Most Common Cancers in Dogs

Cancer in dogs is something we never want to see happen, especially since dogs are our best friends. We must be aware of the signs of cancer in dogs to watch for.

· 7 min read

Cancer in dogs is something we never want to see happen, especially since dogs are our best friends. However, we haven’t yet found a way to prevent genetic health issues such as cancer and disease from affecting our dogs. Therefore, we must be aware of the signs of cancer in dogs to watch for.

It’d also be wise to educate ourselves on the most prevalent forms of cancer in dogs. After all, the sooner we catch the signs and symptoms, the more likely we are able to get treatment for our beloved pets before it’s too late.

Many of the cancers that affect dogs are similar to the cancers found in humans, which can make the treatment and diagnosis process a little easier for us to understand. Even the symptoms are very similar, which can make it easy to spot when your dog doesn’t quite seem like themselves. In this guide, we’ll take you through some of the most common canine cancers and what you need to know.


What are the Signs of Cancer in Dogs?

There are signs and symptoms of cancer in dogs that vary depending on the type of cancer, but there are core symptoms that remain the same. Understanding this can help give you a clearer idea of what you need to be looking out for if you’re worried that your dog might be sick.

Some possible symptoms of cancer in dogs include:

  • Lumps beneath the skin. Usually, these are hard, unlike soft fatty deposits
  • Trouble with swallowing food or water
  • Difficulty going to the bathroom (often straining with nothing coming out)
  • Sores on the body that won’t heal
  • Swelling and inflammation in the body
  • General pain, lameness, or difficulty getting up
  • Weight loss and a loss of appetite
  • Coughing, wheezing, or general trouble with breathing
  • Lethargy and a general disinterest in playing and exercise (depression)
  • Unexplained bleeding or discharge from the body
  • A strong odor that you can’t explain (can be described as smelling sick)

The Most Common Types of Cancers in Dogs

There are countless forms of cancer in dogs, but we’ll go over some of the most common types of cancer found in dogs. This can give you a clearer understanding of how these cancers work and the way in which they might affect your dog. Hopefully, the list below is able to clear things up for you and help you spot possible signs of cancer in your dog, especially as your dog gets older.


Canine Lymphoma

This is the most common form of cancer in dogs, and it doesn’t refer to just one type of cancer. It is actually a term coined by veterinary professionals to describe a group of cancers that stem from lymphocytes - white blood cells that help the body fight infections. This means that there are over 30 different forms of lymphoma that dogs can develop.

However, the most common types of lymphoma tend to be alimentary, multicentric, mediastinal, and extranodal. Often, the signs can be very mild in dogs, and they only become severe when the cancer starts to affect the organs. The most noticeable sign is lumps in the neck, which is where the lymph nodes have started swelling.


This cancer in dogs affects the bones, and it is the most painful form of bone cancer. Usually, it is found in the largest or longest bones in a dog’s body, which means the legs and pelvis are the most frequently affected. Any breed of dog can contract this form of cancer, but it is more commonly seen in larger breeds because of the size of their bones.

Lameness and pain are usually the first signs you will notice, and swelling will become more noticeable as the tumor grows. The bone usually becomes weaker as the cancer progresses, which is why so many cases are first brought to vets because of a fracture or break in the bone. Treatment is still undergoing trial studies, but there are promising results so far.

Transitional Cell Carcinoma

This cancer in dogs tends to form in the urinary tract, and it is certainly the most common form of cancer in that area of the body. It can form in any part of the urinary system, but the most frequent area is near the kidneys. Treatment for this form of cancer usually includes surgery, but radiotherapy and chemotherapy are also common options.

Mast Cell Tumor

This form of cancer in dogs is most commonly found under or on the skin, but there have been cases where the masses have been seen under the eyes, around the mouth, along the spine, and in the throat. It is a very curable form of cancer if detected early, but the tumors can be quite difficult for vets to remove - especially if they are in the throat.

Alongside lymphoma, this is considered the most common form of cancer in dogs. The malignancy of the tumor will be graded after examination, and this helps vets to determine how likely they are to spread and what the best form of treatment will be. For low-grade tumors, surgery is likely to be the only thing needed, and higher grades may need chemotherapy.


This cancer in dogs is slow to spread, but it is also very difficult to treat and can be challenging for veterinary professionals to tackle. It is usually found on the legs and feet, and while radiotherapy is often an option for treatment, amputation tends to be the most common way forward to help stop the spread and remove the affected area.

Canine Melanoma (Skin Cancer)

These tumors are found on the skin, and it is a common cancer in dogs (just like in humans). Most of the time, melanoma tumors are benign, which means they are not dangerous and can be treated by removing the mass. However, when the tumor is malignant it becomes very serious because it can spread so rapidly to other parts of the body.

Usually, you will find melanoma tumors around the feet or mouth (oral melanoma) of a dog, and they are usually dark in color (although not always) which can make them a little easier to detect. Even if you think the masses are benign, it is essential to get them checked quickly.


This cancer in dogs is common, but it is also one of the most serious and can be fatal if it is not treated with haste. The tumors are usually found in the spleen, and they tend to grow incredibly large. However, they can form anywhere in the body where there are blood vessels, and in addition to growing, they can rapidly spread to the other organs in the body.

The danger comes from the fact that the tumors are aggressive on a local level and have the ability to spread, which is why surgery and intervention are required as quickly as possible. Unfortunately, even with successful treatment, the long-term prognosis for dogs with this form of cancer is not great. Only 10% are likely to survive the year following remission.

Mammary Cancer

This form of cancer in dogs is most common in females, but it can also affect male dogs. Usually, this is more common in female dogs that were never spayed but there are certain breeds that could be more susceptible to this form of cancer - namely spaniels and dachshunds. Treatment tends to be straightforward, with surgery as the primary option and then the potential for chemotherapy if needed afterward.

To Conclude

A diagnosis of cancer in dogs is difficult for us to accept, especially in creatures that have so much unconditional love to give. It can seem deeply unfair, but the chances of successful treatment increase when you catch the signs early. Through this guide, I hope I have been able to help you learn more about canine cancer so that you can keep an eye out for your furry friend.

Want help preventing cancer for your dog? A DNA test for dogs from CirclePaw can help you learn which (if any) types of cancer your dog has a higher risk of developing, due to your dog’s DNA. This DNA test for dogs gives you insight into your dog’s genetic makeup, revealing health conditions, diseases and cancers they might have a genetic predisposition to. Being armed with this information about your dog can help you stay prepared and ensure you’re watching out for any of the symptoms. Your dog’s health is important, and these DNA insights can help you stay on top of it.


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