While our furry companions are the last to deserve the fate of a cancer diagnosis, unfortunately, that’s not always how it works out. Dogs can get cancer the same way that humans can, with no warning and sometimes without clear reasoning as to why. Thankfully, between the advancements in medical practices for both humans and dogs, many of the cancers that affect patients—human and canine alike—can be treated.
Although there is no way to know the exact reason why one dog may be diagnosed with cancer while another isn’t, we are able to take note of trends in the dogs that develop cancer to find patterns that lead to a predisposition to developing it.
There are a few reasons that canine health researchers think older dogs are more likely to get cancer. Some think that the dog’s immune system gets weaker over time and is not able to defend as efficiently against cancerous cells. Others believe that older dogs have spent more time encountering carcinogens and that, over time, the amount of those carcinogens in the body leads to a higher probability that the dog will develop cancer. In either case, dogs over 10 years old are almost twice as likely to develop a form of cancer and 45% of dogs over the age of 7 are likely to pass due to cancer. 1,2
There is a mathematical correlation that female dogs are more likely to develop cancer than male dogs, though that amount comes more from the fact that mammary cancers are more likely to present in female dogs than in their male counterparts. Mammary cancer is the most commonly diagnosed cancer in female dogs who are over the age of seven and who were never spayed; male dogs will rarely develop this type of tumor. Other cancers are not as easily divided by gender in terms of the likelihood of development. 2
A trend has been found in female dogs who were neutered before their first heat to have a lower likelihood to develop cancer later on in life. In contrast, dogs that were neutered after their first heat or were not neutered at all have shown a greater increase in the probability of developing cancer within their lifetimes.2
There are several known health complications that can arise when a dog is overweight. Obesity in dogs can lead to an increased risk of mast cell tumors, mammary tumors, and some bladder cancers. While this increased risk does not always mean that obesity in your dog will lead to developing cancer, protecting their weight through proper portioning and regular exercise is very beneficial.2
Diet can also make a difference in a dog’s chances of developing cancer in their lifetime. While a majority of dogs in America are fed dry food or other commercially processed foods, it is important to consider where the food is coming from, the ingredients included in it, and the way that the food is stored to protect your pet from any potential carcinogens. Some pet foods may contain cancer-causing toxins like preservatives, fillers, or other chemical additions to the food. And if food is not stored effectively or protected from the development of mold, the mold byproduct aflatoxin may be able to make a home in your dog’s food, raising their cancer risk exponentially.2
The most obvious trend towards cancer development comes from one of the easier ways to track dog populations. Dog breeds are notable organizations of genetic patterning. Studies are regularly conducted on why a certain breed may develop a specific cancer more often or regularly than any other breed. Typically, purebred dogs are the most likely to develop cancer over their mixed-breed counterparts, and of those, it has been shown that some specific breeds have an even higher risk for specific cancers rather than just the disease itself.
Breeds that are known to more likely to develop a specific type of cancer in their lifetime include:1,2,3
1. Golden Retrievers and Labrador Retrievers
2. German Shepherds
4. Bernese Mountain Dogs
Any dog can have the misfortune to develop any kind of cancer, even if it is not a breed that is known to be predisposed to the development of the disease. And while we discuss the more prevalent cancers here, it is important to note that there are many more, less common forms of the disease that may not be included on this list but are still a possibility for your pet to develop.
Lymphoma is one of the most common types of cancer diagnosed in dogs. It is cancer of the lymphatic system, which is part of the dog's germ-fighting network or the white blood cells that work in the immune system. Because those cells are spread throughout the body, more often than not lymphoma is a systemic cancer and not one that can be treated locally. While there may be a noticeable centralized location like a swollen lymph node, there is a higher chance that the cancer is affecting more of the body than is visible.2,4,5
Lymphoma is treated most effectively with a multidrug chemotherapy protocol.
Hemangiosarcoma is a cancer that affects the cardiovascular system. Blood vessels inside the heart are lined with cells called endothelial cells, these are the cells that are affected when a dog has hemangiosarcoma. The most common place for a tumor to develop with this particular type of cancer is in the spleen, liver, right atrium of the heart, and skin. Although, as with most cancers, it can develop outside of the expected areas as well.
Hemangiosarcoma is difficult to diagnose at the beginning of its development, so often the first avenue of treatment is to remove the tumor surgically and use the surgery to complete a biopsy to fully diagnose it. After surgery is completed, a chemotherapy treatment may be given as well to ensure that any remaining cancer cells in the body are removed.2,4,5
A mast cell tumor is one of the most common skin cancers in dogs. These are slightly more difficult for a pet owner to identify on their own without testing as they can appear in many different ways on the skin. Mast cells in the body are a part of the immune system that relates to the way a body handles an allergic reaction. When those cells become cancerous they turn into a mast cell tumor.
Mast cell tumors are, thankfully, not very likely to spread to other parts of the body with 60-70% of all dogs with a mast cell tumor having no sign of spread. Treating a mast cell tumor that has not spread typically consists of surgery and, depending on the severity, an addition of radiation therapy and/or chemotherapy.2,4,5
Melanoma is a cancer that affects the cells in the body that create pigment, the melanocytes. Because the affected cells create pigment, melanomas often appear as darkly colored masses, typically in the dog’s mouth (mucocutaneous junctions), nailbed, or the areas where hair-covered spaces meet those without hair—such as the lips, and occasionally in an eye. Melanomas are more often not cancerous when they are located near the mucocutaneous junctions but are more likely to be cancerous when found on the nailbed or mouth.
Melanomas are typically treated with surgery and occasionally radiation therapy. Whether cancerous or not, chemotherapy is not often a relied-upon treatment unless the melanoma is returning after a previous treatment. In that case, chemotherapy is used as a rescue treatment.2,4,5
Osteosarcoma is the most common bone cancer in dogs. It more often affects larger breeds than their smaller counterparts. Osteosarcoma typically develops in the limbs but it can also appear in the skull, ribs, vertebrae, and pelvis, as well as some non-bony tissues such as mammary glands, spleen, liver, and kidneys.
When osteosarcoma develops in the limbs, the first line of defense for treatment is usually amputation. Luckily, dogs are very resilient in the face of amputation and are quick to adjust to their new arrangement. Though some tumors will have outside factors that will make them not viable for amputation, surgical removal of the tumor and replacement with a custom titanium implant is the next best option.2,4,5
Lung cancers are not one of the more common cancers that dogs will face, making up around 1% of all diagnoses. For the few that do develop the disease, some dogs with tumors in their lungs will not show any symptoms while others may show noticeable signs of difficulty breathing or coughing, and other general signs of health distress.
Lung cancers are often treated with surgery first, then potentially with radiation therapy. Radiation therapy is occasionally combined with a chemotherapy regimen depending on the severity of the cancer’s spread.5
Mammary tumors are the most common kind of cancer diagnosed in non-spayed female dogs, especially between the ages of 8-11 years old. Only about half of all of the mammary tumors found will be cancerous, and often mammary tumors are found by accident because they don’t usually cause symptoms.
Mammary cancer is typically treated with surgery when there is only one tumor and no sign of spread to other parts of the body. If there are multiple tumors, there may be a need to remove some of the glands in the mammaries, and sometimes all of them—depending on the spread of the tumors.5
As an observant pet parent, you’re likely to notice if your dog is acting abnormally. If there’s any reason that your dog seems to be out of sorts for a longer period of time than what you can explain, it’s never an issue to reach out to your vet to see if there might be something going on with their health.
Some more specific signs that your dog may have cancer or another health concern include:4,5
As with any medical decision, the best option is going to be the one that is the most effective for your pet and the specific kind of cancer that they have. For some cancers, the best treatment will be surgery, for others, surgery may not have any impact. It’s always great to do your own research, but trust that your veterinary oncologist will have your best interest in mind.
Depending on the severity and location of the cancer that develops in your dog's body, some patients may be able to completely remove the cancerous cells from their body with just surgery alone. For external and localized tumors, surgery is often the first defense.5,6,7
Chemotherapy is the only treatment option that can effectively treat cancer cells throughout the whole body at one time. For dogs that have encountered spread with their cancer diagnosis, meaning the cancer is not just in the one spot that it originated in the body, chemotherapy is often a go-to treatment because it can help identify and neutralize cancer cells throughout the body.5,6,7
Radiation therapy is the use of the same technology as an x-ray machine at a higher dosage to destroy cancer cells. The radiation targets the gene in the cell that is mutated—the mutation makes the cell divide rapidly and therefore cancerous. Radiation therapy is often used in tandem with some of the other aforementioned treatments, though radiation on its own has still been known to visibly reduce the size of a tumor.5,6,7
Combination therapy is just like what it sounds, combining two or more anticancer drugs, or two or more treatment methods, that target cancer cells more efficiently in the body. This is one of the most common approaches used to treat cancer in pets because it allows the patient to uphold their quality of life through treatment and prioritize their wellbeing both emotionally and mentally, as well as improving their physical health.5,7