Causes

When it comes to cancer—whether in humans or dogs—there is rarely a single cause. Many factors can contribute, and in most cases, it’s a combination of several. It’s natural to feel overwhelmed or even blame yourself after a diagnosis, but it's important to understand: some causes are entirely out of your control.

That being said, learning about the possible causes and taking preventative steps can make a difference in your dog’s long-term health.

Genetics and Heredity

Genetic Causes of Canine Cancer

One of the most overlooked causes of cancer in dogs is heredity. Your dog may inherit certain gene mutations from their parents that increase their cancer risk. These include:

• Tumor Suppressor Genes

  • Normally prevent uncontrolled cell growth

  • When mutated, they lose this ability, leading to cancer development

  • Involved in cancers like osteosarcoma, melanoma, breast cancer, and hemangiosarcoma

• Proto-Oncogenes

  • These genes help regulate normal cell growth and division

  • When mutated or overexpressed, they become oncogenes, which promote uncontrollable cell replication

• DNA Repair Genes

  • Their job is to fix mistakes during DNA replication

  • When faulty, they fail to repair mutations—allowing abnormal, cancerous cells to multiply

In general, larger dog breeds are more likely to develop cancer than smaller breeds. Knowing your dog’s breed-related risks can help with early detection and proactive care.

*Tip: If you're concerned about your dog’s genetic risk for cancer, speak to your veterinarian, and they can recommend screenings or early lifestyle adjustments.

Environment

Exposure to Chemicals

• Cleaning products: chlorine, bleach, formaldehyde, etc.

  • Contain endocrine disrupters that disrupt hormone production and affect cellular functions

• Household items: batteries, mattresses, etc.

  • Can often contain toxins like lead and lithium in batteries and flame-retardant products in mattresses

• Certain foods

  • Some are infected by aflatoxins - toxins produced by fungi in many agricultural products

  • Could have been treated with pesticides

  • Processed with high heat - could release carcinogens

*Extreme/prolonged exposure to & accumulation of chemicals in the body can increase risk of cancer 

Pollution

• Tobacco & Smoke Exposure

  • Dogs exposed to tobacco smoke are at increased risk of nasal cancers

  • Secondhand marijuana smoke contains many of the same toxins as cigarettes—some in higher amounts

  • Vape mist pose similar risks by containing carcinogens (e.g., benzene) and ultrafine particles

  • Recommendation: Avoid smoking cigarettes, marijuana, or vaping around dogs

• Indoor Heating & Fuels

  • Coal-burning appliances and kerosene heaters can increase risk of nasal and lung cancers

  • Dogs can serve as early indicators (or "sentinels") of environmental cancer risks for humans

• Contaminated Drinking Water

  • Tap water contaminants may increase risk of bladder cancer in dogs

  • Trihalomethanes (water disinfectant byproducts) can increase cancer risk

  • Tip: Use filtered water, especially in industrial areas

• Air Pollution

  • Dogs in areas with heavy air pollution (especially Boxers) show higher rates of lymphoma

  • Pollutants like lead, benzene, and asbestos are known carcinogens

• Synthetic Chemicals

  • PFCs (Perfluorochemicals): Found in water/stain repellents on furniture, fabrics, and cookware

  • PBDEs (Polybrominated Diphenyl Ethers): Flame retardants in cushions, fabrics, and household plastics

  • Studies have linked both to tumors in some animals; ongoing research is evaluating risk in dogs

• Industrial Pollutants

  • Vinyl Chloride: A carcinogenic gas used in PVC/vinyl production; dogs can be exposed through air or groundwater near manufacturing plants

  • Asbestos: Long-term exposure can cause lung cancer or mesothelioma in dogs

Risk Factors

• • Living near or in:

    • Industrial zones

    • Agricultural areas

    • Polluted cities or smog-heavy environments

  • Prolonged exposure to environmental toxins

  • Chewing on contaminated or synthetic items

  • Living with smokers

• Cancer development depends on:

  • Type & concentration of the pollutant

  • Duration of exposure

  • Your dog’s ability to detoxify or neutralize chemicals

Prevention Tips

• • Don’t smoke or vape around pets

  • Filter your dog’s drinking water

  • Replace furniture/products with synthetic flame retardants

  • Choose items not treated with water/stain repellents

  • Use stainless steel or ceramic dog bowls rather than plastic

  • Avoid coal and kerosene heaters

  • Consider relocating from heavily polluted areas

Agricultural Products

Pesticides

• Common Uses

  • Applied to eliminate pests like flies, mites, spiders, and rodents

  • Found in flea shampoos, dips, sprays, and tick collars

  • Some harmful ingredients:

    • Organophosphates: toxic to mammals, disrupt neurotransmitters → tremors and convulsions

    • Pyrethrins: target the central nervous system → hyperactivity and paralysis

    • Carbamates: deregulate nervous system → rapid spasms and seizures

• Health Risks

  • Prolonged exposure linked to various dog cancers

  • Especially risky when used frequently or combined with other chemicals

Herbicides

• Common Uses

  • • Used to kill unwanted plants/weeds in lawns, golf courses, athletic fields, etc.

  • Possible chemicals included: Glyphosate, 2,4-D (component used in Agent Orange)

  • Environmental Spread: 

  • Chemicals can:

    • Run off into waterways

    • End up on the ground your dog walks or rolls on

    • Be present in contaminated ingredients used in some pet foods

Cancer Risks in Dogs

• Transitional Cell Carcinoma (Bladder Cancer)

  • Develops in the lining of the bladder and urinary tract

  • Strongly linked to herbicide exposure (especially lawn care chemicals)

  • Less strongly linked to insecticides

• Malignant Lymphoma

  • Associated with exposure to 2,4-D in herbicide-treated lawns

  • Risk increases with frequency of chemical application

• Risk Factors

  • Exposure frequency: Dogs who spend more time on treated lawns have higher risk

  • Breed sensitivity: Scottish Terriers have a higher genetic risk for bladder cancer

  • Weight: Overweight/obese dogs are more likely to develop transitional cell carcinoma

Risk Reduction

• Stop or limit lawn chemical use in your yard

• Use natural, herbicide-free alternatives: 

  • Control weeds organically with compost or manual weeding

• Limit outdoor time in public parks or spaces that may use chemicals

  • Ask park managers for a list of lawn care chemicals used

• Wipe down your dog with pet-safe wipes after walks

• Bathe your dog regularly to remove lingering chemical residues

Radiation

UV Radiation

• Types of UV Rays

  • UVA:

    • Makes up 95% of UV rays

    • Longer wavelengths → penetrates deep into skin → damages skin cells

  • UVB:

    • Shorter wavelengths

    • Causes sunburn and DNA damage in skin cells → increases skin cancer risk

• Skin Cancer in Dogs

  • Caused by overexposure to UV rays

  • DNA damage from sunburn may lead to uncontrolled cell growth → cancer

• Protection

  • Limit sun exposure to 15–20 minutes during low UV times (early morning or late evening)

  • Extra caution for dogs with light or thin coats, shaved fur, exposed or pink skin

  • Provide shade for outdoor pets

  • Be cautious at higher elevations (UV exposure increases)

  • Apply pet-safe sunscreen to sensitive areas (nose, ears, abdomen)

Ionizing Radiation

• High-energy radiation like X-rays and gamma rays can damage DNA

• Sources include:

  • Natural: radon gas in soil, rocks, and buildings (especially in basements)

  • Medical: diagnostic imaging (X-rays, CT scans)

  • Environmental: nuclear accidents, irradiated foods, airport scanners

• Radiation Therapy

  • Used to treat cancer, but high doses may mutate nearby cells

  • Rare risk: secondary tumors forming from surviving cells

• Acute Radiation Syndrome (ARS)

  • Caused by sudden, large exposure to radiation

  • Symptoms:

    • Vomiting

    • Diarrhea

    • Fever

    • Seizures

    • Loss of appetite

Cancers Linked to Radiation

• Most common: bone cancer (due to high density of bone absorbing radiation)

• Other risks:

  • Liver tumors

  • Lung cancer

  • Heart tumors

Radiation Protection

• Risk is generally low, but still important to:

  • Limit medical radiation and only use imaging tests when necessary

  • Use protective shielding on non-target areas during X-rays or scans

Diet

Foods to Avoid

• Grains and starches cooked at high temperatures (especially dry heat):

  • Common in commercial dog foods

  • High-heat processing can produce cancer-promoting compounds like Acrylamide

• Aflatoxins:

  • Carcinogenic compounds from moldy crops (corn, wheat, dairy)

  • Risk from contaminated ingredients in poorly preserved food

Prevention Tips

• Choose dog foods with:

  • Fresh, preservative-free ingredients

  • Omega-3 fatty acids (anti-inflammatory)

  • Human-grade quality (more regulated)

• Discard any moldy food immediately

• Opt for brands that disclose their cooking processes: some high-end brands cook at lower temperatures

• Organic foods = lower pesticide exposure

Nutritional Defense

• Feed a balanced diet rich in natural antioxidants like broccoli, squash, spinach, and sweet potatoes

  • These can help dogs fight carcinogens

Acrylamide

What is it?

• A cancer-causing compound formed during high-temperature cooking

• Created by the Maillard reaction: sugars + amino acids react under heat

• Found in many dry commercial dog foods

Risk in Dog Foods

• Dogs often eat dry food as their sole diet, increasing risk of chronic exposure

• Ingested acrylamide turns into glycidamide, a toxic byproduct linked to cancers of:

  • Mammary glands

  • Lungs

  • Thyroid

  • Testicles

  • Skin

  • Other organs

• Acrylamide exposure in dogs is estimated to be 4× higher than in humans

• Some dog foods contain levels of acrylamides 122× higher than human food

Reduce Risks

• Safer Food Choices

  • Raw diets (lower acrylamide levels), but be aware of risks of bacterial contamination

  • Home-cooked meals:

    • Control temperature and cooking time

    • Avoid browning food excessively

    • Use boiling or steaming methods (these don’t produce high levels of acrylamide)

    • Cook to doneness, not crispness: browning = higher acrylamide levels

  • Focus on:

    • Minimally processed foods

    • Ingredients like meat, fish, and dairy (produce less acrylamide when cooked)

Other Factors

Age

• With age, the immune system may weaken → harder to detect and destroy cells with mutations.

• Cell division becomes less accurate with age:

  • Errors in DNA replication may go unrepaired

  • These mutations can eventually become cancerous

• Longer lifespans = longer exposure to carcinogens like radiation, chemicals, and processed foods that can alter DNA over time

Virus and Infection

• Oral papillomas:

  • Benign warts in a dog’s mouth caused by a virus

• Canine Transmissible Venereal Tumor (CTVT):

  • A sexually transmitted cancer

  • Spread via direct contact (usually during mating)

  • Rare but contagious: involving transfer of cancerous cells from one dog to another

Injury

• Serious trauma (bone fractures, surgical implants):

  • Can create sites more prone to cancer development

  • Sarcomas are more likely to form at locations with:

    • Fractures

    • Pins

    • Plates or other metal implants

Spaying/Neutering

Benefits

• Spaying/neutering reduces behavioral risks:

  • Decreases aggression and territorial marking

  • Lowers the urge to roam → reduces risk of accidents (e.g., being hit by a car)

• Reduces risk of hormone-related cancers:

  • Spaying helps prevent mammary, ovarian, and testicular cancers

Risks

• Some studies suggest it may increase risk of other cancers:

  • Osteosarcoma (bone cancer)

  • Hemangiosarcoma (blood vessel cancer)

  • Prostatic adenocarcinoma (prostate cancer)

  • Transitional cell carcinoma (bladder cancer)