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Signs of Cancer in Dogs: Warnings to Watch For

Sick dog lying on bed
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Cancer in dogs is something every pet parent worries about and it’s a diagnosis no veterinarian ever wants to give. Pet parents may look for signs of the disease and stress over every new lump, spot, or strange symptom.

The unfortunate reality is that almost anything can be a sign of cancer in dogs – including no signs at all. But, that doesn’t mean you should worry about every little thing. It means you should pay attention to your dog so that you notice changes and can monitor them appropriately. 

For every symptom of illness in a dog there is a list of potential health problems that may be the cause – ranging from mild to severe. Just because a symptom can be associated with cancer in dogs does not mean that it is cancer in dogs. 

While this article covers possible signs of cancer in dogs, it’s important not to jump to conclusions and to discuss your dog’s specific symptoms with your veterinarian.  

6 Types of Dog Cancer: Signs and Symptoms 

Before we discuss signs of cancer in dogs, it’s important to understand that our canine companions can develop different types of cancer – just like humans.

Each type of cancer may have different symptoms, often depending on the affected organ or location on the body. For example, dogs with lung cancer may cough while those with bone cancer may limp. 

The most common types of cancer in dogs are lymphoma (lymphosarcoma), bone cancer (osteosarcoma), soft tissue tumors (soft tissue sarcoma), and skin cancer (mast cell tumors). Other canine cancers with discrete symptoms include mammary cancer and bladder cancer. Here is more information about these types of dog cancer and some of the common signs associated with them:

Type of CancerWhat It IsCommon SignsBreed Predisposition
LymphomaCancer of the lymph nodes (immune system)Swollen lymph nodes under the chin, on the neck, behind the knees, in the armpits, or in the groinGolden Retrievers
OsteosarcomaCancer of the bonePain in a limb; swollen area of the limb; limpingRottweilers, other giant dog breeds
Soft Tissue SarcomaCancer of the muscle, connective tissue (ligaments and tendons), fat, blood vessels, and other tissues of the bodySwollen area on the body that is under the skin, may be painful on touching the area; limping; sudden collapseN/A
Mast Cell TumorsCancer of the skin that affects a cell involved in immune system function (most common)

Mast cell tumors can also develop in the stomach, spleen, intestines, lymph nodes, lungs, and other areas
Raised nodule on the skin that may be itchy or bleedBoxers, Pugs
Bladder CancerCancer of the bladderDifficulty urinating; pain urinating; dripping urine (incontinence); blood in urine; urinating more frequentlyN/A
Mammary CancerCancer of the mammary glandsFirm nodules associated with the mammary glands in dogs, may be very small to very largeN/A

There are many additional types of dog cancers that have more vague symptoms. For example, cancers of the stomach, intestines, or liver can look like intestinal upset with signs like nausea, decreased appetite, diarrhea, and vomiting. Cancer of the blood or bone marrow may cause tiredness that is mistaken for normal aging in dogs.

Lung cancer in dogs is more often due to the spread (metastasis) of other types of cancers. These are called secondary or metastatic tumors. Primary lung tumors are rare in dogs. Signs of tumors in the lung include coughing, decreased energy, difficulty breathing, decreased appetite, and weight loss. 

5 More General Signs of Cancer in Dogs

Dog with growth on leg

Cancer does what it wants – meaning cancer can cause just about any sign of illness. Even with specific types of cancer it can be hard to describe the most common signs because each dog is different and any sign of cancer is also a sign of several other less serious problems. 

Making canine cancer even more troublesome is that many dogs show no signs until the cancer is very advanced. At this time, dogs often display every sign of sickness at once. 

This is part of why your veterinarian recommends regular check-ups every 6 to 12 months. Veterinarians are trained to notice changes that pet parents don’t see. Some of this is based on a physical exam, while routine blood work can detect other hidden signs of cancer. Cancer caught early is always more treatable than cancer left undetected.

Some more general changes in your dog that could signal cancer and should always be evaluated by a veterinarian as soon as possible include:

  • Hard growths under the skin
  • Swollen lymph nodes (under chin, behind knees easiest places to notice)
  • Sudden onset cough in a senior or geriatric dog
  • A new skin growth that does not look like the others
  • Anything growing in the mouth 

Any lump that is bigger than 1cm (1/2 inch), is there for more than a month, grows, changes, bleeds, or doesn’t look or feel like the other lumps on your dog should be examined. It is always easier (safer, less painful, less expensive) to remove a small mass than a big one, especially on the limbs and face. Any growth that suddenly changes should be examined. 

What Should You Do If You See Cancer Symptoms in Dogs?

Dog at veterinarian getting an exam

It’s easy to start to spiral out of control if you suspect your dog may have cancer, but it’s important to keep one thing in mind – don’t panic.

The most important thing you can do is pay attention to changes in your dog. If your dog is just not acting like herself in any way, make an appointment with your veterinarian for a few days out (3-5 days or when your veterinarian has availability). If your dog is still showing signs at that point, take her in. If not, cancel the appointment at least 24 hours beforehand. 

Of course, if your dog worsens before the appointment, try to get an immediate appointment or go to an emergency clinic.

In addition to a comprehensive physical exam, common tests when there is concern for cancer include blood work, X-rays, ultrasound, and collecting samples of the possible mass (aspirate or biopsy). The tissue samples are then sent to a veterinary pathologist for evaluation and diagnosis. 

Your veterinarian will recommend tests based on your dog’s symptoms, history, and physical exam. Depending on her level of concern for cancer your veterinarian may recommend you see a veterinary oncologist. Oncologists are specialists at treating cancer. 

Many dog cancers are treatable. Some cancers can be surgically removed while others are treated with chemotherapy or radiation. Chemotherapy in dogs is much more gentle than chemotherapy in humans. 

In conclusion, always consult your veterinarian if you notice new symptoms or behaviors in your dog. Signs of cancer in dogs can mimic symptoms of many other conditions and health issues, and your dog’s veterinarian can diagnose and treat your pet appropriately. 

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