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Cancer in Dogs: Facts, Symptoms and What to Expect


One of the worst things you can hear is that your dog has cancer. Despite the fact that survival odds have greatly improved over the last century for humans and animals, there are still many terrible symptoms and sometimes poor outcomes for certain cancers. 

Cancer is a terrible disease, for humans and for dogs. Many of us know a few things about human cancers, but which cancers are the most serious in dogs, and what is treatment like? And how do you know if your dog has cancer? 

What are some of the common types of cancer in dogs ?

There are so many different types of cancer that it is impossible to outline all of them in just one article. However, there are some cancers that are very common in dogs, and so it is important to know a little bit about each one.

Mast Cell tumors

The most common type of malignant skin tumor in dogs. Mast cells are a normal part of your dog’s response to allergens and release compounds like histamine during an allergic reaction. When tumors form from mast cells, they can rapidly affect other parts of the body like the liver, spleen, and bone marrow. Boxers, Labradors, and Boston Terriers are more susceptible to developing them.  


Malignant tumors that typically affect the long bones of the arms and legs. They can cause the bone to become so fragile that it fractures very easily, resulting in severe pain. Large breed dogs are more susceptible to these bony tumors. You can find more information on osteosarcomas in dogs here


Vascular tumors that can grow on the skin or can affect internal organs like the liver, spleen, and heart. When hemangiosarcomas occur internally, there is a high risk of bleeding if the tumor ruptures. This is especially dangerous with the spleen and liver because these can cause result in enough blood loss to become an emergency for your dog. Hemangiosarcomas around the heart can cause coughing, difficulty breathing, and eventually heart failure.  


A cancer that affects the lymph nodes, which are located throughout the body. It can start out in the lymph nodes of the gastrointestinal tract or in some of the peripheral lymph nodes located under the jaw, in front of the shoulders, or behind the hind limbs. Affected lymph nodes become enlarged, and it is very common for lymphoma to affect multiple lymph nodes. 

What are the signs of cancer in dogs? 

Cancer can sometimes be difficult to detect in the early stages. Some dogs act like nothing’s wrong at all while others may be a little slower than usual. Dogs that experience lethargy, vomiting, diarrhea, inappetence, and weight loss should see their veterinarian right away for a full physical examination. These clinical signs can occur in other illnesses, and so your vet may recommend diagnostic testing to help rule out other causes. Our article on weight loss in dogs helps outline some of these possible causes. 

Because cancers like lymphoma and hemangiosarcomas can spread to other parts of the body, your dog can have difficulty breathing if the cancer spreads to his lungs. In cases where a dog has a hemangiosarcoma on the liver or spleen, these tumors can suddenly bleed into the abdomen which causes acute abdominal pain, pale gums, and even collapsing. Respiratory distress and collapse are both medical emergencies that should be addressed immediately.   

Signs of cancer in dogs

General treatments for cancer in dogs 

There are many different ways to treat cancer in dogs, and there are certain factors that your veterinarian will need to take into consideration, including the type of cancer present, the stage, its location and size, and how far it has spread.


Surgery is implicated in cases with solitary tumors. When it comes to mass removal surgery, the biological nature of the mass must be considered. For example, if the tumor is small and benign (like some lipomas), then removing it may be relatively easy. However, if the tumor is malignant like a mast cell tumor, then wide tissue margins will need to be removed with the mass in order to ensure that all cancerous cells are removed. With osteosarcomas, this usually requires amputation of the entire affected limb due to the fast rate of cancer spread, aka metastasis. If there is a lung mass present, then your dog may need surgery to remove the affected lung lobe. Complete surgical margins can sometimes be difficult to achieve, and in areas where a tumor may be deemed as inoperable, treatments like chemotherapy and radiation are usually recommended. 

Chemotherapeutic Drugs

There are many different kinds of chemotherapeutic drugs, some of which are available in injectable or oral formulations. Treatment plans can involve one or several chemo medications in order to treat specific cancers. For example, patients with lymphoma are likely to have a combination of two or three chemotherapeutic agents prescribed to them. It is important to remember that chemotherapy drugs suppress the immune system, and so it may be easier for your dog to develop a simple infection. Often, it can be dangerous for pet owners to come into contact with their dog’s urine and feces because the chemo drugs are excreted from their dog’s body for roughly forty-eight hours. Owners must be sure to wear gloves and carefully dispose of their dog’s waste, and they must also watch their dogs for side effects. 

Radiation Therapy 

Radiation therapy is recommended for some cancers, especially those that are deemed inoperable. This is because oncologists can aim radiation directly at the cancer and can have few side effects for the patient. Radiation is also used in conjunction with certain cancers. For example, the gold standard of treatment for lymphoma is chemotherapy, but radiation can be directed at internal organs that are affected by generalized lymphoma. 

Choosing a cancer treatment for your dog 

These kinds of treatments might not be for everyone, especially due to cost, and some owners might choose to just focus on palliative care when it comes to their dog’s cancer. Depending on your dog’s cancer type and clinical signs, your veterinarian may prescribe gastroprotectants to help with vomiting and diarrhea, and she may also discuss using pain medications to help keep your dog comfortable. Steroids are commonly prescribed for lymphoma, lung disease, and other illnesses. Also, you will want to make sure that your dog is eating well and will want to keep track of his body weight. 

How long can dogs live with cancer? 

Trying to predict how long a dog will live with cancer is very difficult. The most important factor to increase your dog’s chances of surviving cancer is early detection. Cancer can be difficult to detect in dogs, especially in its early phases. Subtle clinical signs can occur and can mimic other illnesses, therefore early intervention is important. 

Make sure to check your dog for lumps and bumps on a regular basis, possibly once a week. Also, be sure to have any growths tested that are larger than one centimeter in diameter. If you suspect that your dog has a lump or bump, make sure to talk to your veterinarian about it. Remember that early intervention can make all the difference in your dog’s treatment!

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