Signs of Cancer in Dogs: What to Check and When to Act

Cancer kills more dogs over the age of 10 than any other cause. Some of it is untreatable when found. A lot of it is treatable when found small, and the difference is usually whether someone put their hands on the dog and acted on what they felt.

Ten warning signs

1. A new lump, or an existing one that grows, changes or bleeds
2. A sore that does not heal
3. Weight loss without a change in food
4. Loss of appetite, or difficulty eating or swallowing
5. Bleeding or discharge from the mouth, nose, or under the tail
6. A bad smell from the mouth or elsewhere
7. Lameness or stiffness that does not resolve, especially in a large breed (bone cancer)
8. A swollen belly, or sudden weakness and pale gums (internal bleeding from a splenic tumor)
9. Difficulty breathing, urinating or defecating
10. Persistent lethargy or a change in behavior

Every lump gets a needle

The single most useful rule for a senior dog owner. A fine-needle aspirate is quick, cheap, usually needs no sedation, and separates a harmless lipoma from a mast cell tumor or soft tissue sarcoma. Measure and photograph lumps with a ruler; any lump larger than a pea that has been there a month, or any lump that grows, goes to the vet.

Cancers by breed

Breed risk is real and worth knowing. Golden Retrievers: hemangiosarcoma and lymphoma. Boxers: mast cell tumors, lymphoma and brain tumors. Bernese Mountain Dogs and Flat-Coated Retrievers: histiocytic sarcoma. Rottweilers, Great Danes, Greyhounds and Irish Wolfhounds: osteosarcoma. Scottish Terriers and Shetland Sheepdogs: bladder cancer. The breed pages list what to watch for.

Treatable when caught early

• Skin and subcutaneous tumors (mast cell tumors, soft tissue sarcomas): surgery with clean margins is often curative.
• Lymphoma: chemotherapy puts most dogs into remission with good quality of life; median survival around a year, some much longer.
• Splenic masses: emergency surgery when they bleed; some are benign.
• Mammary tumors: half are benign; early spaying reduces risk sharply.
• Bladder cancer: a urine test can screen high-risk breeds; drugs slow it.

Harder: osteosarcoma (amputation plus chemotherapy extends life but rarely cures), hemangiosarcoma (often found when it bleeds), brain tumors.

What you can do

Monthly hands-on lump checks. A same-day appointment for sudden weakness or a swollen belly in a large older dog. Bloodwork twice a year. Keep the dog lean: obesity is linked with several cancers. And if there is a diagnosis, ask about a referral to a veterinary oncologist before deciding; options are often better than expected.