents detect cancer is by finding a lump or mass on their dog. Early detection of cancer, before it has a chance to spread, is critical for successful treatment.

If you do find something unusual on your dog, or if he is showing any of the warning signs of cancer, have him checked out immediately by your veterinarian. The “wait and see” approach is not a good policy to use when it comes to possible cancer in dogs.

And if your dog is diagnosed with cancer, always get a second opinion, preferably from a veterinary oncologist, to discuss all your options so that you can make the best decision possible for your dog.

Have you ever had a dog who was diagnosed with cancer? If so, what did you do? Please share your story with us in the comments below!

¹ Oxford Journal, “Domestic Dogs and Cancer Research: A Breed-Based Genomics Approach”, 2014.

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