How To Recognize A Cancerous Tumor On Dog

Recognizing a cancerous tumor on your dog can involve several steps. The first sign may be an abnormal lump or bump on your dog’s body. Not all tumors are cancerous, but it’s important to get any new lumps checked out by a vet.

Other signs could include dramatic weight loss, loss of appetite or difficulty eating, lethargy, or a change in behavior such as increased aggression or depression. These signs could also indicate other medical conditions, some of which could be life-threatening.

Please remember this information can help you identify possible signs but it’s not definitive. Always consult with a veterinary professional if you suspect your dog may have a tumor. Early detection can greatly improve your dog’s prognosis.

Last Updated on September 20, 2023

Have you by any chance noticed a suspicious lump on your dog? If you have, then your mind must be racing with lots of negative thoughts and questions by now. But keep your shirt on because not all lumps you find are cancerous. And definitely doesn’t mean they are going to die. If you’re looking to find a guide on cancerous tumors in dogs, then this is for you. Keep reading to find out the common types of cancer in dogs, how to recognize suspicious masses, and if they can be prevented.

Let’s get right to it, shall we?

Great Dane

Common types of cancerous tumors

Mast cell tumors

Mast cell tumors are the most common malignant tumor in dogs. Mast cell tumors develop from, as you guessed it, mast cells. Mast cells are responsible for allergic reactions and are located throughout your dog’s body. With that in mind, mast cell tumors can develop anywhere on the body. However, they are most commonly found in the lower abdomen, chest, and back of the upper thighs. This type of tumor grows quickly, are usually red, and very itchy.

Additionally, any breed and age can get mast cell tumors. But you’ll find that Boxers, Pugs, and Bulldogs are more susceptible to the disease. Dogs aged 8-10 years old are also prone to developing this illness. What do they look like? Mast cell tumors typically appear like a lump that may be soft or solid to touch. To the untrained eye, it may resemble a lipoma – a benign tumor. And this is where most people run into trouble.

Tumor size at the time of surgery depicts your pet’s survival rate. Actual mast cell tumors may be downplayed as benign and can become worse when not treated. This is why any suspicious mass must be checked by your veterinarian.


Lymphoma is also one of the most common cancers found in dogs. It’s a disease caused by the growth of lymphocytes in the body. They usually grow in the lymphoid tissues found in the bone marrow, thymus, lymph nodes, or spleen. Other sites are the eyes, skin, central nervous system, and bone. This type of cancer can affect dogs of any breed and age. But they are most common in Golden retrievers and Standard poodles aged 6-9.

On the brighter side, dogs diagnosed with lymphoma – especially when caught at an early stage – are considered treatable. Some of the symptoms of lymphoma are lethargy, coughing, and a swollen lymph node. 

Labrador Retriever


Melanoma is a skin cancer often found in dogs with dark pigment skin. This type of cancer arises from pigment-producing cells called melanocytes. They can be categorized as malignant or benign. Luckily, benign tumors are more common than malignant ones. Most melanomas found in dogs are considered to be harmless. Thus, surgical removal is only needed to cure the condition. How does it appear?

Like other cancerous tumors, melanomas appear as a lump or mass but with a darker surface color. Some may also look like a large, wrinkled mass that may or may not be dark in color. Any dog of breed and age can have melanomas. But malignant melanomas are more common in older dogs. Also, males are usually the one who gets affected than females. The common sites of development are in the lips, mouth, and nail beds. 

Furthermore, this disease has a high tendency of spreading. This is why after surgery, chemotherapy or immunotherapy is recommended as an additional treatment.


Osteosarcoma is a common type of bone cancer in canines. It’s responsible for up to 85% of tumors found in the skeletal system. Although it mostly affects large breeds like Great Danes and Greyhounds, again, it can happen to dogs of any age and breed. A dog usually gets diagnosed with this cancer because of a limping leg. Bones in the shoulder, wrist, and knees are also most affected. 


Hemangiosarcoma is a cancer that develops in the blood vessel. Typically, it affects the spleen, liver, skin, or heart. This type of cancer mostly develops in middle-aged and elderly dogs. Certain breeds like Golden Retrievers and German Shepherds are found to be more at risk of acquiring this. For that reason, veterinary hospitals like the Prestige Animal Hospital recommends dog owners with these breeds take their pups for screening after age 5. This condition develops slowly and isn’t noticeable until their advanced stage. Detecting this type of cancer earlier is the key. 


Histiocytomas are benign tumors found in younger dogs. This type of tumor develops from their immune system and are common in English Bulldogs, Scottish Terriers, Greyhounds, Boxers, Boston Terriers, and Chinese Shar-Peis. This type of tumor will appear as a small, red, hairless, raised, and sometimes ulcerated lump. Surgical removal is not required to remove the tumor as they disappear within 2-3 months. But you may choose to remove it, especially if it becomes bothersome to the dog. 



It may come as a surprise, but some lumps you find may be caused by a virus. A great example of this would be papilloma. Papilloma or also known as warts are caused by a virus called papillomavirus. Dogs who catch this virus develop cauliflower-like warts typically on their lips, inside the mouth, and around the eyes. But where do they get this virus? A dog can get infected when he comes into direct contact with an infected dog or a contaminated object. Should they be removed? It depends.

Warts can regress on their own after a few weeks or months. However, severe infections can be painful and can make chewing and swallowing difficult for your pup. If this is the case, then surgically removing them is the best option. Your veterinarian may also provide supplements that can help boost your dog’s immune system to naturally remove warts.

Skin Tags

Another non-cancerous lump you may feel on your dog is skin tags. Skin tags also have an unusual form and can easily be mistaken as a cancerous lump. To know the difference, you can read Can Dogs Get Skin Tags?

Recognizing cancerous tumors

With several types of cancer written in books, how can we be sure that one lump we find is not cancerous? The answer: We can’t. We simply aren’t trained to diagnose unusual growths in our dog’s body. This is why we need the expert opinion of our veterinarian. Cancer is a disease that’s best treated early on. For this reason, pet owners need to observant of any warning signs of cancer. Here are some of them:

  • Lethargy or weakness
  • Difficulty swallowing or eating
  • Persistent lameness
  • Sores that don’t heal
  • Reluctance to exercise
  • Poor appetite
  • Weight loss
  • Abnormal swelling
  • Change in bathroom habits
  • Bleeding

For suspicious lumps, here are some of the things you should also look out for:

  • If it’s changing or growing quickly
  • It looks discolored.
  • Cancerous lumps often have a fleshy but solid feel

Yorkshire Terrier

Can it be prevented?

Sadly, most dogs develop cancer because of genetic predisposition. This means that owners can’t do much to avoid their dogs from getting ill. But owners can make conscious choices to reduce the risk of their dogs developing cancer. The first one would be whether to spay-neuter their dog. Some breeds benefit from being spayed while some may actually increase their risk for cancer when spayed or neutered before sexual maturity. Discussing with your veterinarian about the pros and cons of spaying can aid you in this decision.

Another thing you can do is managing your dog’s weight and supplement it with antioxidants. Obesity is often linked to joint pains and developing more tumors. Choose a dog food that is rich in nutrients. In this way, he is still getting the essential vitamins he needs without eating a lot. Additionally, you can also add more antioxidants like EPA and DHA to your pup’s diet. These antioxidants are known to prevent damage in the cells – an important factor if you want to avoid cancer. Fish oil is rich in these antioxidants.


Lumps found in dogs can mean a lot of things. This doesn’t mean, however, that we shouldn’t take them seriously. Cancerous lumps do not go away on their own but on the contrary, become worse if left untreated. If you find an unusual mass on your dog, don’t hesitate to tell your veterinarian. It might just be a benign tumor that would go away on its own.





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