Common Cancers in Dogs

As a pet owner, when you hear the word “cancer” you are devastated. In most cases, dog owners first suspect there is something wrong when they discover a lesion or growth on their pet or their pet begins to show signs of illness. Sometimes, however, cancer is diagnosed when it shows up on blood work or during a routine well-pet exam.

No matter how it is discovered, it is important to listen to your veterinarian and begin treatment immediately. If your dog is diagnosed with cancer, keep in mind that nearly one in three dogs will be diagnosed with some form of cancer in their lifetimes. It is not unusual and treatment options have advanced significantly in the last five to ten years.

Half of all cases of cancer in canines are treatable when caught early, according to the National Canine Cancer Foundation (NCCF). For this reason, it is crucial to understand what form of cancer your best friend has and how aggressive it is so you can explore the appropriate treatment options.


The most common form of cancer in canines is lymphoma, an overgrowth of cells in the bone marrow of lymph nodes. It is commonly found in dogs from six to nine years of age. It attacks the immune system of your pet and is a rapidly spreading form of cancer. If caught early, it is highly treatable. It is most often diagnosed after a pet parent has discovered swollen lymph nodes in the neck or a swelling behind the knees.


This is an intimidating name for cancer of the blood vessels. It usually affects the heart, liver or spleen but will travel to other organs. It can also occur just beneath the service of the skin. Unfortunately, there are seldom early warning signs of hemangiosarcoma, so it is rarely diagnosed until it is at an advanced stage.

Mast Cell Tumors

Mast cell tumors affect the skin, lungs and intestines and are quite common in mixed breeds and senior dogs. Mast cells transport enzymes and histamines that protect your dog’s body; when they proliferate, they turn against the immune system and attack it. Lesions on your dog’s skin are often the first sign of mast cell cancer and can cause discomfort.


This is a form of skin cancer that spreads rapidly and is very aggressive, although it is often benign. It often starts on the skin surface and grows inward to attack vital organs. It sometimes shows up as drainage from the eye, a swollen paw or pads or a lesion around the mouth. In many cases, benign tumors can be removed without any other treatment being necessary.


Bone cancer occurs most often in large breed dogs in their middle years. Osteosarcoma is usually malignant and it grows rapidly. Any bone can develop cancer, but it is most often in the legs. The earliest signs of osteosarcoma including swelling of the limbs and limping.

Mammary Cancer

Mammary cancer occurs in the mammary glands of female dogs. Dogs that have been spayed before they are two years old are much likely to develop this form of canine cancer. About half of all canine mammary tumors are malignant and have spread to other organs before they are diagnosed and can be removed. The first sign is usually a small bump near or on a dog’s nipple but can develop into a tumor that is painful and rapidly growing.

Breeds and Cancer

Any dog can develop cancer, with the odds increasing as the dog ages. There are also specific breeds that are more prone to cancer and tend to have shorter life spans because of the higher incidence of cancers. The breeds that most commonly develop cancer are:

  • Rottweiler
  • Bernese Mountain Dog
  • Bouvier des Flanders
  • German Shepherd
  • Great Dane
  • Doberman Pinscher
  • Labrador Retriever
  • Cocker Spaniel
  • Boxer
  • Golden Retriever

Any time you see a change in your dog, whether it is a lesion on the skin, a change in appetite or a change in mood, you should schedule an appointment with your veterinarian. It is always best to get the opinion of an expert and start treatment in the early stages of any illness, especially cancer. When caught and treated early, it can be a lifesaving decision.