Cancer in Dogs Explained: Signs, Causes, and Most Common Cancer Types

What Happens When a Dog Gets Cancer?

When a dog gets cancer, the warning signs are similar to those in people and often include physical changes like bumps that don’t go away, injuries that don’t heal, swellings, enlarged lymph nodes, bleeding, weight gain, or weight loss. 

Dogs get cancer at similar rates as humans. While dogs at any age can get cancer, the risk is higher in older dogs. Once again, same as in people. 

If your dog is exhibiting these warning signs or changes to its typical behaviors of eating, drinking, exercising, urinating, defecating, and sleeping, a visit to the vet is warranted.  

What’s the Most Common Cancer in Dogs?

The most common type of cancer in pet dogs are:

• Melanoma or skin cancer
• Osteosarcoma or bone cancer
• Lung Cancer
• Mast cell tumors 
• Lymphoma
• Hemangiosarcoma
• Mammary cancer or breast cancer.

The type of cancer can depend on the dog breed as well as behaviors such as sun-bathing or heat cycles in intact female dogs.     

In general, the types of cancers can be separated into categories such as carcinomas and sarcomas.     

Carcinomas are a common type of dog cancer that starts in the skin cells and tissue-lining cells. Common examples are bladder cancer and mammary cancer. 

On the other hand, a sarcoma is a tumor type that starts in soft tissues like blood vessels and muscles or hard tissues like bones. Examples are hemangiosarcoma and osteosarcoma. 

Types of Cancer in Dogs

Skin Cancer in Dogs. There are different types of canine skin cancers. The most common include malignant melanoma, squamous cell carcinoma, and mast cell tumors.

Bone Cancer in Dogs. Osteosarcoma is the most common bone tumor or dog cancer. It affects dogs of all ages and usually develops on the limbs.

Liver Cancer in Dogs. Liver cancer in canines is a tumor growing on the liver. The medical term for liver cancer is hepatocellular carcinoma.

Breast Cancer in Dogs. Also known as mammary tumors affect male and female dogs. 1 in 4 intact female dogs will develop breast cancer at some point. 

Bladder Cancer in Dogs. Invasive transitional cell carcinoma (TCC) is the most common type of bladder cancer. It stems from the bladder’s epithelial lining and muscles. 

Spleen Cancer in Dogs. In dogs, the most common spleen cancer is hemangiosarcoma. The tumor develops from the cells that line up blood vessels in the spleen. 

Lung Cancer in Dogs. Lung tumors are rare in dogs as primary cancer and usually appear in the form of metastasis – they spread to the lungs from cancers in other parts of the body. 

Prostate Cancer in Dogs. Prostate cancer in canines has two forms – prostatic adenocarcinoma and prostatic urothelial cell carcinoma. They are aggressive and metastasize quickly.  

Mouth Cancer in Dogs. Canine mouth cancer takes several forms – malignant melanomas, squamous cell carcinomas, and fibrosarcoma. 

Stomach Cancer in Dogs. Stomach or gastric tumors are diverse and occur like lymphomas, muscle tumors, fibrosarcoma, adenocarcinomas, mast cell tumors, etc. 

Testicular Cancer in Dogs. Testicular tumors in dogs are typically malignant, meaning they have the potential to spread to other parts of the body.

Anal Gland Cancer in Dogs. Anal gland tumors are also usually malignant and, due to their location, are typically found when they are at a more advanced stage. 

Thyroid Cancer in Dogs. Thyroid gland tumors are rare in dogs and usually benign. They generally develop in older dogs and can be easily felt during a physical exam.

Lymphoma Cancer in Dogs. Lymphoma is common cancer found in dogs that usually starts in the lymph nodes. Canine lymphoma takes several different forms. 

Pancreatic Cancer in Dogs. Pancreatic cancer in canines is rare. However, if it develops, it is most likely malignant. Insulinoma and adenocarcinoma have the highest incidence.  

Nasal Cancer in Dogs. Nasal tumors are uncommon in dogs and have a low metastatic rate but can cause breathing issues and deteriorate the dog’s quality of life. 

Colon Cancer in Dogs. Colon cancer in pets is less common than in people. As a form of intestinal cancer, canine colon tumors can be malignant or benign.

Intestinal Cancer in Dogs. The three types of intestinal tumors in dogs are leiomyosarcoma (usually on the small intestine), lymphoma, and adenocarcinoma (on the large intestine).  

Kidney Cancer in Dogs. Kidney cancer or renal cancer affects the kidneys. Kidney cancer in canines tends to spread to other parts of the body.

Brain Cancer in Dogs. Brain tumors can occur at any age but are difficult to diagnose. Every dog older than 5 years and with seizures need to be evaluated for brain cancer. 

Eye Cancer in Dogs. The most commonly diagnosed eye tumor in dogs is uveal melanoma. They usually arise from the ciliary body and iris. 

What are the Signs of Cancer in a Dog?

The signs of canine cancer vary from something as unspecific as appetite changes to something as unique as visible lumps or growths. Here is a list of the signs of dog cancer:

• Weight loss or gain 
• Loss of appetite
• Difficulty swallowing
• Lameness
• Tumor growth on parts of the body 
• Skin pigment changes
• Abnormal odor from body openings
• Heavy breathing and coughing 
• Increased thirst, drinking, and urination 
• Non-healing wounds or sores 
• Low energy levels 
• Evidence of pain. 

It is important for pet owners to take their pets for a physical exam every year as exams can lead to early detection. Treatment options can be less aggressive if cancer is caught early. 

What Causes Cancer in Dogs?

Canine cancer is a multifactorial condition. Common causes of dog cancer are:

• Hormones. Hormones released during heat cycles in intact female dogs are predisposing factors for mammary gland tumors. The hormonal effect on cancer is less pronounced in male dogs. 
• Exposure to chemicals. Long-term or continuous exposure to certain chemicals (tobacco smoke, asbestos, waste incinerators, pesticides) increase the risk of developing specific types of cancer. 
• Ultraviolet sun radiation. Dogs with lighter, shorter coats who lounge in the sun for extended periods of time are more susceptible to hemangiosarcomas and melanoma or skin cancer. 
• Genetics. Some dog breeds are genetically prone to cancer types. For example, the incidence of bone cancer is higher in breed dogs like German Shepherds and Golden Retrievers. 

How does Cancer in Dogs Spread? 

Canine cancer can spread through the blood or lymph systems or by a direct spreading of the cancer cells from a nearby location in the body. 

Not all cancers spread or go through metastasis. Usually, malignant cancers tend to spread more. Malignancy can be evaluated by performing a chest x-ray as the lungs are typically where cancers spread first. 

How is Cancer in Dogs Diagnosed?

Dog cancer is diagnosed by a veterinarian performing a thorough physical examination and diagnostic tests such as blood work, fine needle aspirate, ultrasound, and x-rays. 

Depending on the form of cancer suspected, the primary veterinarian may refer the dog to a veterinary oncologist for further testing such as biopsy or MRI.

Some cancers are more difficult to diagnose because they are not visible during a physical exam, such as brain tumors. On the other hand, others can be suspected with just a simple physical exam. 

What are the Treatments for Cancer in Dogs?

The treatment options for cancer in dogs include surgery, chemotherapy, immunotherapy, and radiation therapy. Cancer in dogs treatment varies depending on the form of cancer (malignancy and progression). 

A dog with a tumor may have surgery as cancer treatment, whereas a dog in advanced stages of a tumor may need surgery as well as radiation therapy. 

New cancer treatments are developed every day, including bone marrow transplants and injections like Stelfonta, which treats mast cell tumors in dogs. Stelfonta was approved by the Food and Drug Administration in 2020. 

Clinical trials of new drugs created to treat cancer in dogs are constantly underway and being evaluated by the FDA. 

How Long Will a Dog Live After Being Diagnosed With Cancer?

The lifespan for a dog with cancer can vary depending on the form of cancer and cancer treatment. 

While some dogs can be cured and have a normal quality of life, for others, the prognosis is poor, and euthanasia remains the only humane option. 

As a pet owner, the most important thing you can do for your dog is providing adequate and ongoing veterinary care. 

So, if you are wondering how to prevent cancer in dogs, make sure your pet’s needs (diet, exercise) are met and practice regular veterinary checkups.