8 Warning Signs of Cancer in Dogs: Is Your Dog at Risk?

Table of Contents 

  • Introduction
  • Most Common Types of Cancer in Dogs
  • Lymphoma
  • Melanoma 
  • Hemangiosarcoma
  • Osteosarcoma
  • Mast Cell Tumors
  • Warning Signs of Cancer in Dogs
  • Weight Changes
  • Collapsing
  • Mouth Changes
  • Coughing 
  • Changes in Bathroom Habits
  • Seizures
  • Nosebleeds
  • Skin Changes
  • Conclusion

Article at a Glance 

  • Cancer in dogs is more common than you think
  • Certain types of cancer are more common, including lymphoma and melanoma
  • Knowing the top warning signs of cancer will help you spot it before it’s too late 

Are you wondering if your dog is at risk for developing cancer? Cancer in dogs is a lot more common than many people realize. According to the American Veterinary Medical Association, around half of dogs over the age of 10 will develop cancer. Additionally, one in four dogs will develop neoplasia at some point in their life, which is an abnormal growth of tissues or cells in the body. While in many cases cancer can be life-threatening, if you catch it early enough, your dog may be able to recover. 

But how can you tell if your dog has cancer? Read this guide to learn about the most common warning signs of cancer in dogs. 

Most Common Types of Cancer in Dogs 

Before we dive into the warning signs of cancer, let’s take a minute to discuss the most common types of cancer in dogs. Cancer can take on many different forms, and it can affect different parts of the body, including tissues, bones, and blood. To provide the most appropriate treatment, an accurate diagnosis by a veterinarian is critical. 

Here are the most common types of cancer that dogs fall victim to:


According to the American Kennel Club Canine Health Foundation, lymphoma occurs two to five times as much in dogs as it does in people. Additionally, around 1 in 15 dogs will develop lymphoma in their lives. 

Lymphoma is a type of cancer that arises from the lymphocytes, which are white blood cells that fight disease. Normally, these white blood cells travel through the body into the blood stream and into lymph vessels, which interconnect the organs in the lymphoid system (lymph nodes, spleen, and thymus). In dogs, lymphoma typically appears as swollen lymph nodes in front of the shoulders, under the jaw, or behind the knees. Occasionally, this cancer will attack the chest or abdomens. Treatment will depend on the type of lymphoma, but most dogs respond well to chemotherapy. 

Golden retrievers are most likely to be affected by lymphoma. 


When most of us thin of melanoma, we think of skin cancer. However, melanoma is a type of oral cancer in dogs that most often occurs in canines with dark tongues and gums. 

The tumors are made of darkly pigmented cells, and they can be found anywhere on the body. Often, if you notice malignant melanoma in the oral cavity, it likely means that the cancer has already spread to other parts of the body. Unfortunately, if it has already spread to other parts of the body, it’s incurable. The most likely breeds to suffer from melanoma include chow chows, Doberman pinschers, standard and miniature schnauzers, and Scottish terriers. 


Hemangiosarcoma is a type of cancer that develops from blood vessel-lining cells. It typically attacks the spleen, but it can also attack the liver, skin, and heart. 

Dogs that suffer from this type of cancer rarely display any signs until a tumor ruptures and they go into shock. This will lead to extreme blood loss, sudden weakness, pale gums, and labored breathing. Emergency surgery is necessary to subdue the blood loss, and typically, this is followed by chemotherapy. Sadly, hemangiosarcoma rarely comes with any warning signs, so it can be difficult to spot. However, certain dog breeds are more susceptible than others. 

The breeds most likely to be affected by this cancer are golden retrievers, Portuguese water dogs, German shepherds, and Skye terriers. 


This type of cancer is the most common bone cancer in dogs. It tends to attack long bones, but it can attack any bone in the body. 

Osteosarcoma progresses rapidly, spreading to the lymph nodes, lungs, and other bones. Lameness, swelling, and pain in the affected limb are all common warning signs of osteosarcoma in dogs. Since it’s such an aggressive, rapidly spreading disease, amputation is often the recommended treatment. Mastiffs, great danes, and Irish wolfhounds are most likely to be affected by osteosarcoma. 

Mast Cell Tumors 

Mast cell tumors tend to form on the skin, and they can vary from being relatively benign to aggressive. Once formed, they often spread to other parts of the body. 

Mast cells are immune cells that are responsible for allergies. In addition to forming on the skin, they can be found in all types of body tissue. Dogs most likely to suffer from mast cell tumors include boxers and bulldogs. 

Warning Signs of Cancer in Dogs 

Now that you know about some of the most common types of cancer in dogs, let’s talk about the warning signs you need to watch for. These include:

1. Weight Changes 

If your dog is suddenly losing weight without any explanation, there’s a chance that they’ve developed cancer. Often, weight loss is a sign of a gastrointestinal tumor. Cancer can cause your dog to lose weight while maintaining its current appetite, making it all the more difficult to spot. Whether your dog is shedding pounds rapidly or slowly, you should make an appointment with your vet. On the flip side, sudden weight gain may also be a sign that your dog has cancer. If you notice that your dog is bulking up or has a sudden appetite spike, it’s time to take them to the vet. 

2. Collapsing 

If your dog suddenly starts collapsing on the floor, take it to the vet immediately. Collapsing, weakness, and general lethargy are all common signs that your dog might be suffering from cancer. 

Often, this will happen in large dog breeds. 

3. Mouth Changes 

If you notice that your dog is suffering from mouth sores, bad breath, lumps, bleeding, or changes in gum color, then cancer may be the culprit. Dog owners often forget to examine their pets’ mouths, so make sure you’re on the lookout for these signs whenever you brush your pet’s teeth. 

You can also check for mouth changes when your dog is yawning or eating. 

4. Coughing 

Coughing is another common sign of cancer in dogs. However, coughing can be a sign of any number of illnesses and issues, so if you hear your dog cough, you shouldn’t automatically jump to cancer. 

For example, small breeds of dogs tend to develop coughs when they have issues in their windpipes. If your dog just coughs once or twice, there’s no need to sound the alarm bells. However, if your dog continues to cough for a few days or more, it’s time to talk to your vet. 

5. Changes in Bathroom Habits

Every dog experiences diarrhea from time to time, and it generally isn’t a cause for major concern. However, if you notice that your dog’s diarrhea persists or gets worse, then it’s time to see the vet. 

Additionally, if your dog is constantly begging to go outside to use the bathroom, experiences difficulty peeing or having bowel movements, or there’s vomit or blood in their urine, then there’s a chance that cancer might be the issue. 

6. Seizures

Seeing a dog have a seizure can be very scary. A seizure is often a sign of a brain tumor, which are more common in older dogs. If you notice your dog having sudden and uncontrolled bursts of activity, such as jerking legs, champing, chewing, or foaming at the mouth, then they may be suffering from a seizure. 

7. Nosebleeds

While humans occasionally suffer from nosebleeds, a nosebleed in a dog is never normal. Nosebleeds in older dogs are particularly concerning, as it may be a sign of nose cancer. If your younger dog has a nosebleed, there may be a foreign object stuck in their nose. Discharge from the nose is also a concern, as this may be a sign of a facial tumor. 

8. Skin Changes 

Skin changes in your dog may also indicate cancer. Lumps, bumps, and other changes in the skin should always be checked, and the only way to distinguish from a lump that’s benign or malignant is to go to your vet for a sample. 

Warning Signs of Cancer: Wrap Up 

We know it’s never fun to think about your dog having cancer. Sadly, dog cancer is a fact of life, and knowing the above warning signs may help you catch the cancer early, and you might have a better chance of treating it. 

If you’re wondering if your dog is suffering from cancer-related pain, check out this guide to learn about the top signs of pain in dogs

Written by Mead Johnston

Mead is an experienced dog trainer, writer, and lover of animals. She has always been surrounded by animals and had a passion for learning more about them every day. This passion grew tremendously when Mead brought home a Great Pyrenees x Golden Retriever named Mac in 2018. Mead has continued to learn more about dogs whenever possible and wherever possible, while also helping so many wonderful clients. Her goal is help her clients and their dogs become confident in their daily lives. As a dog trainer, she often helps clients who are starting off with a puppy or they might have an older dog that is presenting challenging behaviours. Mead believes in the all-natural uses of Pet CBD to help our furry loved ones live longer, happier and healthier lives.

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