Cancer in Dogs: Symptoms, Types, and Treatment

As many people have had their lives or the lives of their friends or family touched by cancer, cancer can be a really scary diagnosis for pet parents.  

Cancer in dogs can take many forms.  

Some are straight forward, like a skin mass that is cured with surgical removal. Others are much more serious, like metastatic cancer that has spread throughout  the body. 

Dogs can get cancer, and while some types of cancer are obvious and easy to diagnose, others may be more insidious and require extensive tests to diagnose.  

Let’s explore several common cancer types in dogs. 

What Is Cancer in Dogs?

Cancer occurs when cells in your dog’s body divide without following the rule book.  

Normally, there is a system of check and balances for when cells should divide and when they should die.  

With cancer, this system fails, and cells are able to multiple problematically. They no longer listen to the body and stop dividing when they’re supposed to. They instead continue to divide and multiply.   

Depending on the type of cell that is growing and multiplying, you may see a mass form.  

When fat cells are affected, like in the case of a lipoma, you may see a large soft fatty mass on your dog’s skin. 

 When splenic cells are affected, your vet may appreciate a mass on the spleen pushing other abdominal organs back on their X-rays. 

Oftentimes, when abnormal cells are replicating, they damage the function of the affected organ. If there’s cancer in your dog’s bone marrow, it will not be able to do its job and make blood cells as efficiently as it normally would.  

This can result in blood work changes. 

Cancers can be locally aggressive.  

This means that they can get very large and destroy normal tissue around them. 

Alternatively, cancer can be metastatic. This means that the cancer will spread to other parts of the body causing problems in multiple systems. 

What Are the Most Common Types of Cancer in Dogs?

Masses and lumps in dogs are relatively common, but not all of them are cancerous. 

When a mass isn’t cancer, it is referred to as benign. In most cases, benign masses grow more slowly and don’t spread to other parts of the body, so they don’t pose a serious health threat. 

By contrast, cancerous masses are characterized by cells that can multiply. They are known as malignant tumors and may grow rapidly, spreading to other organs and parts of the body. This can cause serious health problems. 

How fast cancer grows and where it spreads depends on the type of cancer. 

Dogs, just like humans, can get cancer. 

In fact, about 25% of dogs will develop some form of cancer in their life and about 50% of dogs over the age of 10 will develop cancer. 

While this isn’t a complete list, let’s look at some of the most common types of cancer in dogs: 

• Anal sac adenocarcinoma. This cancer affects the anal glands, which are scent glands located in the rectum. It can metastasize (spread) to other parts of the body. 

• Hemangiosarcoma. This tumor often arises from blood vessels—meaning it can arise anywhere. However, it’s typically found in the heart, liver or spleen. It’s an aggressive type of cancer and has usually already spread by the time a diagnosis is made. 

• Lymphoma. There are several types of lymphoma that dogs can get, but the most common affects the lymph nodes. It’s one of the most common forms of cancer in dogs, but fortunately it’s the type most responsive to chemotherapy. 

• Mammary gland carcinoma. Female dogs have about five pairs of mammary glands, and these types of tumors are more common in unspayed females. Hormones like estrogen and progesterone play a role in mammary development and cancer formation. 

• Mast cell tumor. This is the most common cancer of the skin, which can be difficult to determine with sight alone since the appearance can vary. These tumors have a variable prognosis and can range from low to high grade—meaning they are less likely or more likely to spread to other areas in the body. 

• Melanoma. This type of cancer can occur on the skin or in the oral cavity; these tumors are typically malignant when found in the mouth and require aggressive surgery and/or combination of radiation and chemotherapy. They usually show signs associated with dental disease like bad breath and decreased appetite.  

• Osteosarcoma. This is the most common cause of bone cancer in dogs, which is highly aggressive and painful. This cancer commonly affects the legs of larger dog breeds.  Treatment often includes surgery followed by chemotherapy or radiation. 

• Transitional cell carcinoma. This is the most common type of urinary cancer, which usually affects the bladder the most and often causes symptoms like a urinary tract infection (UTI). 

Symptoms of Cancer in Dogs

Symptoms of cancer in dogs can vary. 

Some pups may have a lump or bump, inflammation, a wound that doesn’t heal, swollen lymph nodes, or abnormal bleeding. But many symptoms are nonspecific, including: 

• Unexplained weight loss 

• Fuller looking abdomen (belly) 

• Behavioral changes or other neurological issues like seizures or head tilt 

• Coughing or changes in respiration 

• Decreased appetite

• Exercise intolerance 

• Pale gums 

• Lethargy 

• Vomiting and/or diarrhea 

If you are even slightly worried about your pup—especially if you notice a change in behavior or find a new lump—schedule an appointment with your veterinarian for an exam. 

How Do Dogs Get Cancer?

Cancer in dogs often occurs for unknown reasons. However, it can be influenced by many factors, including:  

• Old age 

• Viruses and infections, like canine papilloma virus or bartonella 

• Chemical and toxin exposure 

• Genetics 

• DNA mutations 

• UV damage or other environmental triggers, like chronic exposure to cigarette smoke or various chemicals like pesticides or plastics 

• Obesity 

How Veterinarians Diagnose Cancer in Dogs

To diagnose cancer in dogs, a veterinarian will perform a physical exam to look for any abnormal or unexplained lumps, bruises, or masses large enough to be felt during palpation (the act of pressing on the surface of the body to feel the organs or tissues underneath). 

Your veterinarian may want to perform an FNA (fine-needle aspirate) of the mass. 

Alternatively, a biopsy may be performed and studied for type, malignancy, and grade. All of this provides insight into how the cancer may progress. 

Blood work and urine testing is typically recommended. 

Imaging with radiographs (X-rays) or ultrasound may also be needed to screen for masses in the chest or abdomen.  

Once diagnosed, your veterinarian may recommend additional tests or refer you to an oncologist for further testing and treatment, including staging (staging determines the extent the cancer has spread). 

This may include CT scans, bone marrow aspirates, or additional biopsies. 

The prognosis will vary depending on the type of cancer, grade, and stage. Usually, the higher the grade and greater the stage the worse the prognosis.  

Dog Cancer Treatment

Generally, there are three treatment options for cancer in dogs—surgery, radiation, and chemotherapy. 

Some cancers in dogs may respond to one type of treatment, while others may require a combination of some or all to achieve a favorable prognosis. 

A full cure is difficult to find in many types of cancer. For some, surgery may be curative. For others, treatment may be more geared towards increasing how much quality time you have with your pup.   

Some medications used to treat cancer include: 

• Carboplatin 

• Chlorambucil 

• Cyclophosphamide 

• Doxorubicin 

• L-asparaginase 

• Lomustine 

• Mitoxantrone 

• Toceranib (Palladia) 

• Prednisone 

• Vinblastine 

• Vincristine 

Dog Cancer Prognosis

Treating and managing cancer in dogs is different than treating cancer in humans, as there are different goals and expectations. 

The goal is to maintain a good quality of life, and medication dosages and frequency of administration are typically less than what a human would be prescribed, which minimizes side effects. 

The most common side effects are: 

• Decreased appetite 

• Lethargy 

• Vomiting 

• Diarrhea 

However, serious side effects—like bone marrow suppression and infections—can occur. With few breed exceptions, dogs don’t lose their hair. Dogs with curly or wiry hair may be prone to experience hair loss, while other dogs don’t. This includes Poodles and Terriers. 

While they are going through chemotherapy, it’s important to keep your dog comfortable and manage their pain appropriately. To keep your pup comfy, make sure you offer cozy dog blankets and soft dog beds. 

This means collaborating with your veterinarian, adhering to proper appointment recommendations, and following through with blood work monitoring and other testing.  

Caring for a dog with cancer is a challenge and can be burdensome and emotional but remember to take advantage of each day’s opportunities for play, bonding, and love.  

Knowing when it’s time to stop treatment or consider humane euthanasia is both variable and individual for all pets and pet parents. 

Many factors such as prognosis, metastasis, risks of treatment, cost, and quality of life should be considered. 

But when it comes to quality of life, which can be subjective, keep in mind the five freedoms: 

1. Freedom from hunger and thirst 

2. Freedom from discomfort 

3. Freedom from pain, injury, and disease 

4. Freedom to express normal behavior 

5. Freedom from fear and distress 

Your veterinarian is the best resource when it comes to knowing when it’s time. Your vet is trained in end-of-life care and disease outcomes, and there are many resources and tools that can help when it comes to making this difficult decision.  

How To Prevent Cancer in Dogs

Unfortunately, there’s very little a pet parent can do to prevent cancer in dogs from occurring. 

Routine checkups and evaluation of any new lumps or unexplained illness should immediately prompt a veterinary visit. 

There are a few small ways you can limit your dog’s risk of getting cancer, such as: 

• Limit sun and UV exposure 

• Have your dog spayed or neutered 

• If your dog is a breed predisposed to certain tumors, bring them for more frequent screenings 

• Keep your home completely smoke and tobacco-free