Cancer is a newly formed growth comprising incorrectly divided cells. Cancer differs from a tumor, but the two terms are used interchangeably. Dogs have two types of tumors, benign and malignant. 

Benign tumors are non-cancerous and do not spread. The word cancer describes malignant tumors that spread to other tissues and organs. 

Lymphoma, melanoma, mast cell tumors, osteosarcoma, hemangiosarcoma, breast cancer, fibrosarcoma, liver cancer, carcinoma, oral cancer, bladder cancer, transitional cell carcinoma, adenocarcinoma, brain tumors, oral melanoma, papilloma, stomach cancer, and testicular cancer are the most common types of cancer in dogs. 

Tumors on dogs are caused by genetic factors, DNA mutation, carcinogens, and viruses. Old age is a major risk factor. Early symptoms of cancer in dogs are skin lumps, non-healing sores, vomiting and diarrhea, appetite and weight loss, breathing or eating problems, and pain. 

Cancer growth in dogs is diagnosed with a microscopic examination of abnormal cell and tissue samples, combined with blood work and diagnostic imaging techniques. 

Different types of dog tumors require unique treatments, including options like surgery, radiation, chemotherapy, cryosurgery, and immunotherapy. Cancer is not always treatable, and it is the main cause of death in adult dogs. 

1. Lymphoma

Lymphoma is a group of malignant tumors that stem from white blood cells (lymphocytes). The effects of lymphoma depend on the type. 

Dogs have multicentric, mediastinal, gastrointestinal, cutaneous, and central nervous system lymphoma. 

The cause of canine lymphoma is unknown, but germs, chemicals, and strong magnetic fields are believed to play a role. 

Enlarged lymph nodes are a telltale sign. Other symptoms, depending on the lymphoma type, include coughing, shortness of breath, and stomach issues. 

Lymphoma is diagnosed with a fine needle aspiration (FNA) from a lymph node. Chemotherapy is the treatment of choice. 

Canine lymphoma is not preventable. Keeping the dog healthy helps reduce the risk of cancer. 

2. Melanoma

Melanoma is a benign or malignant tumor that stems from melanocytes or pigment cells. The tumor is locally aggressive and has a high spreading tendency. 

The benign form of melanoma occurs on the skin, while the malignant type usually affects the inside of the dog’s mouth. 

The cause of melanoma is uncertain. Sun exposure is a risk factor for melanoma in people, but it is unclear how it affects dogs. 

Signs of melanoma include bad breath, mouth bleeding, inability to eat, weight loss, enlarged lymph nodes, eye abnormalities, and pigmented skin lesions. 

Melanoma is diagnosed with a biopsy combined with imaging techniques. Standalone surgery or together with radiation therapy is used for treating melanoma. 

Minimizing exposure to the sun is recommended to reduce the risk of melanoma, although UV’s role in its development is unknown. 

3. Mastocytoma

Mastocytoma is a skin tumor arising from mast cells. Mast cell tumors are the most common cancer affecting the dog’s skin. 

The cause of mastocytoma is poorly understood. A mutated protein called KIT is known to contribute to its development. 

Signs of mastocytoma in dogs include a skin lump fluctuating in size, swollen local lymph nodes, local itchiness and inflammation, and an enlarged spleen and liver. 

Fine needle aspiration (FNA) and biopsy are the cornerstones of diagnosing mast cell tumors. The treatment is surgery to remove as much of the tumor as possible, followed by radiation or chemotherapy. 

A recent vaccine was developed for the treatment of mastocytoma, though mast cell tumors are currently not preventable. 

4. Osteosarcoma

Osteosarcoma is a highly aggressive bone cancer that develops in all dogs but is prevalent in large and giant breeds. 

The malignant bone cancer affects the long bones of the limbs and, in rare cases,  the spine, ribs, and skull bones. 

Osteosarcoma signs in dogs are limping, abnormal gait, swelling on the limbs, joint pain, loss of appetite, weight loss, and lethargy. 

Fine needle aspiration and biopsy diagnose osteosarcoma, while a chest X-ray checks for lung metastasis. 

Amputation of the affected limb is standard for managing osteosarcoma. Chemotherapy and radiation are considered if amputation is not an option. 

Osteosarcoma in dogs is not preventable, but frequent routine veterinary checkups help detect the condition early. 

5. Hemangiosarcoma

Hemangiosarcoma is an aggressive, fast-spreading cancer that rises from blood vessel cells. The tumor affects the spleen, heart, or skin. 

Spleen and heart hemangiosarcoma are prone to bursting and causing life-threatening bleeding. 

Skin hemangiosarcoma is associated with UV exposure, while the other types are with toxins, insecticides, and radiation, with the exact cause being undetermined. 

Signs of splenic hemangiosarcoma are distended abdomen, weakness, and pale gums. Heart hemangiosarcoma manifests with coughing, trouble breathing, exercise intolerance, weakness, and collapse. Skin hemangiosarcoma forms bleeding, red to purple skin lumps. 

A biopsy, fine needle aspiration, and X-ray imaging were used to diagnose hemangiosarcoma. Treatment includes surgery combined with chemo or radiation. 

Antiarrhythmic drugs, anti-bleeding medications, and blood transfusions are recommended in some cases. 

Hemangiosarcoma is not preventable. Routine veterinary exams every six weeks help catch the condition before it progresses.  

6. Breast Cancer

Breast cancer, or mammary cancer, is an umbrella term describing types of breast tissue tumors in dogs. Breast cancer is painful and affects the dog’s mobility when overgrown. 

The cause of breast cancer is not determined, but age and intact reproductive status are the two main risk factors. 

Signs of breast cancer are lumps around the nipples, discharge from the nipples, inflammation around the nipples, coughing, weight loss, and weakness. 

Diagnosing breast cancer requires fine needle aspiration or biopsy. The vet must determine the cancer type because dogs have different tumor types of different breast complexes. 

The treatment for dogs with breast cancer is surgery. Early spaying significantly reduces the risk of canine breast cancer. 

7. Fibrosarcoma

Fibrosarcoma is a connective soft tissue tumor. The most frequently seen fibrosarcoma location is beneath the dog’s skin. The mouth, nose, and bones are commonly affected, too. 

Large breeds like Irish Wolfhounds, Golden Retrievers, Gordon Setters, Doberman Pinschers, and Brittany Spaniels are predisposed to fibrosarcoma, which suggests the condition’s genetic etiology. 

Skin lumps, pain, lameness, trouble opening the mouth, bad breath, poor appetite, nasal discharge, and facial deformities are signs of fibrosarcoma in dogs. 

Fibrosarcoma is diagnosed with fine needle aspiration or biopsy. Surgery and radiation are the main treatment options. Anti-inflammatory medications and analgesics are prescribed to control the symptoms. 

Preventing fibrosarcoma is impossible, considering the poorly understood etiology and causes of the cancer. 

8. Liver Cancer

Liver cancer is a group of malignant tumors of the liver. The most common type is hepatocellular carcinoma (HCC). The tumor affects the liver’s function. 

The causes of liver cancer are not determined, but tumors are more frequent in dogs with previous liver damage or chronic inflammation. 

Signs of liver cancer include appetite loss, vomiting, diarrhea, lethargy, abdominal pain, ascites, enlarged liver, and jaundice. 

Liver cancer is diagnosed with blood work, diagnostic imaging, and biopsy. Surgery and chemo are used for managing liver cancer. 

Certain medications, such as S-adenosyl-methionine (SAMe) and silybin (milk thistle), help the liver regenerate. Preventing liver cancer is impossible. 

9. Carcinoma

Squamous cell carcinoma is a rare skin cancer that develops in multiple sites on light, hairless, or sparsely hairy body parts. 

Genetic and environmental factors lead to squamous cell carcinoma. The condition is frequent in Dalmatians, Beagles, and Bull Terriers that spend significant time outdoors. 

Firm and raised skin lesions, such as nodules and ulcerated plaques, are signs of squamous cell carcinoma. The tumors grow outward and resemble warts. 

Fine needle aspiration (FNA) and biopsy are the diagnostic procedures for carcinoma in dogs. Treatment is based on surgical excision. Radiation is considered if the surgical removal is incomplete. 

The risk of squamous cell carcinoma is reduced by keeping dogs inside and limiting extensive outdoor exposure. 

10. Oral Cancer

Oral cancer is a group of malignant tumors stemming from oral tissues. The top three oral cancers in dogs are melanoma, squamous cell carcinoma, and fibrosarcoma. 

The cause of oral cancer is unknown. German Shepherds, Weimaraners, Boxers, Chow Chows, and Miniature Poodles are at a higher risk,  confirming a genetic predisposition. 

Signs of oral cancer include drooling, bad breath, trouble chewing, bleeding, loose teeth, oral pain, visible mass in the mouth, deformed facial features, and weight loss. 

Oral cancer in dogs is diagnosed with fine needle aspiration. A biopsy is done if the FNA results are inconclusive. 

The treatment for oral cancer is surgery. Other options include radiation and immunotherapy. Oral cancer is not preventable based on current knowledge. 

11. Bladder Cancer

Bladder cancer is a group of cancers affecting the urinary bladder. The two most common types are transitional cell carcinoma and leiomyosarcoma. The cancers affect the dog’s ability to urinate and form metastases. 

The causes of bladder cancer in dogs are poorly understood, but they are believed to be the result of environmental and genetic factors. 

Signs of bladder cancer in dogs include dysuria (painful urination), stranguria (difficulty peeing), hematuria (blood in the urine), abdominal pain, anorexia, and lethargy. 

Abdominal ultrasound, aspiration, and biopsy are used to diagnose bladder cancer. Surgery is rarely applicable, and most dogs are managed with medications and chemotherapy. 

Bladder cancer is not preventable, but a healthy lifestyle reduces the risk of neoplastic conditions. 

12. Transitional Cell Carcinoma

Transitional cell carcinoma (TCC) is a cancerous tumor that rises from transitional epithelial cells. The cancer affects the dog’s bladder and urethra, causing difficulty urinating. 

TCC is considered genetic and is prevalent in Scottish Terriers, Shetland Sheepdogs, Fox Terriers, Beagles, West Highland White Terriers, Keeshonds, and Samoyeds. 

Signs of transitional cell carcinoma include stranguria (difficulty urinating), hematuria (blood in the urine), and unsuccessful urination attempts. 

Transitional cell carcinoma is diagnosed with urinalysis, abdominal ultrasound, and biopsy. A chest X-ray checks whether the cancer has affected the lungs. 

Surgery is not suitable for TCC because the cancer involves the part of the bladder responsible for control, and incontinence is a common side effect. 

Most TCCs in dogs are treated with medications, such as piroxicam and chemotherapeutics (mitoxantrone, carboplatin, and doxorubicin). 

Limit the dog’s exposure to carcinogens, provide a healthy diet, and maintain an optimal body weight to reduce the risk of transitional cell carcinoma. 

13. Adenocarcinoma

Adenocarcinoma is a tumor that stems from glandular tissue and occurs in many parts of the body. The anal glands, mammary tissue, and prostate are most commonly affected. 

Adenocarcinoma is assumed to develop due to genetic and environmental factors, but the exact cause is unclear.   

The signs of adenocarcinoma depend on the location of the tumor and include diarrhea, trouble breathing, straining to urinate, blood in urine, constipation, vomiting, weight loss, swelling of the abdomen, and enlarged lymph nodes. 

Adenocarcinoma is diagnosed with biopsy. Imaging techniques and bloodwork evaluate the tumor’s location and advancement. 

Surgery, chemotherapy, and radiation are possible treatment options. Pain management is vital for dogs with adenocarcinoma. 

Spaying eliminates the risk of mammary and ovarian adenocarcinoma, and neutering prevents testicular adenocarcinoma.  

14. Brain Tumors

Brain tumors are abnormal growths originating from brain tissues (primary) or metastatic spreads from distant cancers (secondary). Brain tumors  affect behavior, mentation, vision, and gait. 

Brain tumors have a complex etiology. Dolichocephalic breeds (Greyhounds, Dachshunds, and Collies) get meningiomas (tumors arising from the brain membranes), and brachycephalic dogs (Pugs, Bulldogs, Boston Terriers) get gliomas (tumors stemming from the brain or spinal cord).

Signs of brain tumors in dogs are head tilt, seizures, lack of coordination, increased reactivity, light sensitivity, vision problems, repetitive behaviors, and incontinence. 

Brain tumors are diagnosed based on clinical signs. Blood work helps rule out other conditions with similar signs, and imaging techniques evaluate whether the tumor has spread. 

The treatment includes a combination of surgery, radiation, and chemotherapy. Steroids slow down tumor growth, and antiepileptics manage seizures. Brain tumors are not preventable. 

15. Oral Melanoma

Oral melanoma is a malignant tumor that arises from pigment cells called melanocytes in the dog’s mouth. The tumor is aggressive and affects the dog’s ability to eat. 

The exact cause of melanoma in dogs is unknown. A combination of genetic and environmental factors is believed to be the culprit. 

Signs of oral melanoma are bad breath (halitosis), mouth bleeding, reluctance to eat, excessive drooling, weight loss, enlarged lymph nodes, and eye abnormalities. 

Oral melanoma is diagnosed with a biopsy, and imaging techniques are used to check if the tumor has spread. 

The treatment for oral melanoma includes surgery combined with radiation therapy. Canine oral melanoma is not preventable. 

16. Papilloma

Papilloma, or wart, is a benign tumor of the skin. Dogs develop papillomas in the mouth (oral papilloma), and the growths cause trouble eating once they are large enough. 

Papilloma is caused by the canine papillomavirus type 1 (CPV1), which dogs contract through direct contact with infected dogs. A weakened immune system is critical for infection. 

Signs of oral papilloma in dogs are cauliflower-like growths, mouth bleeding, halitosis or bad breath, drooling, reluctance to eat, anorexia, and weight loss. 

Veterinarians diagnose papilloma based on appearance, but a biopsy is necessary to be certain. 

Some papillomas resolve independently once the dog’s immunity recovers. Warts that fail to heal spontaneously are treated with interferon-alpha, antibiotics, topical creams, cryosurgery, and vaccines. 

Boosting the dog’s immune system is critical for preventing papilloma, especially in young puppies with underdeveloped immunities. 

17. Stomach Cancer

Stomach cancer is a tumor that forms in the dog’s stomach. The most common type is gastric adenocarcinoma. Stomach cancer affects the normal function of the stomach. 

The cause of stomach cancer is not understood. Chow Chows, Rough Collies, Staffordshire Bull Terriers, and Belgian Shepherds are predisposed, suggesting a genetic factor. 

Signs of stomach cancer include loss of appetite, chronic intermittent vomiting, and progressive weight loss. The signs are highly unspecified, resulting in delayed diagnosis. 

Stomach cancer is diagnosed with a biopsy. A tissue sample is collected via endoscopy, and the abdomen is examined on an X-ray or ultrasound. 

Treatment entails surgical removal of the affected part of the stomach. Chemotherapy and radiation are used when complete tumor incision is impossible. 

Feeding a high-quality and balanced diet paired with healthy body weight maintenance reduces the risks of cancer in dogs. 

18. Testicular Cancer

Testicular cancer is a group of malignant tumors of the testicles. The top three testicular tumors are seminomas, interstitial cell tumors, and Sertoli cell tumors, which affect the dog’s fertility. 

The causes of testicular cancer in dogs are unknown. Age and breed are risk factors since cancer occurs in German Shepherds, Weimaraners, Collies, Afghan Hounds, and Boxers over ten. 

Signs of testicular cancer are swollen and painful scrotum, asymmetrical testicles, and hind leg weakness or lameness. 

A scrotal ultrasound sets a diagnosis, which is confirmed with a biopsy. The recommended treatment is castration. Dogs with metastasized tumors are subdued to radiation or chemotherapy. 

Early neutering is the only method for preventing testicular cancer in dogs. The neutering time depends on the breed and is determined in consultation with the veterinarian. 

What is Cancer in Dogs?

Cancer in dogs is a newly formed and abnormal tissue. The new tissue grows uncontrollably and affects the function of the surrounding organs.

The word cancer is used interchangeably with tumor, although they are distinct. Tumors are benign (non-cancerous) or malignant (cancerous). The term cancer describes a cancerous tumor. 

Benign tumors are less invasive and do not spread to distant organs. Malignant tumors (cancer) are locally invasive and spread, causing metastases. 

Approximately one in four dogs develop cancer at some stage in their life, and almost half of the dogs over the age of ten have cancer, reports an article “Cancer in Pets” published by the American Veterinary Medical Association. 

Certain benign cancers are treatable and non-life-threatening. The majority of malignant tumors are fatal and warrant prompt and aggressive management. 

How Common Is Cancer in Dogs?

Cancer in dogs is very common. “Cancer is by far the leading cause of death in adult dogs,” according to a study, “An Investigation into Age, Size, and Breed-Related Causes of Death,” published in the Journal of Veterinary Internal Medicine in 2011. 

Scientists believe that cancer is increasingly common because modern veterinary medicine broke evolutionarily determined life expectancies. Dogs, simply put, live longer than expected. 

Commercial interbreeding for new breeds decreased the canine nucleotide diversity, increasing the risk of various cancer types. Obesity and modern carcinogens, such as second-hand smoke exposure and pollution, are other contributing factors. 

What Causes Cancer in Dogs?

The causes of cancer in dogs are listed below. 

• Genetics: Certain breeds, such as Bernese Mountain Dogs, Golden Retrievers, Boxers, and Rottweilers, are susceptible to cancer, indicating a genetic component. 
• DNA Mutation: Mutation of the cells is a determined cause of cancer in dogs. DNA mutations occur when cells divide incorrectly. 
• Age: Age is a significant risk factor for cancer. Old dogs with weak immune systems are unable to control mutated cells and have been exposed to carcinogens for longer. 
• Carcinogen Exposure: Established carcinogens are found in the food and environment and include certain preservatives, pesticides, second-hand cigarette smoke, smog, and air pollutants.  
• Viruses: Certain cancer types, such as papilloma, which is prevalent in young and immune-compromised dogs, are caused by a virus called the papillomavirus. 

What are the Early Signs of Cancer in Dogs?

The early signs of cancer in dogs are listed below. 

• Skin Lumps and Bumps: The emergence of lumps and bumps on the skin's surface is one of the earliest signs of cancer in dogs. 
• Non-Healing Wounds: Persistent skin sores or wounds that fail to heal are seen in dogs with cancer. 
• Appetite and Weight Loss: Dogs with cancer are reluctant to eat and start to lose weight. Some dogs retain normal appetites but become emaciated. 
• Vomiting and Diarrhea: Frequent or intermittent episodes of unexplained vomiting and diarrhea are common signs of canine cancer. 
• Trouble Eating or Breathing: Certain types or their metastases prevent normal eating or breathing, depending on the tumor location and size. 
• Bleeding from Body Openings: Bleeding from the mouth, nose, or genitals occurs in dogs with some cancer forms. 
• Unexplained Pain: Cancer is painful, which affects the dog’s behavior, causes anxiety or restlessness, and unprovoked vocalization, like crying or whining. 

How is Cancer Diagnosed in Dogs?

Cancer is diagnosed in dogs with physical exams and diagnostic procedures. The vet examines the dog and takes its detailed history. 

Initial diagnostic procedures include blood work, ultrasound, and X-rays. The cancer diagnosis is confirmed by microscopic examination of cell samples extracted via fine needle aspiration (FNI) or tissue samples (biopsy). Fine needle aspiration and biopsy give information about the tumor type and stage. 

Advanced imaging techniques, such as magnetic resonance imaging (MRI), positron emission tomography (PET), and computed tomography (CT), determine the tumor’s location and size. 

What Treatment Options Are Available for Cancer in Dogs?

Treatment options available for cancer in dogs are surgery, chemo, radiation, cryosurgery, and immunotherapy. 

Dietary changes support the dog’s general health, which improves its treatment response. Immune system support and pain management are vital aspects of cancer treatment. 

CBD (cannabidiol) is a novel supplement used in dogs with tumors. Cannabidiol has anti-cancer properties and boosts the effectiveness of chemo and radiation. 

The exact treatment option or combination is chosen based on the type and stage of the tumor. Certain tumors are not treatable, and the goal is to delay their spread while supporting the dog’s quality of life. 

What is the Prognosis for A Dog Diagnosed with Cancer?

The prognosis for a dog diagnosed with cancer depends on the cancer type and stage. Certain cancers cause early symptoms, which allows time for diagnosis and treatment. Others are insidious and remain asymptomatic until they advance. 

For example, dogs with lymphoma have a good prognosis and live for several years after diagnosis in many cases. 

Dogs with hemangiosarcoma have a poor prognosis. A dog dies from hemangiosarcoma every two minutes, according to the article “Hemangiosarcoma: A Deadly Canine Cancer That Strikes Without Warning,” published by the Morris Animal Foundation in 2024. 

Can Cancer in Dogs Be Prevented?

No, cancer in dogs cannot be prevented. Modern medicine does not offer a foolproof prevention method for canine cancer. 

The best strategy is to keep the dog generally healthy. Feed a high-quality diet, exercise regularly, maintain average body weight, and minimize exposure to known carcinogens. Early spaying and neutering reduce the risk of certain types of cancer in dogs.