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What are Signs of Cancer in Dogs?

a brown lab looking straight at the camer standing in a field

Have you just received a cancer diagnosis in your dog, or have you just found a new lump or bump on your dog? You may think your dog has cancer and looking for more information on the signs of cancer. There are certain signs that you can look for that may mean that your dog has cancer, but many of these signs can mean that there is something else going on with your pet. This article will explain all about cancer and the common signs that you need to watch out for in your furry friend. 

What is cancer?

Cancer is when normal cells grow out of control and invade surrounding tissue.   Metastasis is the medical term for the spread of cancer to other areas in your pet's body. Cancer can be localized to just one area or organ in the body or can be generalized and spread throughout your dog's body. If it is just in one area, it is usually a better outcome than if cancer has spread all throughout your dog's body.

The cause of cancer is usually unknown. Genetics can play an effect on cancer in dogs. Also, some environmental factors do play a part in a dog getting cancer. Certain breeds such as Golden Retrievers and Boxers are more prone to cancer.

There are many different types of cancer that your dog can get. These are the most common types of cancers seen in dogs.  

  • Hemangiosarcoma
  • Lymphoma
  • Malignant Histiocytosis
  •  Mammary Cancer
  • Mast Cell Tumors
  •  Melanoma
  • Prostate Cancer

Signs of Cancer in dogs

There are many signs of in your dog that you can see that would indicate that they may have cancer. These are common signs of cancer seen in dogs

  • Abnormal, consistently growing swelling spots: If your dog has a lump, this is an obvious sign that your dog may have cancer. Not all lumps are malignant or cancerous; some lumps are benign, meaning not cancer. If you see lumps on your pet, your veterinarian can take a few cells from the mass, determine if this mass is cancerous or not.
  • Sores that will not heal: Dogs that get a cut or scrape that will not heal is a sign that this could be associated with cancer. Sometimes these sores will not heal because the infection present is resistant to the type of antibiotic that they are taking, but it can be a sign of cancer.
  • Weight loss: If your pet is losing weight, this could be a sign of cancer. Many times, when your dog has cancer, this will affect their appetite.   This is not the only reason that your dog may not be eating; numerous gastrointestinal diseases can also cause your dog not to want to eat.
  • Loss of appetite: If your pet is not wanting to eat, this could be a sign of cancer inside the intestinal tract. Some cancers can grow inside the intestines blocking food from passing through. This is not the only reason your dog may not be eating; numerous gastrointestinal diseases can also cause your dog not to want to eat.
  • Bleeding from any opening: If your dog has blood or an abnormal discharge from the nose, eyes, mouth, or penis/ vulva. This could be a sign of cancer. This could also be a sign of a serious infection. Your vet can look at your pet and help determine what is causing them to bleed.
  • Bad odor coming from the mouth: If you notice your pet has horrible smelling breath, this may be a sign of cancer. Most dogs will need a dental cleaning every few years. If you notice bad breathing, look for masses in their mouths, and scheduling them, dental cleanings will help make sure that everything is okay in their mouths. Your veterinarian can check out your dog’s mouth for any signs of cancer.
  • Difficulty eating: Dogs can get cancer almost anywhere. Masses can even grow in their mouths. It is a wonderful idea to give your dog a monthly exam to look for any new lumps and bumps. This way, if you do find a new lump, you can get your dog checked out sooner rather than later.
  • Lameness: If you notice your dog limping and has a swollen joint, this may be a sign of bone cancer. One of the most common signs of bone cancer is limping and a joint that is swollen.
  • Difficulty breathing:Certain types of cancers commonly spread to the lungs. This would cause your dog to have problems breathing. They may just be coughing every few days, but they may have problems breathing. If your dog is having problems breathing, this is an emergency and needs to be seen by a veterinarian right away.
  • Difficulty peeing or pooping: Your dog may be going to the bathroom more frequently or having accidents inside the house. If you notice this, they may have a urinary tract infection or have bladder cancer.  

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What to do if you see symptoms

If you see any of these signs or symptoms, it is best to see you, veterinarian, immediately. Your veterinarian will want to run bloodwork and do a full-body scan of your dog to look for cancer. IF they find a mass or lump, they may take a biopsy to check for any cancer cells. If you are worried about any lumps or swollen areas, show these to your vet and describe the signs and symptoms that you see in your dog.

Cancer can be a very sad diagnosis. There are many treatment methods that your veterinarian can discuss with you if your pet does have cancer. These signs are something that you can start to look for as your pet ages. The earlier you catch that your pet has cancer, the longer and happier life they can live. As soon as you notice any of these signs, make an appointment with your vet. They can help figure out if the signs that you see in your dog are due to cancer or something else.

Meet The Author 

Dr. Sara Ochoa DVM


Since she was a little girl, Dr. Ochoa knew that her dream was to become a veterinarian. With a tremendous passion and love for animals, she is now a great source of knowledge for others. Dr. Ochoa lives happily with her husband Greg and her babies: Ruby the Schnoodle and Bam-Bam the bunny.

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