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How Can I Tell if My Dog Has Cancer?

Pet Health and Safety  •   Erin Tursam  •   Nov 15, 2016

In light of National Canine Cancer Awareness month, I wanted to try to answer a question that many dog owners have— “How can I tell if my dog has cancer?” Unfortunately, I cannot write an article about “3 Easy Steps on How to Know if My Dog Has Cancer.” That doesn’t even exist! What I can tell you is how to improve early detection.   

What Does Cancer Look Like?

Cancer comes in all shapes, sizes, locations and does not discriminate with regard to age and breed. One in four dogs will develop cancer in its lifetime making it the number one cause of disease-related death in dogs. Research has shown that early detection is the best method, and one of the only methods in our control, for determining a promising cancer prognosis. Unfortunately, not all cancers are easy to detect.

In an attempt to help dog owners identify cancer in its earliest stages, I’ve broken cancer down into four very broad, very non-scientific categories. Those four categories are: 1) external cancer, 2) internal cancers, 3) bone cancers and 4) blood cancers.

External Cancer

An external cancer will often be referred to as a “lump”, “mass” or “tumor”. Tumor is what most people think of when they think of cancer. However, the word “tumor” does not necessarily mean cancer. A tumor is defined as “a swelling of a part of the body, generally without inflammation, caused by an abnormal growth of tissue, whether benign or malignant.” Note the words benign (non-cancerous) or malignant (cancerous) can apply to the word tumor. In fact, all four of the above terms can be used interchangeably. For example, a mass can be malignant and a tumor can be benign. Therefore, don’t panic if your veterinarian uses one of these terms over another! 

What to Look For:

External masses can come in every shape, size, color and location. Size isn’t always a good indicator of seriousness. Small masses can have a poor prognosis and larger masses can have a good prognosis. It’s almost impossible to look at a mass and definitively tell whether it is malignant or not.

Whenever you notice a new growth, lump or bump on your dog, or you notice that one is changing, you should bring it to your veterinarian’s attention. They will be able to examine it and possibly do some simple tests to tell you if it warrants concern.  

Luckily, the best way to identify a new mass and monitor an existing mass is by petting, grooming and bathing your dog! Not too bad, right? Be sure to feel all over their body—their legs, toes, ears, neck, tail and if possible, their mouth. It’s good to get in the habit of examining your dog like this on a regular basis so you know if anything is new or changing.

Internal Cancer

This one is a tough one. Obviously, we can’t see inside our dogs and they can’t tell us how they’re feeling.  How do you know what’s going on in there? An internal cancer, is mass or tumor that is inside the body. That could be organs like the liver, spleen, kidneys, heart, stomach, lungs, and so on.

What to look for:

My best recommendations is to keep up with your dog’s annual wellness exam, especially as your dog ages. They will perform a thorough physical exam and may run annual bloodwork that will check organ function and blood counts. Abnormalities on the lab work could alert you to an underlying issue that needs further workup.

A few things you can monitor at home are your dog’s:

  • Food and Water Intake- Too much? Too little? 
  • Bathroom Habits- Is he needing to go outside more? Less? Are his bowel movements normal?
  • Attitude- Does he seem to be depressed? Laying around a lot? Hiding?
  • Behavior- Has he lost interest in normal activities? Changes in routine?
  • Pain or Discomfort-Is he whining? Is he painful to the touch? Limping? 
  • Vitals- Is he breathing heavier? Shallower? Panting?

Go with your gut. You know your dog the best so any abnormal or concerning behaviors can warrant a quick trip to the vet.

Blood Cancer

Blood cancers are another challenging one to identify since, again, they are not visible. Most people know leukemia and lymphoma can occur people but did not realize dogs can get leukemia and lymphoma as well. Both, leukemia and lymphoma, are cancers of the blood-stream and/or lymphatic system.

What to look for:

The best way to detect these types of cancer are similar to the above. Examine your dog frequently feeling for swollen lymph nodes typically around the neck and the back of the hind legs. Swollen lymph nodes can often feel like a mass when very large. Also, take note of any unusual skin lesions, as bruising can be a sign that certain cells in the bone marrow are low. These cancers can also be detected on lab work. Keeping up with annual vet visits and blood work can help detect these types of cancer. Though most often not outwardly visible, these cancers can make your dog not feel well so similarly to above, monitor your dog for abnormal behavior or changes in habit.

Bone Cancer

And finally, bone cancer. Bone cancer is more common in large and giant breed dogs than small breed dogs but it can affect any size of dog. The primary indication of bone cancer is pain or discomfort. Swelling can exist around the location of the cancer but sometimes no swelling is present at all. 

What to look for:

Bone cancers are often in the limbs and are accompanied by limping. They can also arise in other parts of the body like ribs, spine and skull where they would be painful to the touch and/or swollen. Bone cancer is a very painful disease and often progresses quickly so if your dog (especially elderly, large breed dog) suddenly begins limping or showing unexplained signs of pain, it is best to take your dog to the vet to get checked out. An x-ray is typically performed to look for changes in the bone caused by cancer and a sample of this area may be taken for a diagnosis.    


In short, I can’t give you a fool-proof way to guarantee your dog won’t get cancer; nor can I tell you about one test that will tell you if your dog has cancer. We all want our canine companions to be here with us as long as possible. My hope is that this very basic overview, educates dog owners on the different faces of canine cancer and, in turn, increases the chances of early detection.

Cancer coverage is included in AKC Pet Insurance’s base plan, CompanionCare. If you would like more information about our customizable plans, call 1-866-725-2747 and one of our Insurance Specialists would be happy to walk you through your coverage options.


The information provided in this blog is intended for educational purposes only and should not serve as a substitute for the professional medical advice of your veterinarian. Always consult your veterinarian with questions about your pet’s health and before initiating any treatment regimes. ​

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