Types of Cancer in Dogs

Cancer is one of the most serious health challenges dogs face today. In fact, about 1 in 4 dogs will develop cancer during their lifetime. For dogs over age 10, cancer is the leading cause of death. While these numbers are sobering, there is also hope—early detection, accurate diagnosis, and thoughtful treatment can greatly improve your dog’s quality of life and even extend it.

Whether you’ve just noticed a lump or your veterinarian has mentioned a possible diagnosis, understanding the types of canine cancer and what they mean is the first step toward informed, empowered care.

Common Types of Cancer in Dogs

Certain types of cancer are more frequently diagnosed in dogs and can vary by breed, age, and environment.

Most Frequently Diagnosed Cancers

Several cancers appear more commonly in dogs than others. According to the American Veterinary Medical Association (AVMA) and veterinary oncologists, the most frequent types include:

• Skin tumors, such as mast cell tumors, which make up nearly 20% of diagnosed cancers.

• Lymphoma, a cancer of the lymphatic system.

• Osteosarcoma, a painful bone cancer found mainly in larger breeds.

• Hemangiosarcoma, a fast-spreading cancer of the blood vessels.

Knowing which cancers are most common helps pet parents recognize early signs and seek help quickly.

What Increases a Dog’s Risk of Cancer?

Several factors may contribute to the development of cancer in dogs:

• Breed and genetics: Certain breeds are more prone to specific cancers. For example, Boxers are known to develop mast cell tumors, while Golden Retrievers have a higher risk of lymphoma.

• Age: Cancer is more common in older dogs.

• Environment: Exposure to pollution, secondhand smoke, lawn chemicals, or toxins can increase risk.

• Hormones: Some cancers are linked to reproductive hormones, which is why spaying or neutering may help reduce risk for certain types.

Skin and Soft Tissue Cancers

These cancers develop on or under the skin and are often the first to be noticed by pet parents.

Mast Cell Tumors

These are the most common skin tumors in dogs and can vary widely in appearance. They may shrink and swell and are often mistaken for insect bites. Breeds like Boxers, Bulldogs, and Boston Terriers are more susceptible. Early removal often results in a good outcome.

Melanoma

Melanomas often develop in the mouth, lips, or nail beds. While some are benign, others are aggressive and fast-spreading. Common in breeds like Cocker Spaniels and Schnauzers, early treatment is critical.

Lipomas and Sarcomas

Lipomas are soft, fatty tumors that are typically benign. Soft tissue sarcomas, on the other hand, may look similar but are more aggressive and can invade nearby tissues. Surgical removal is often the best approach.

Bone and Connective Tissue Cancers

These cancers typically cause pain and swelling in the limbs and may affect mobility.

Osteosarcoma

This is a highly aggressive bone cancer often seen in large and giant breeds like Rottweilers and Great Danes. It causes lameness and swelling. Treatment usually involves amputation followed by chemotherapy.

Chondrosarcoma

A cancer of cartilage, chondrosarcoma tends to grow more slowly and is less likely to spread than osteosarcoma. It often affects ribs, nasal passages, or limbs.

Fibrosarcoma

This cancer typically forms after trauma, inflammation, or previous injection sites. It's firm and can grow quickly. Surgery, often with radiation, is usually required.

Internal Organ Cancers

Cancers in the spleen, liver, and lymph system are harder to detect but can spread quickly.

Hemangiosarcoma

A cancer of blood vessel linings, hemangiosarcoma often strikes silently, typically in the spleen, liver, or heart. It’s often found after sudden collapse or internal bleeding. Unfortunately, it has a poor prognosis without early detection.

Lymphoma

Lymphoma affects lymph nodes and internal organs and is one of the most treatable dog cancers. Chemotherapy can often achieve remission, giving dogs more quality time with their families.

Internal Mast Cell Tumors

These may appear in the gastrointestinal tract, liver, or spleen, and can cause symptoms like vomiting, diarrhea, and weight loss. Treatment depends on tumor location and spread.

Cancers Affecting the Eyes and Toes

Though rare, cancers affecting the eyes or extremities can seriously impact a dog’s quality of life.

Squamous Cell Carcinoma

Often seen on sun-exposed areas like the nose, ears, and eyelids, this cancer appears as ulcers or crusty patches. Sunlight is a major risk factor. Early surgical removal is typically successful.

Eye Tumors

Though rare, ocular tumors can cause redness, swelling, or changes in eye color or size. Timely veterinary attention is crucial for diagnosis and treatment.

Physical Signs to Watch For

Dogs are masters at hiding pain and discomfort, which is why subtle changes often go unnoticed. But being attentive to even minor shifts in your dog’s body or behavior can be lifesaving.

• New lumps or bumps: Not all growths are cancerous, but any new lump should be checked by a vet. Pay attention to size, shape, texture, and whether it grows or changes.

• Sores that don’t heal: Persistent wounds may be a sign of skin cancer or another serious condition.

• Unexplained weight loss: If your dog is losing weight without a change in diet or exercise, it could indicate an internal tumor.

• Swollen lymph nodes: Especially in the neck, underarms, or behind the knees—these can be a sign of lymphoma.

• Bleeding or discharge: From the nose, mouth, ears, or rectum, particularly if it's ongoing or unexplained.

• Difficulty eating or swallowing: Oral tumors may interfere with normal chewing or cause pain.

• Limping or stiffness: Bone cancer like osteosarcoma often causes lameness or reluctance to move.

• Abdominal swelling: A swollen belly can indicate internal bleeding or tumor growth, especially in the spleen or liver.

Behavioral and Systemic Signs

Shifts in energy, appetite, or bathroom habits may also signal internal illness or cancer.

• Loss of appetite: If your dog suddenly doesn’t want to eat, even treats, take note.

• Lethargy or depression: If your once-lively dog is suddenly withdrawn or sleeping more than usual, it may be a sign something is wrong.

• Coughing or trouble breathing: This could indicate lung cancer or tumors pressing on airways.

• Changes in bathroom habits: Blood in urine or stool, difficulty urinating, or constipation can signal cancer in the digestive or urinary tract.

Perform Monthly At-Home Checks

Spend a few minutes once a month gently examining your dog from nose to tail. Feel for lumps, swelling, or unusual changes in skin texture. Look in their mouth and ears, check their eyes, and observe how they move and breathe.

Keep a Health Journal

Note any changes in your dog’s appetite, energy, weight, behavior, or physical appearance. Small changes may seem harmless but could be early red flags.

Don’t Delay Veterinary Visits

If something seems off, don’t take a “wait and see” approach. Trust your instincts and schedule a vet appointment. It’s better to rule something out early than to wait until the problem worsens.

Diagnostic Tools

Your vet may perform:

• Fine needle aspiration

• Biopsy

• X-rays, ultrasound, or MRI

These tests help determine the type, location, and stage of the cancer.

Treatment Options

• Surgery: Removes localized tumors

• Chemotherapy: Attacks cancer cells throughout the body

• Radiation therapy: Targets cancer in specific areas

• Immunotherapy: Boosts the immune system to fight cancer

Treatment plans are customized to your dog’s needs, age, overall health, and the cancer type.

Prognosis and Quality of Life

Every dog—and every diagnosis—is different. Some cancers respond well to treatment, while others may not. The earlier the cancer is detected, the better the chances for positive outcomes. Quality of life matters most. Palliative care, which focuses on comfort rather than cure, may be the best choice in advanced cases.

Prevention and Owner Tips

• Schedule regular veterinary checkups

• Examine your dog’s body weekly for lumps or swelling

• Feed a balanced diet with minimal chemical exposure

• Avoid cigarette smoke and lawn chemicals

• Stay informed, especially if your dog is a high-risk breed

Recognize the Early Signs

Cancer in dogs is a difficult but increasingly manageable diagnosis. The key is education, vigilance, and partnership with a trusted veterinarian. By recognizing early signs, understanding treatment options, and taking preventive measures, you can be a powerful advocate for your dog’s health and comfort.

References 

American Veterinary Medical Association. (2021). Cancer in pets. https://www.avma.org/resources/pet-owners/petcare/cancer-pets

National Canine Cancer Foundation. (n.d.). Types of cancer in dogs. https://wearethecure.org/learn-more-about-canince-cancer/common-types-of-canine-cancer/

Withrow, S. J., Vail, D. M., & Page, R. L. (2013). Withrow and MacEwen’s Small Animal Clinical Oncology (5th ed.). Elsevier Health Sciences.

American Kennel Club. (2020). Canine cancer: Types, symptoms, and treatment. https://www.akc.org/expert-advice/health/canine-cancer/