Cancer in Dogs

Cancer is one of the most frightening diagnoses for a guardian. Sometimes called “the emperor of all maladies,” a cancer diagnosis can be heartbreaking and lead to stress and confusion for dogs and their guardians.

However, there are many cancers, and a cancer diagnosis is not always terminal. In fact, despite over one in four dogs developing cancer in their lifetime, many of these dogs live years beyond prognosis with the proper treatment and care. 

medicus illustrations

What is Cancer?

Cancer is caused by the uncontrolled growth of cells in a dog’s body. These cells can originate in any of the body’s tissues, and they can start multiplying almost anywhere.

Normally the healthy cells in the body grow and multiply in a controlled manner through a process called cell division. Cell division forms new healthy cells as the body needs them. When the healthy cells grow old or become damaged, they die, and then new cells take their place.

However, sometimes this structured process breaks down, which results in abnormal or damaged cells growing and multiplying when they shouldn’t. These uncontrolled cells may form tumors. Tumors are lumps of tissue, and they can either be cancerous or not cancerous. Tumors are often described as either malignant (cancerous) or benign (not cancerous). Many kinds of cancers form tumors. However, cancers of the blood, such as leukemia, typically do not.

If cancer is not found and stopped in time, it can spread and affect other tissues in the body. Half of dogs over 10 years old will be diagnosed with cancer, the leading cause of death for dogs 10 years and older. 

However, about half of all cancer in dogs is treatable if it is treated and stopped in its earlier stages.*


Types of Canine Cancer

There are over 100 types of cancer seen in canines. * 



Some are much more common than others, and some are more well-known. Some of the most notable kinds of cancer seen in dogs are:

This is a cancer involving white blood cells called lymphocytes and of lymphoid tissues. Lymphoid tissue is normally present in many places in the body, including lymph nodes, spleen, liver, the gastrointestinal tract, and bone marrow.

Lymphoma is actually a term veterinarians use to describe an entire group of cancers which stem from when lymphocytes become cancerous. They collectively represent approximately 7-14% of all cancers diagnosed in dogs, with some data showing they may represent closer to 20% of all canine cancers.*

There are more than 30 categories of lymphoma that can develop in a dog’s body. It is most common in dogs from 6 to 9 years old, but it can happen in younger dogs too.** Dogs with compromised immune systems are more susceptible to lymphoma. Exposure to herbicides or industrial chemicals are other risk factors.

Lymphoma often first appears as swollen lymph nodes under the neck. Other places are in front of the shoulders or behind the knee. Some forms of lymphoma may be internal and cannot be felt externally. Lymphoma is generally considered treatable depending on the type.



Hemangiosarcoma is a cancer of the blood vessel lining, and it is a highly malignant cancer that can spread very rapidly, causing tumors almost anywhere in the body. However, it is most often found in a dog’s heart and spleen. Sadly, many times it is in an advanced stage before it is diagnosed.

It occurs more commonly in middle aged or older dogs, as well as certain breeds. Hemangiosarcoma represents 0.2% to 3% of all canine cancers. Unfortunately, hemangiosarcoma is a very difficult cancer to spot and dogs often don’t have any visible signs or symptoms until the disease has progressed. Most dogs diagnosed with hemangiosarcoma will pass from it within six months.*


Mast cell tumors are a type of tumor consisting of mast cells* which most commonly form masses or lumps in the skin. However, they can also affect other areas of the body, including the spleen, liver, intestine, and bone marrow. They are quite common in dogs, and account for approximately 20% of all skin tumors in dogs.** Mast cell tumors can be very invasive and often regrow after surgical removal. Some may also spread (metastasize). They can arise from any skin site on the body and can have a variety of appearances. Certain breeds of dogs are at an increased risk for developing this tumor, which suggests that genetics are most likely a cause.

*Mast cells reside in connective tissues, especially the vessels and nerves close to the external surface of your dog, including the skin, lungs, nose, and mouth. Not all mast cell tumors are malignant. Mast cell tumors are usually on the skin but sometimes in other organs. This type of cancer in dogs can be cured if the tumor is found early and completely removed.


Osteosarcoma is the most prevalent form of bone cancer, and it represents about 85% of all bone cancers in dogs. The first sign you’ll likely see is persistent lameness or swelling. It’s more common in middle aged dogs. Large breed dogs are most at risk for osteosarcoma.* Osteosarcoma routinely attacks the long bones in the limbs but can affect any bones. It often progresses quite rapidly by spreading to the lungs, the lymph nodes, and other bones. Because this cancer is aggressive and spreads extremely rapidly, amputation of the affected limb is recommended, followed by chemotherapy to treat any spreading.



Bladder cancer is fairly rare, and makes up about 1-2% of all dog cancers.* Some breeds are more at risk for this form of dog cancer than others. This is a somewhat slow developing dog cancer, and symptoms might not show for 3 to 6 months. Two common symptoms are urinary obstruction and bleeding.

Bladder cancer actually has two formal names: Transitional cell carcinoma or urothelial carcinoma. Lawn chemicals are a known risk factor for bladder cancer in dogs.** Transitional cell carcinoma is the most common tumor type found in the urinary system. Though it is often located in the area of the bladder where the ureters come from the kidneys intersect with the urethra, it can happen in any part of the urinary system, including the prostate gland in male dogs.







Mammary gland carcinomas (the dog equivalent to breast cancer) are the most common tumors in unspayed female dogs. There are often multiple tumors that develop, which are commonly overlooked since they usually appear as small nodules around the nipple and can’t easily be seen. Mammary gland carcinoma is relatively common in dogs and can actually happen in male dogs as well.  About 40-50% of female mammary tumors are malignant.* When male dogs get them they’re usually malignant. 


Melanoma is one of the most common oral cancers seen in dogs and frequently is seen in breeds with dark tongues and gums. It is the most common malignant tumor in a dog’s mouth. Melanomas come from pigment-producing cells called melanocytes, which is why they are seen more commonly in darker pigmented dogs. They can take on different forms in different locations. 80-85% of melanomas are found in the mouth (and often metastasize), 15-20% of melanomas are found in the nail bed.* They can be found in the skin and eyes but those tend not to be malignant. Signs of melanomas can be new lumps, changes seen in existing bumps, changes in skin color, and mouth issues like swelling, drooling, foul odor, loose teeth, inflamed gums, or trouble eating.




Common Signs of Cancer in Dogs

Cancer is a disease that tends to have a better outcome and survival rate the earlier it is diagnosed. As a result, it is very important for guardians to know the warning signs and to get their aging dogs regularly screened for cancer.

Each type of cancer affects the body differently, though many of the signs of cancer can be similar at first. Two of the most common signs to look for are growing lumps or sores that fail to heal.


Warning signs of cancer in dogs include:

  • Persistent or abnormal swelling
  • Development of abnormal lump(s) underneath the skin
  • Sores and wounds that do not heal
  • Loss of weight and/or loss of appetite
  • Bleeding or abnormal discharge from any body opening, such as the nose, mouth, or anus
    • This includes bleeding, vomiting, and diarrhea
  • Difficulty eating or swallowing
  • Coughing or difficulty breathing
  • Lethargy or loss of stamina
  • Persistent lameness or stiffness
  • Abnormal odors emanating from the mouth, ears, or any part of the body
    • Tumors in the mouth, nose, or anus can lead to bad or unusual smells.
  • Difficulty urinating or defecating
  • Neurological signs that don’t improve with treatment

Some of these symptoms may result from other diseases and disorders or aging and might not mean your dog has cancer. However, getting your dog to the vet to get checked out as soon as possible is essential, especially if your dog shows multiple of these symptoms.

What Causes Cancer in Dogs?

Often veterinarians never know exactly what caused a dog to develop cancer. Cancer is a disease with numerous potential causes and contributing factors.

Some potential causes of cancer are:

  • Chronic Inflammation
    • Oxidative stress is one of the leading causes of cancer
  • Genetics and Family History
  • Exposure to Environmental Carcinogens (cancer-causing agents)
  • Many environmental toxins have been linked to cancer in both dogs and cats
  • Some well-known pollutants that are known carcinogens are:
    • Second-hand Cigarette Smoke
    • Chemical flame retardants

    • Herbicides and insecticides

    • Household chemicals such as cleaners

    • Preservatives and toxins in food

    • Heavy metals found in the environment 

  • Viruses

    • Some viruses can induce tumorigenesis (the creation of cancer)

  • Hormones

    • Sex hormones can play a role in certain cancers

  • Radiation

  • Poor Diet and Nutritional Imbalances

  • Obesity

    • Often leads to inflammation

  • Chronic Stress

    • Often overlooked but chronic stress lowers immune function in addition to causing inflammation 

Nickel, uranium, benzidine, benzene, radon, vinyl chloride, cadmium, and asbestos are all common substances that have been identified as carcinogens.

How is Cancer Diagnosed and Treated?

Many cancer signs such as weight loss, anorexia, lethargy, and changes in behavior can be seen with other diseases, so a wellness check complete with blood and urine tests is needed for a diagnosis. If there are any lumps found, then a veterinarian will aspirate or biopsy it to see what kind of lump it might be, and if it is malignant, surgery will be advised. Preventing and resolving inflammation, eliminating cancerous cells while keeping them from spreading, and supporting the body are the primary goals of cancer treatment. 

Some cancers can be treated by simply removing the cancerous tumor or tumors via surgery. Others require chemotherapy or radiation therapy. Treatment options depend on the type of cancer, its location in the body, and the stage of cancer. 

The stage of cancer can be determined by how much it has metastasized (spread) throughout the body. 

Diet’s Role in Cancer Support

Proper nutrition is the most important foundation for healing and supporting a dog with cancer. Unfortunately, nutrition is often overlooked during conventional cancer treatment despite how critical it is to overall health and well-being. 


For the carnivorous dog, a proper diet means eating species-appropriate real whole foods. When your dog’s body is supported with all the essentials needed to maintain healthy cells and repair damaged ones, healing can begin from the inside out. 

A Cancer Support Diet aims to nourish the body with clean wholesome real food, provide free radical fighting antioxidants and phytonutrients, reduce fuel for the cancer cells, and to significantly lower inflammation throughout the body with healthy fats.

Holistic veterinarians frequently recommend a diet that is low-carbohydrate, high in protein, moderate to high in healthy fats (especially omega-3 fatty acids), and very high in antioxidants for cancer patients. 


A good cancer diet can accomplish several important tasks: 


1). Feed your dog’s healthy cells foods dense with nutrition to keep them strong 

2). Eliminate foods that feed the cancer or do not give your dog any nutritional benefit 

3). Clean food to lighten the load on the immune system 

4). Flood the body with dietary antioxidants 

5). Provide high levels of healthy fats 


From the pet who has cancer but otherwise appears in good weight and is eating fine to the older cancer patient who has a loss of appetite and muscle wasting, there are many different types of cancers and cancer patients can vary widely.For the severely affected pet, a large goal of nutritional management is selecting a food both highly palatable and energy dense because every bite matters in supporting their overall body health, quality of life, and ability to continue to fight. 


All ingredients in your dog’s food should be fresh, highly bioavailable, easily digested, and highly palatable.

The Importance of Real Whole Food Nutrition in a Cancer Support Diet

A cancer support diet aims to nourish the body with clean wholesome real food, provide free-radical-fighting antioxidants and phytonutrients, reduce fuel for the cancer cells, and significantly lower inflammation throughout the body with healthy fats. This can be done using balanced and whole food nutrition made from high-quality and clean ingredients.  


Some of these ingredients include:


Cancer cells tend to use carbohydrates or sugars as fuel. In fact, fast-growing cancer cells can use up to 200x the amount of glucose as a normal cell of the same type. Ketogenic diets target the Warburg effect, a biochemical phenomenon in which cancer cells predominantly utilize glycolysis (i.e. using glucose for energy). There are two forms of energy for cells, the most common being the use of glucose and the second form, ketone bodies through Gluconeogenesis, which forms ketone bodies from amino acids of protein. Some cancers cannot metabolize ketone bodies, due to mitochondrial dysfunction and down-regulation of enzymes necessary for ketone utilization, therefore, reducing the energy available to feed cancer cells.  

Also by reducing blood glucose, insulin and insulin-like growth factor, the drivers of cancer cell proliferation, are also reduced in the bloodstream. 


As research done at Colorado State University demonstrated, cancer cells had a preference for using carbohydrates in the diet for their source of energy. Since cancer cells utilize glucose from carbohydrates as fuel, it is important to limit the fuel so that the cancer cells’ growth will also be limited. Therefore, a diet higher in quality protein and fats (specifically Omega 3 fatty acids) supplies energy for the dog and not the cancer cells. Dogs with lymphosarcoma fed this diet lived longer than the dogs fed more carbohydrates, meaning there is a real possibility that a low carbohydrate diet could assist in cancer management. 

Nourishes the Body with Clean Wholesome Foods  

High-quality digestible animal proteins come from wholesome cuts of meats from healthy USDA-Inspected animals being used for human consumption. 


They should meet the same standards as human meat production, including:  

  • A healthy animal  
  • No antibiotic use prior to slaughter 
  • No chemicals or medicines administered prior to slaughter  
  • Humanely Slaughtered 
  • Processed according to USDA standards 
  • Stored according to USDA standards  


It is important to feed enough protein as cancer cells compete with the dog’s body for protein. Tumors take a lot of protein from other areas of the body which leaves less protein available for muscle growth, disease immunity, and wound healing. Therefore, some cancer patients still regularly eating lose weight and muscle mass and become thin.  


Omega-3 fatty acids help decrease inflammation throughout the body. All pets can benefit from them, but especially dogs with cancer.  Omega-3 fatty acids are some of nature’s strongest anti-inflammatories and are crucial for dogs. In addition to being anti-inflammatory, Omega-3 fatty acids are vital for immune and nervous system functions.  


Ground krill is a rich source of omega-3 fatty acids. And unlike larger fish oils, krill is so low on the food chain that they do not accumulate toxins like larger fish do. 


The ratio of Omega-6 fatty acids to Omega-3 fatty acids are important in the evaluation of a diet. Dry dog kibble diets tend to have omega 6 to omega 3 ratios in the range of 40:1. Medicus Cancer diets have high omega 3 fatty acid content and a healthy ratio of omega 6:omega 3 – .46:1 for the chicken-based cancer diet and .44:1 for the beef-based cancer diet. 


As research done at Colorado State University demonstrated, a diet higher in quality protein and fats (specifically Omega 3 fatty acids) supplies energy for the dog and not the cancer cells. Dogs with lymphosarcoma fed this diet had a statically significantly longer disease free interval and survival time. 

Antioxidants also have a big role in nutrition. Rich in antioxidants like flavonoids, beta-carotene, and polyphenols, superfoods contain the free-radical fighting power the body needs to reduce oxidative damage. The reactive oxygen species (ROS) that are formed during normal metabolic oxidation are determined to play a role in the development of some cancers. There is a growing body of evidence researching the link between dietary antioxidants and the role they play in hindering ROS and the negative effects on tissue. 


Superfoods include fruits or vegetables such as beets, broccoli, spinach, blueberries, tomato, avocado, cranberry, spirulina, sweet potato, barley grass & pomegranate. They are superfood because they are rich in healthy substances, especially antioxidants. The concentrated antioxidant sources allow for a smaller volume of these foods for the carnivore diet.


Broccoli is rich in glucosinolates. These compounds protect cells from DNA damage, make carcinogens inactive, induce cell death in tumors, prevent tumor blood vessels from forming, and provide anti-inflammatory effects. Broccoli is full of fiber, calcium, potassium, protein, beta-carotene, vitamin C, vitamin A, and vitamin D.  



Beets are rich in folic acid, potassium, fiber, and beta-carotene. The fiber content is high and is insoluble, which makes the body’s detoxifying process more efficient and supports healthy liver function.  



Supplementing dark leafy greens such as spinach has been shown to help dogs overall health and wellbeing. It contains numerous phytonutrients with antioxidant properties including flavanols such as spinacetin, patuletin, and jaceidin, as well as polyphenols like quercetin and luteolin. Spinach is also a source of alpha-lipoic acid (ALA), a powerful compound that may help scavenge free radicals.  


Tomato powder – High in fiber, lycopene, beta carotene, vitamin C and K.  


Avocado meal – A nutrient-dense fruit high in healthy fats and fiber. Plus, they boost the absorption of vitamins A, D, K, and E.  


 Spirulina – Rich in unique phytonutrients like phycocyanin, polysaccharides, and sulfolipids that boost the immune system.  

It also has natural carotenoid antioxidants that promote cellular health.  


Sweet potato – These root vegetables offer fiber, beta- carotene, and antioxidants, including vitamin C.  


Barley grass – A superfood alongside the likes of spinach, kale, and wheatgrass.  


Blueberries and Cranberries 


Berries such as cranberries and blueberries are full of antioxidants. The antioxidants in blueberries prevent cell damage, and the anthocyanins or dark pigments that give the fruit its color have anti-inflammatory properties, as well.  


Pomegranate – High in Vitamin C, Vitamin K, and polyphenols, pomegranate lends more antioxidants to help fight against free radicals.  



Nourishing the body with clean proteins, low carbohydrates, and antioxidant-rich whole foods can support dogs with cancer, giving them what they need to fight and perhaps recover. 

Note: The information provided is educational and does not represent medical advice regarding pets. Please see your vet for an accurate diagnosis of your pet’s condition.

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