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From their goofy grins to their silly head tilts when we talk to them, dogs are, quite frankly, the best. As veterinarians, we know that dogs hold a special place in our clients' hearts, which is why canine cancer is certainly a topic we hope to avoid having to discuss. The unfortunate truth is that cancer in dogs is so prevalent that, according to the Veterinary Cancer Society via this AAHA article, 1 in 4 dogs will develop cancer at some point. Nearly 50 percent of dogs over 10 years old will develop cancer. On a positive note, the same AAHA article points out that half of all canine cancers are treatable if caught early on, as new treatments are being researched and developed on a near-continuous loop. It helps to be aware of the causes, signs, and other facts about dog cancer, so we've rounded up essential facts on the topic and shared them below.

Types of Dog Cancer

There are various types of dog cancer, so it helps to be aware of these signs, symptoms, and how they come to be. The most common cancer types in dogs are:

Mast Cell Tumors

Mast cell tumors are a form of skin cancer. Mast cells reside in the connective tissues, especially the vessels and nerves that are close to the external surface of your dog (skin, lungs, nose, and mouth). Mast cell tumors are graded according to their skin location, presence of inflammation, and how well they are differentiated.

Typically seen in Bulldogs, Boxers


Melanoma is a common type of cancer in dogs and is the most common malignant tumor of a dog’s mouth. Skin tumors are among the most common tumors found in dogs, and many are benign. Oral melanomas are more likely to be malignant.

Typically seen in Dobermans, Schnauzers, Chow Chows


Lymphoma is a cancer of a type of blood cell (lymphocytes) and lymphoid tissues that accounts for 20 percent of all canine cancers. Lymphoid tissue is normally present in many places in the body, including lymph nodes, spleen, liver, gastrointestinal tract, and bone marrow. Lymphoma appears most often as swollen lymph nodes under the jaw, in front of the shoulders, or behind the knees.

Typically seen in Golden retrievers

Bone Cancer (Osteosarcoma)

Osteosarcoma refers to the most common bone tumor found in dogs.

Signs of bone cancer in dogs are as follow:

  • Lameness
  • Pain
  • A firm swelling at the site of the tumor

Bone cancer can affect any breed of dog, but it is more commonly found in giant and large breeds.

Typically seen in Great Danes, Mastiffs, Greyhounds


Hemangiosarcoma is a highly malignant cancer that can spread rapidly, causing tumors almost anywhere in the body. It is most often found in the dog’s heart and spleen and is usually in the advanced stage before it is diagnosed.

Typically seen in German Shepherds, Golden Retrievers

Mammary Gland Carcinomas

Mammary gland carcinomas are the most common tumors in unspayed female dogs, but they are often overlooked since they usually appear small nodules around the nipple. Unfortunately, the nodule may quickly grow into a large, painful tumor that can ulcerate and become an open wound. Approximately 50 percent of these tumors are malignant, but they can be cured with surgical removal if the cancer has not metastasized. Fifty percent of malignant masses will be fatal. Spaying a dog before her first heat cycle significantly decreases the mammary cancer risk.

Are certain breeds more or less disposed to cancer?

Several different types of cancers can affect dogs. Genetics have been shown to correlate with an increased risk of certain cancers. Unfortunately, no one knows exactly why this is. Some of the most common and most loveable breeds top the list, including Golden Retrievers, Labrador Retrievers, German Shepherds, and Boxers. Even mixed breed dogs are not immune to cancer.

There appear to be fewer small breeds of dogs diagnosed with cancer compared to large breeds. However, approximately 1 in 4 dogs will, at some stage in their life, develop neoplasia. Almost half of dogs over the age of 10 will develop cancer. Older, unspayed females of every breed are most commonly affected.

What is the main cause of cancer in dogs?

There is no one cause of dog cancer that is known. Genetics and environmental contributors such as second-hand smoke have been implicated in cancer risks in dogs.

Does my dog's lifestyle factor into getting cancer?

Intact males, particularly cryptorchid males, are at risk for testicular cancer. Intact females are at greater risk for mammary cancer, but spaying before the first heat cycle significantly reduces this risk. Obesity has been linked with some cancers, so keeping your pet at a lean body condition can be a preventative measure for cancer. Preventing obesity has also been shown to improve other illnesses in dogs that can decrease their life expectancy.

Is cancer in dogs preventable?

Unfortunately, the cause of most cancers is unknown. However, spaying/neutering pets and keeping your pet in a lean body condition can reduce risk. Early detection and treatment are the best ways to manage cancer in pets. 

Possible signs of dog cancer are as follows:

  • Sudden weight loss
  • Difficulty eating/breathing
  • Visible mass or lump
  • Unexplained lameness or swelling
  • Abdominal enlargement
  • Persistent vomiting
  • Diarrhea
  • Poor appetite

Is cancer in dogs treatable?

Whether dog cancer is treatable depends on the tumor type, location, and characteristics of the tumor (malignancy). Different treatment options range from surgical removal, chemotherapy, and radiation, to name the most common. Current research includes immunological treatments to help the dog’s own immune system treat the cancer.