Cancer in dogs: symptoms and treatment

Mar 11, 2022

It’s the diagnosis we never want to hear: cancer. Cancer in dogs is a leading cause of death, typically affecting 1 in 3. Selective breeding puts some purebred dogs at greater risk than mixed breeds for specific kinds of cancer in dogs. 

But the good news is that medicine has made tremendous strides in treating dog cancer. Working closely with your vet, dogs with cancer have more of a fighting chance than ever before.

Common signs of cancer in dogs

First, understand that dogs can experience many kinds of cancer. The warning signs vary, depending upon the type of cancer your dog might have. The most common symptoms include:

Lumps and bumps

Some superficial skin bumps are sebaceous cysts, which are basically a clogged oil gland. These are generally harmless. The same is true for lipomas, which are soft, benign fatty masses under the skin. These are common in older dogs. Large lipomas may inhibit your dog’s movement, in which case your vet may recommend removing them surgically.  Dogs also get warts, infected hair follicles, and hematomas (blood blisters). Airvet is always available to discuss these findings with you, but remember that the only way to obtain a conclusive diagnosis is to bring your dog to a vet for an examination and tissue sample.

One of the most common canine masses is a mammary gland tumor. This cancer usually begins as one or more nodules in the nipple area, which may become inflamed and swollen. Malignant mammary tumors tend to spread to nearby lymph nodes if left untreated. Unspayed female dogs and those who were spayed after their first heat cycle are at the highest risk for a mammary gland tumor. Toy and miniature Poodles, Spaniels and German Shepherds are also at higher risk for mammary tumors than most other breeds. While both female and male dogs of any age and breed may develop this type of cancer, mammary tumors in male dogs are rare. 


Chronic lameness can be a sign that your dog has a cancer called osteosarcoma, a type of bone cancer. Osteosarcoma most often affects the long bones of the dog’s body. Large dogs and giant breeds are especially prone to this cancer. Your dog may walk with a persistent limp and the affected limb may be swollen, signaling pain. If you observe any of these symptoms, schedule an appointment with your vet promptly. Bone cancer grows quickly, and can spread to the lymph nodes and lungs.

Pigmented masses

Pigmented masses sometimes signal a malignant melanoma, a type of skin cancer in dogs. Melanomas in all dog breeds frequently appear around the mouth, nail beds, footpads and eyes. This dog cancer comes from the body’s pigment-producing cells. Some breeds with dark-colored oral tissues, such as the tongue of the Chow Chow, may be especially vulnerable to this cancer. 

Swollen lymph nodes

Swollen lymph nodes may signal lymphoma, a common malignant cancer that accounts for up to 20% of all canine cancer diagnoses. Swollen nodes in the neck, knee and armpit are typically where you’ll notice the first evidence of lymphoma. This cancer affects the lymphocyte, a type of white blood cell that plays an important role in immune function. Lymphoma can also affect various organs and bone marrow.  Golden Retrievers and Boxers are especially prone to lymphoma.

Other cancers such as melanoma, osteosarcoma, and mammary gland tumors can spread to nearby lymph nodes. When this happens, one or more lymph nodes in an area of the body may be enlarged.

Mast cell tumors

Mast cell tumors are a very common type of skin tumor in dogs. The mast cell is an immune cell involved in the body’s allergic and inflammatory response by producing histamine. Tumors of this kind can be found anywhere on or under the skin and may grow slowly or rapidly. Sometimes the mass will appear as a wound that won’t heal. Sudden trauma to a mast cell tumor can cause a large release of histamine, which can trigger vomiting, diarrhea, or even shock.

When a mast cell tumor is found, removal is often recommended. The mass is sent to a pathologist for grading. This is important, since lower grade mast cell tumors tend to just invade tissues locally, whereas high grade tumors tend to spread throughout the body. 


This aggressive cancer most frequently targets the blood vessels in the heart, spleen, liver or skin, and is most commonly found in German Shepherds, Golden Retrievers and other large breeds. Sometimes this type of cancer is difficult to detect until a large tumor is present or a vessel ruptures. Unfortunately, a common consequence of this type of cancer is sudden collapse when a mass in the abdomen ruptures. The dog is unable to stand and may have pale gums; this is always an emergency situation.

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Other symptoms that could signal cancer

Other signs of cancer can overlap with other common ailments. Sudden weakness or collapse, chronic vomiting, diarrhea, labored breathing or coughing, and unexplained weight loss should be taken seriously. These symptoms could indicate a variety of issues, including, but not limited to cancer. If your dog is experiencing any of the following, seek the advice of a veterinarian that can help determine the cause.

Treating cancer in your dog

Before prescribing a specific treatment for dog cancer, diagnostic tests including sampling any masses, X-rays, blood work, ultrasound, and other advanced imaging may be needed. With many types of cancer, it is important to try to determine whether it has already spread to other parts of the body and not simply focus on what is visible. Sometimes, it’s necessary to obtain a referral to a veterinary oncologist for some of these diagnostics and dog cancer treatment options.

The course of your dog’s cancer treatment will be decided by your veterinary team based on your dog’s specific condition and prognosis. Discuss all of the options with your vet, and what to expect. Some types of cancer in dogs require surgical removal of a mass, radiation, and/or chemotherapy. You should anticipate a continuing course of at-home care, and possibly many follow up visits depending on the therapy required. Sometimes, a cure is possible; sometimes remission is the goal.

Recovering from cancer treatment

As your dog recovers from cancer treatment, nutrition takes on special importance. A balanced, digestible diet will make recovery more comfortable. Sometimes specific diets are prescribed as part of cancer therapy.

When treating dog cancer is not an option

If your dog’s cancer prognosis is poor or if cancer treatment is not an option, there might be palliative care options that your veterinarian recommends to try to keep your dog comfortable for as long as possible. Palliative options won’t stop the progression of the disease, but can reduce stress and pain so that you and your dog have more good days together. You can explore these options with your veterinarian or consult with Airvet.