Signs of Cancer in Dogs: What to Watch For and When to Act

Hearing that a dog may have cancer is scary for any pet owner. While cancer is more commonly diagnosed in senior dogs, it can occur at any age. Early recognition and routine veterinary exams play an important role in identifying problems sooner, when more treatment options may be available, and quality of life can often be better supported.

Cancer develops when abnormal cells grow in an uncontrolled way and can invade nearby tissues or spread to other parts of the body. Because many early changes are subtle, knowing what to watch for at home and partnering closely with your veterinarian will make sure that any concerns are evaluated as soon as possible.

What Causes Cancer in Dogs?

There is rarely a single cause. Cancer develops due to genetic mutations within cells, and several factors may contribute. Age is one of the most significant risk factors. As dogs live longer thanks to advances in nutrition and veterinary care, they have more time to develop age-related diseases, including cancer.

In addition to age, several factors may influence a dog’s risk for developing cancer. Genetics, environmental exposures, and chronic inflammation are all believed to play a role. Some breeds have a higher incidence of certain cancers. For example, Boxers, Golden Retrievers, Labrador Retrievers, Rottweilers, and Bernese Mountain Dogs are more commonly diagnosed with cancers such as lymphoma, mast cell tumors, osteosarcoma, and hemangiosarcoma.

Breed history is one reason your veterinarian asks detailed questions during wellness visits, as it helps guide screening recommendations and what changes to monitor more closely over time. While cancer cannot always be prevented, regular physical exams and evaluation of new lumps, swelling, or changes in behavior can help with earlier detection and more timely treatment.

Common Signs of Cancer in Dogs

The signs of cancer in dogs can vary widely depending on the type and location of the disease. Some dogs show obvious symptoms, while others experience subtle changes that are easy to overlook. Paying attention to new or persistent abnormalities is essential.

• New lumps or bumps, or growths that change in size or appearance
• Swollen lymph nodes
• Wounds that do not heal
• Unexplained weight loss
• Loss of appetite
• Lethargy or decreased activity
• Limping or persistent pain
• Difficulty eating, swallowing, or breathing
• Abnormal bleeding or discharge

Not every lump is cancerous. Many skin masses in dogs are benign. However, any new mass should be evaluated by a veterinarian. A simple diagnostic test, such as a fine needle aspirate, can often help determine the nature of a lump.

Common Types of Dog Cancer

There are many different types of cancer in dogs, and each behaves differently. Some remain localized and grow slowly, while others are more aggressive and can spread to other parts of the body. Knowing the typical signs and which dogs may be at higher risk can help support earlier evaluation.

Lymphoma

Lymphoma is one of the most frequently diagnosed cancers in dogs and affects lymphocytes, a type of white blood cell. It commonly presents as enlarged, firm lymph nodes under the jaw, in front of the shoulders, or behind the knees. Breeds such as Boxers, Golden Retrievers, Labrador Retrievers, and German Shepherds are diagnosed more often than others. Many dogs otherwise feel well at the time of diagnosis, which is why routine exams and checking for new swellings at home are important.

Mast Cell Tumors

Mast cell tumors are among the most common skin cancers in dogs. They can vary widely in appearance, ranging from small, hairless bumps to larger, reddened or ulcerated masses, and they may change in size from day to day. Boxers, Boston Terriers, Labrador Retrievers, and Pugs have a higher incidence. Any new skin mass should be evaluated by your veterinarian, as early sampling helps guide treatment decisions.

Osteosarcoma

Osteosarcoma is an aggressive bone cancer most often seen in large and giant breed dogs, including Rottweilers, Great Danes, Irish Wolfhounds, and Greyhounds. It typically affects the long bones of the limbs. Persistent lameness, swelling near a joint, or signs of bone pain warrant prompt veterinary attention, as these symptoms are often initially mistaken for arthritis or injury.

Oral and Nasal Tumors

Tumors of the mouth and nasal passages can occur in any breed but are seen more frequently in older dogs and certain large breeds. Oral tumors may be malignant, such as melanoma or squamous cell carcinoma. Signs can include bad breath, drooling, bleeding from the mouth, difficulty chewing, facial swelling, nasal discharge, or nosebleeds. Because many of these changes develop gradually, regular oral exams during wellness visits are essential for early detection.

Dog Cancer Treatment Options

Dog cancer treatment depends on the type of cancer, its stage, and your dog’s overall health. Treatment plans are individualized and may include one or more approaches.

• Surgery: Often used to remove localized tumors.
• Chemotherapy: May be recommended for cancers like lymphoma or when there is risk of spread.
• Radiation therapy: Used for certain tumors that cannot be completely removed surgically.
• Palliative care: Focuses on comfort and quality of life when curative treatment is not possible.

Advances in veterinary oncology have expanded available therapies, and many dogs tolerate treatment better than owners expect. Your veterinarian may refer you to a board-certified veterinary oncologist for specialized care.

Why Early Detection Matters

When cancer is detected before it spreads, treatment options may be broader and more effective. Early-stage tumors may be surgically removed with cleaner margins, potentially reducing the risk of recurrence. In other cases, early diagnosis allows for more timely use of chemotherapy, radiation therapy, or other supportive treatments.

The American Veterinary Medical Association notes that regular veterinary checkups are critical for early disease detection, including cancer. Routine wellness exams give your veterinarian the opportunity to palpate lymph nodes, examine the skin, evaluate the oral cavity, and identify subtle changes you may not notice at home.

When to Schedule a Veterinary Appointment

Any new lump, persistent lameness, unexplained weight loss, or behavioral change warrants a veterinary visit. Trust your instincts. If something feels different about your dog’s health or demeanor, it is worth having it evaluated.

Annual or semiannual wellness exams are especially important for senior dogs, as cancer in dogs becomes more common with age. Early recognition of warning signs allows for timely diagnostics and informed decisions about care.

If you have questions, we would love to answer them for you. Please give us a call at the office at (254) 935-3693, or you can email us at info@beltonvetclinic.com. Our staff would love to talk with you!

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