Cancer is the uncontrolled growth of abnormal cells, and it is one of the most common serious illnesses in dogs, especially as they age. About 1 in 4 dogs will develop cancer during their lifetime, rising to about 1 in 2 dogs aged 10 or older.1 Some cancers are slow-growing and curable with surgery; others spread quickly. Many can be controlled for months or years, with a good quality of life.1,2 Early diagnosis makes a real difference, so knowing the warning signs and getting lumps checked matters.3 This guide covers the common types, risk factors, diagnosis, treatment options, quality of life and how to plan care with your vet.
See a vet promptly if your dog has:
- A lump that is pea-sized (1 cm) or larger and has been there for a month, or any lump that is growing or changing3,1
- A sore that won't heal, unexplained weight loss, or loss of appetite4,1
- Bleeding or discharge from the mouth, nose or other openings4,1
- Persistent lameness, or trouble breathing, urinating or passing stool4
Go to an emergency vet if your dog suddenly collapses, is very weak, or has pale gums or a swollen belly; these can be signs of internal bleeding from a tumor.5,6
What the Research Shows
- Common, especially with age. About 1 in 4 dogs will develop cancer in their lifetime, and about half of dogs aged 10 or older.1
- A leading cause of death. In UK primary-care records, cancer was the most common recorded cause of death, accounting for 16.4% of deaths.7
- Breed matters. In records of nearly 75,000 dogs seen at North American veterinary teaching hospitals, cancer caused 50% of deaths in Golden Retrievers, 47% in Bouviers des Flandres and 44% in Boxers.8,9
- Lymphoma is among the most common. It makes up to about a quarter of new canine cancers.10,11
- Chemotherapy is gentler in dogs than in people. At one teaching hospital, 20% to 30% of patients had mild side effects, about 5% to 8% needed hospital care, and about 1% died of complications.12
What Is Cancer in Dogs?
A tumor (neoplasm) is a growth of abnormal cells. Benign tumors grow slowly and don't spread, while malignant tumors (cancers) can invade nearby tissue and spread (metastasize) to other organs through the blood or lymphatic system.2,1 Not every lump is cancer. Many are harmless fatty lumps or cysts, but you can't tell by looking or feeling, so a sample is needed.3
Common Types of Cancer in Dogs
- Lymphoma: cancer of the lymphocytes, usually showing as swollen lymph nodes. See lymphoma in dogs.13
- Hemangiosarcoma: a cancer of blood vessel cells, often in the spleen or heart, that can cause sudden internal bleeding. See hemangiosarcoma in dogs.5,14
- Mast cell tumors: very common skin tumors, making up 11% to 20% of skin tumors. See mast cell tumors.15
- Osteosarcoma (bone cancer): 85% to 98% of primary bone tumors, mostly in large breeds. See bone cancer in dogs.15
- Oral tumors, including melanoma. See mouth cancer in dogs.15
- Mammary (breast) tumors, squamous cell carcinoma and others.1 See types of dog cancer.
Risk Factors
- Age: risk rises sharply in older dogs.1,9
- Size and breed: larger breeds are more likely to die of cancer, and Golden Retrievers, Bouviers des Flandres and Boxers have some of the highest rates of cancer deaths.9,8 Estimates for Golden Retrievers range from about 50% to 65% dying of cancer, depending on the study.8,16
- Neutering: in some breeds, especially Golden Retrievers, neutering has been linked with higher rates of certain cancers, but other research found no effect on cancer deaths. The effect varies by breed and sex, so talk to your vet.17,18,16
How Cancer Is Diagnosed
- Fine-needle aspirate: a quick, minimally invasive test that collects cells from a lump with a needle.3
- Biopsy: a tissue sample examined by a pathologist, recommended when a needle sample isn't conclusive.3,2
- Staging: blood tests, X-rays, ultrasound or CT to see whether the cancer has spread, which guides treatment and prognosis.2,13
Treatment Options
- Surgery to remove a tumor, which is often curative for small, localized tumors.3,1
- Chemotherapy, which in dogs aims to control cancer while keeping a good quality of life; side effects are usually mild.2,12
- Radiation therapy for tumors that can't be fully removed, or for pain relief.19
- Immunotherapy, such as the licensed canine melanoma vaccine for oral melanoma.20
- Palliative care: pain control, nutrition and comfort care when cure isn't possible.2
A board-certified veterinary oncologist can explain the options for your dog's specific cancer. Costs vary widely: at one university hospital, major surgery started at about $500, chemotherapy ranged from a few hundred to several thousand dollars over 3 to 6 months, and radiation cost about $2,500 to $7,000.2 See also diet for dogs with cancer.
Quality of Life and Saying Goodbye
The goal of most cancer care in dogs is to keep your dog comfortable and enjoying life for as long as possible. Quality-of-life scales can help. One widely used scale scores hurt, hunger, hydration, hygiene, happiness, mobility and "more good days than bad", and a total above 35 out of 70 is considered acceptable.21 Keep a simple diary of good and bad days, and talk openly with your vet. When pain or distress can no longer be controlled, choosing a peaceful euthanasia is a kind and loving decision.21
More reader questions about cancer are answered below.
Frequently Asked Questions
What are the first signs of cancer in dogs?
Lumps that grow, sores that won't heal, weight loss, loss of appetite, bleeding or discharge, lameness, and trouble breathing, eating or toileting. See signs of cancer in dogs.
At what age do most dogs get cancer?
Cancer is most common in older dogs; about half of dogs aged 10 or older develop it, though some cancers affect young dogs.
Which dog breeds get cancer most?
Golden Retrievers, Bouviers des Flandres and Boxers have some of the highest rates of cancer deaths, and larger breeds in general are at higher risk.
How long can a dog live with cancer?
It depends entirely on the type and stage. Some cancers are cured with surgery, while others progress in weeks or months. Your vet can give a prognosis for your dog's cancer.
Are dogs with cancer in pain?
Some cancers are painful, especially bone and mouth tumors, but pain can usually be managed with vet-prescribed medicine.
Is it worth treating a dog with cancer?
Often, yes. Treatment in dogs focuses on quality of life, and side effects are usually mild. Your vet can help you weigh the options.
When should I put my dog down with cancer?
When pain or distress can't be controlled and bad days outnumber good ones. A quality-of-life scale and your vet can help you decide.
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Sources and further reading
This article was rewritten and fact-checked on October 16, 2026 against current veterinary references and specialist guidelines:
- American Veterinary Medical Association. Cancer in pets. AVMA pet owner resource (n.d.).
- Cornell University Hospital for Animals. Cancer management: frequently asked questions (n.d.).
- Ettinger SN. Tumor Detection in Dogs and Cats: See Something, Do Something. Today's Veterinary Practice, Jul/Aug 2017.
- Tufts University / Your Dog newsletter. 10 Warning Signs of Cancer (lists the Veterinary Cancer Society's 10 signs; n.d.).
- Cornell Richard P. Riney Canine Health Center. Hemangiosarcoma in dogs (n.d.).
- American College of Veterinary Surgeons. Splenic Masses (n.d.).
- O'Neill DG, Church DB, McGreevy PD, Thomson PC, Brodbelt DC. Longevity of UK Dog Breeds. SVEPM proceedings (VetCompass data 2007–2011).
- University of Georgia News. Landmark UGA study reveals breed-specific causes of death in dogs (2011). (press coverage)
- Fleming JM, Creevy KE, Promislow DEL. Mortality in North American dogs from 1984 to 2004: an investigation into age-, size-, and breed-related causes of death. J Vet Intern Med 2011;25(2):187–198. doi:10.1111/j.1939-1676.2011.0695.x
- Veterinary Cancer Society. Pet Owners (n.d.).
- Hyland K, Weir M, Barnette C. Lymphoma in Dogs. VCA Animal Hospitals (n.d.).
- Iowa State University Lloyd Veterinary Medical Center, Oncology. Oncology FAQ (client flyer, n.d.).
- Fan TM. Overview of Canine Lymphoma. Merck Veterinary Manual, Professional Version. Reviewed Sep 2023, modified Apr 2025.
- University of Minnesota, Modiano Lab. Hemangiosarcoma detailed article (n.d.).
- National Cancer Institute, Center for Cancer Research, Comparative Oncology Program. Disease info (n.d.).
- Kent MS, Burton JH, Dank G, Bannasch DL, Rebhun RB. Association of cancer-related mortality, age and gonadectomy in golden retriever dogs at a veterinary academic center (1989–2016). PLoS ONE 2018;13(2):e0192578. doi:10.1371/journal.pone.0192578
- Torres de la Riva G, Hart BL, Farver TB, Oberbauer AM, Messam LLMcV, Willits NH, Hart LA. Neutering dogs: effects on joint disorders and cancers in Golden Retrievers. PLoS ONE 2013;8(2):e55937. doi:10.1371/journal.pone.0055937
- Hart BL, Hart LA, Thigpen AP, Willits NH. Assisting decision-making on age of neutering for 35 breeds of dogs: associated joint disorders, cancers, and urinary incontinence. Front Vet Sci 2020;7:388. doi:10.3389/fvets.2020.00388
- University of Tennessee College of Veterinary Medicine. Veterinary radiation oncology for pets. UTCVM.
- JAVMA News. USDA licenses DNA vaccine for treatment of melanoma in dogs (1 Mar 2010).
- Villalobos A. Quality of Life Scale (HHHHHMM). Veterinary Practice News (n.d.).
About this article
Last updated : fully rewritten using AVMA, Veterinary Cancer Society, Cornell, Merck Veterinary Manual and peer-reviewed research on cancer rates, breed risk and treatment; added a research summary, quality-of-life guidance and FAQ.
This page is for general information and is not a substitute for an exam by your veterinarian.
