Six Common Types of Cancer in Dogs

Pet Health and Safety  •  Pam Karkow  •  Tuesday, October 5, 2021

It’s the diagnosis all pet parents fear. Cancer. The disease will affect one in three dogs at some point in their life, but if caught early, roughly half of canine cancers are treatable. The month of November is Pet Cancer Awareness Month, so this is a good time to be reminded of some of the most common types of pet cancers, and the signs and symptoms that come along with them.

Mammary Gland Tumors

This type of tumor usually begins as one or more nodules around the nipples and presents itself as a swollen and inflamed area. Malignant tumors can spread to lymph nodes and mammary glands if left untreated. Mammary gland cancer primarily affects female dogs that aren’t spayed as well as those spayed after 2 years of age.


This is the most common bone cancer in dogs. It can affect any bone and spread quickly, especially to lymph nodes and the lungs. It is usually detected after it has spread, due to its aggressive nature. A dog with osteosarcoma may limp and the affected limb may appear swollen. This type of cancer affects large and giant dog breeds the most.


Melanoma’s are cancer of the pigment-producing cells. This cancer can affect a dog’s mouth, lips, nail beds, footpads, and eyes. Symptoms are dependent upon the location of cancer and can include swelling at the site, discharge from the eyes, and sores in the mouth. Melanoma affects breeds with darkly pigmented oral tissues.

Mast Cell Tumors

Mast cells are immune cells involved in allergic and inflammatory reactions. A mast cell tumor usually presents itself as a skin lesion that will not resolve. Mast cells are located throughout the body, but tumors concentrate in vessels and nerves near the skin, mouth, and nose. The area around the tumor may become irritated due to the uncontrolled release of histamine from abnormal growth of the cells.


A common malignant tumor that accounts for up to 20% of all canine tumor cases, lymphoma affects the white blood cells that play an important part in immune function. The good news is that lymphoma in dogs is highly treatable. Symptoms include swollen lymph nodes in the neck, knee, and armpits. Lymphoma can affect all breeds. 


A rapidly spreading form of cancer, hemangiosarcoma is a cancer of the cells lining the blood vessels that frequently targets the heart, skin, spleen, and liver. Dogs with hemangiosarcoma may act weak, but often show no signs. Unfortunately, one of the first signs of this type of cancer is sudden collapse, usually due to massive internal bleeding from a ruptured spleen.

Early Detection is Key

Not all bumps and lumps are cause for concern, and there’s no reason to panic if your dog has some of the symptoms above. Many conditions cause similar clinical signs, and signs vary depending on the type of cancer. If your dog has a lump or bump that seems new, it is a good idea to have it checked out. Some tumors are nothing to worry about--they’re just lipomas, benign fatty tumors that are just another fun part of your dog getting older. It is not uncommon for an elderly dog to have several soft movable lumps under their skin. But if the bump is hard or does not move, make an appointment as soon as possible. As the saying goes, better to be safe than sorry, and early detection greatly increases the chances for successful treatment.

Let Pet Insurance Help

Pet insurance can help ensure you’re able to give your pup the best treatment possible if he’s diagnosed with cancer. PetPartners offers cancer coverage included in their accident and illness base plan. Get a quote today.

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