7 Most Common Forms of Cancer in Dogs: What Pet Parents Should Look Out For

Can dogs get cancer? You might be surprised to learn that cancer is common in dogs — so common, in fact, that roughly 1 in 4 dogs will develop some cancer in their lifetime, with the risk increasing after 10 years of age.³  But some cancers are more common than others.

Read on to learn about the basics of canine cancer, what symptoms to look out for, and how common cancers are treated.

7 Common Cancers in Dogs

There are many different types of cancer in dogs, just like there are many different types of cancer in humans. Here are the top seven types of dog cancers, dog tumors, and neoplasia in dogs and what they look like.

1. Melanoma

Melanoma tumors are round masses, usually ¼ inch to 2 inches in diameter, and can be found anywhere on a dog’s body.⁴ Swollen lymph nodes are a main symptom. Generally, melanoma is treated by removing the tumor.

Early detection is key in treating melanoma tumors in dogs. Pet parents should regularly inspect their dog’s eyes, toes, and other areas of the body to spot unusual masses.

2. Osteosarcoma

Osteosarcoma is the most common type of bone cancer in dogs.⁵ Large breeds of dogs, like poodles, are very susceptible to bone cancers as they grow out of puppyhood. This kind of cancer can be very aggressive, spreading quickly throughout the body.  There are many side effects, but the biggest warning sign is sudden lameness. If this happens, take your dog to the veterinarian immediately for an X-ray or MRI.

3. Lung cancer

Common in senior dogs, lung cancer usually requires surgery to correct because of how aggressive it can be. For example, adenocarcinoma of the lung is a fast-growing cancer that makes up 75% of all primary lung tumors in dogs.⁶ Watch out for ragged breathing and lethargy in your elderly dog. It may be a sign that their lungs are compromised.

4. Mast cell tumors

Mast cells (or basal tumors) are located in the connective tissues right under the skin. Mast cell tumors are prevalent, making up 20% of all skin tumors in dogs.⁷ Fortunately, this sort of cancer tends to be benign and easy to treat. If you find a potentially cancerous lump on your dog that is firm to the touch or clustered together, call your vet to schedule an appointment.

5. Lymphoma

Canine lymphoma is a cancer of lymphocytes (blood cells) and lymphoid tissues, similar to non-Hodgkin's lymphoma in people. The four main types of canine lymphoma are:

• Multicentric: The most common form of lymphoma and one that affects the entire body
• Alimentary: Fairly common, alimentary lymphoma affects the gastrointestinal tract
• Mediastinal: A very rare form of lymphoma that affects the chest
• Extranodal: A rare form that affects organs outside the lymphatic system (such as the kidney, lung, or eyes)

Symptoms differ according to each type. Vets can diagnose lymphoma through a fine-needle aspiration. Then, they will discuss the best form of chemotherapy to treat your dog’s cancer.

6. Mammary cancer

Mammary tumors affect female dogs, with rare occurrences in males. The American College of Veterinary Surgeons explains that mammary tumors are common in female dogs who were either not spayed until after 2 years of age, or never spayed at all.⁸ Poodles, dachshunds, and spaniels most commonly get this kind of dog tumor. Obesity at a young age can increase the risk of this cancer.⁸ Most mammary tumors are surgically removed and sometimes chemotherapy is recommended after the surgery.

7. Hemangiosarcoma

Hemangiosarcoma is an extremely dangerous and fast-moving cancer of the blood vessel walls that can cause cancerous tumors on dogs.⁹ The heart, spleen, and skin are the most affected areas, but hemangiosarcoma can be found anywhere in and on the dog’s body. It’s most common in golden retrievers, Labrador retrievers, and German shepherds.⁹  

Since this cancer often doesn’t receive a diagnosis until it’s very advanced, pet owners often make quick decisions regarding whether to do emergency surgery and remove the tumor. Sadly, the surgery can cause hemorrhaging during the diagnostic process. Many folks have to make the difficult choice to euthanize their pet.

Common Dog Cancer Terminology

Talking about cancer with your veterinarian can be overwhelming, and terminology may be difficult to process as you’re grappling with a difficult diagnosis. Some terms are used interchangeably, but when you are talking with your vet, it’s important to understand why they say what they say. The type of growth your dog has will affect how they’ll treat that particular cancer. There are three terms you should know when discussing this diagnosis: tumor, neoplasia, and cancer.³

1. Tumor: Sometimes called a “mass,” a tumor is the actual swelling of the physical appearance of the neoplasm that either be benign or malignant.³
2. Neoplasia: An uncontrolled growth of cells or tissues.³ Sometimes it forms a tumor that looks or feels like a firm bump. Other times, neoplasm isn’t firm to the touch. It tends to be benign and slow growing, and it rarely spreads throughout the body.
3. Cancer: A term used to describe malignant tumors and neoplasms that have metastasized — meaning they can spread while invading tissues around the cancerous tissue.

These terms aren’t exhaustive, but it’s enough to get you started so you can better understand your dog’s diagnosis.

Cancer Symptoms in Dogs

Cancer is tricky because the symptoms often look like other issues, like xylitol poisoning. However, it may be time to ask your vet to take a closer look if you see a combination of these signs:¹⁰

• Lethargy or lack of interest in playing
• Abnormal swelling
• Fever
• Loss of appetite or weight
• Difficulty eating or drinking
• Difficulty breathing
• Excessive vomiting or diarrhea
• Inflammation
• Bleeding from mouth, nose, or another body opening
• Bad odor from mouth
• Trouble during potty time
• Lumps, bumps, or discolored skin
• Mobility issues

This list doesn’t encompass every symptom, but it captures the most common among dog cancers so you can speak to your vet if your pup is experiencing any or all of them. Your vet can walk you through the specifics of the type of cancer your pet has after diagnostic testing.

Cancer Diagnosis

Once your vet narrows down the symptoms you’re witnessing at home, they will conduct tests. The tests will help them figure out if the tumor or neoplasm is cancerous and what kind of cancer your pet has. The diagnostics performed on your dog will include blood work, fecal samples, and a physical exam. Afterward, they will schedule a biopsy to collect tissue samples. Some may refer you to a veterinary radiologist for a CT scan, MRI, or other digital scans to identify where the cancer is.⁴

Dog Cancer Treatment Options

With the results from the tests in hand, your vet may recommend one or a combination of the following treatments:

• Chemotherapy: The chemotherapy may be localized with injections or intravenous.
• Radiation therapy: A vet uses controlled radiation to treat your dog’s cancer.
  
• Surgery: Certain cancers can be removed via surgery.
  
• Drugs: According to the FDA, there are three drugs approved to treat cancer in dogs: Palladia tablets (for mast cell tumors), Stelfonta injections (for mast cell tumors), and Tanovea-CA1 injections (for lymphoma). A fourth drug, Laverdia-CA1 (tablets), was conditionally approved to treat lymphoma in 2021.¹¹
  
• mmunotherapy: With this newer treatment, a vaccine created using your dog’s tumor cells is injected into your dog in an effort to trigger the dog’s own immune system to attack the cancer cells.¹²
  

Pet Insurance May Help the Cost of Cancer Care

A cancer diagnosis in the family upends your life. It’s especially heartbreaking when it’s your pet, who depends on you for care and comfort while they are ill. Treatment of all common cancers can be hard on your dog, not to mention very expensive for pet parents.

A dog insurance policy can cover all forms of cancer care, including experimental treatments.² With a policy on hand, pet parents can focus on caring for their ill pet with confidence that up to 100% of their veterinary bills may be reimbursed in as soon as 10 days. Consider getting a free quote from MetLife Pet Insurance, winner of the “Pet Insurance of the Year” Award in the 2023 Pet Independent Innovation Awards Program.¹ We are here to help!