12 Signs Your Dog May Have Cancer

12 Signs Your Dog May Have Cancer

The sad truth is that 1 in 3 dogs will get some type of cancer in their lives. However, when caught early, around half of all canine cancers are treatable. 

Many conditions can cause symptoms similar to certain types of cancer in dogs. Spotting those symptoms is an important step, and getting an accurate diagnosis from your vet is always going to give your pet the best chance of recovery. 

Read on to find out about the most common types of cancer in dogs and learn about the 12 signs your dog may have one of them.

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Common Kinds of Cancer in Dogs

Cancer happens as the result of the uncontrolled growth of cells in the body’s tissues. If not stopped in its tracks, it can spread either locally around the primary tumor, or distantly to other locations or organs. Here are some of the most common types of cancer in dogs:


This type of cancer is a tumor of the cells that line blood vessels. It tends to affect middle-aged or older dogs the most. Particular breeds such as Golden Retrievers and German Shepherds are more prone to it. It is most commonly found in the spleen.

Mast Cell Tumor

Mast cells are a type of white blood cell that are found in many forms of connective tissue within the body. They typically form tumors (of varying appearance) on the skin, but are able to spread to distant locations and organs. Approximately 1 in 5 dogs will develop a mast cell tumor at some point in their life, with Boxers being especially at risk.


The most common signs of lymphoma are swollen lymph nodes under the neck, shoulders, or behind the knee. This type of dog cancer is typically treatable if caught early. Golden Retrievers, Standard Poodles, and Australian Shepherds are more prone to it.


This type of dog cancer is the most common bone cancer in dogs. Generally it appears in limb-bones, but can also appear in the areas such as the skull, spine, and ribs. It tends to affect older, large or giant breed dogs. 

Brain Tumors

Epileptic-like seizures or other severe behavioral changes are clinical signs of brain tumors in dogs. Sometimes surgery is possible but chemotherapy and radiation therapy can control some inoperable tumors.

Bladder Cancer

A dog may not display signs of this slow-developing dog cancer for several months. Bleeding and difficult urinating are common symptoms.

Mammary Carcinoma

A type of breast cancer in dogs, non-spayed female dogs are at higher risk for developing malignant mammary tumors. They generally appear as hard, mobile lumps in the tissue of the teats.

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Squamous Cell Carcinoma (SCC)

You’re most likely to see this in the mouth and the nail beds of the toes. SCCs of the tonsil and tongue can be aggressive, and difficult to treat. 


This type of cancer often happens in dogs with dark skin. You might typically notice small, dark lumps, but they can also appear as big, flat, wrinkled masses. Like skin cancers in humans, early surgical removal is often the best choice.

Testicular cancer

This type of dog cancer is common in unneutered dogs. It is often curable with surgery if caught early.

12 Signs of Cancer in Dogs to Watch For

There’s a wide range of cancer types, affecting nearly any part of the body, and all with a variety of different symptoms. It would be impossible to list all the specific signs, but some do appear more than others. The best advice is to consult a vet if you witness any of these symptoms:

  1. Unexplained Lumps and Bumps

Several types of cancer can cause masses anywhere on your dog’s body. You should regularly check for unusual lumps and bumps on your pet, and if you notice anything – get it checked by a vet.

  1. Inflammation in the Nipple Area 

This could be an indication of a mammary gland tumor. One or more nodules in the nipple area can get inflamed and swollen. Malignant mammary tumors can spread to lymph nodes and the mammary glands themselves if untreated.

  1. Abnormal odors 

Changes (generally for the worse) in the various smells of the dog could the sign of a malignant process going on. This could include examples such as particularly bad breath or abnormally bad smell from around the anal region. If your dog is smelling worse than usual and you don’t really know why, the safest option is to get it checked by a vet.

  1. Lameness

This could be an indication of osteosarcoma or other bone cancer in dogs. This bone cancer grows rapidly and often spreads to other areas of the body. Dogs with osteosarcoma may display signs of pain and walk with a limp. Affected limbs can appear swollen as well.

  1. Pigmented Sores

Darkly colored sores may be a sign of melanoma. They tend to affect the lips and mouth but you might also see them on your dog’s nail beds, foot-pads, and eyes.

  1. Swollen Lymph Nodes

Several kinds of cancer can lead to lymph nodes feeling more prominent. You may notice swollen lymph nodes in the knee, neck, and armpit areas in the first instance.

Lymphomas (as the name suggests) common cause enlarged lymph nodes. A variety of canine cancers can also spread locally to nearby lymph nodes, causing them to grow in size. These include mammary gland tumors, melanomas, and osteosarcomas.

  1. Wounds That Won’t Heal

The mast cell tumor is an especially aggressive kind of cancer presenting as a skin lesion that simply won’t get better. Abnormal growth of these cells leads to the  uncontrolled release of histamine. This irritates the region around the tumor, interrupting the normal healing process of a wound.

  1. Stomach Problems

As an example, the huge release of histamine connected to mast cell tumors can lead to severe issues with the gastrointestinal system. Stomach ulcers, vomiting, and diarrhea are not uncommon. Other local cancers of the gastrointestinal tract (such as the stomach, intestines, or colon) can also lead to chronic vomiting and diarrhea.

  1. Sudden Weakness or Collapse

Sudden collapse is a common symptom of hemangiosarcoma, cancer of the cells lining the blood vessels. This is normally due to internal bleeding related to a ruptured spleen. This is a medical emergency, and you must seek veterinary attention as soon as possible.

  1.  Labored Breathing

Many canine cancers mentioned are capable of spreading to the lungs. That in turn can lead to respiratory distress. And any cancer that is making your dog generally weak could also lead to more labored breathing.

  1. Unexplained Weight Loss

Weight loss can be a side effect of many cancer types, including osteosarcoma, hemangiosarcoma, and lymphoma. It often happens due to the metabolic demands of the tumor in combination with the cancer making the dog feel nauseous or otherwise unwell. If you dog seems to be losing weight – and you don’t know why – absolutely get checked by a vet.

  1. Lethargy

Similar to unexplained weight loss, if your dog seems to be getting more and more tired it could be the sign of something more sinister going on. Should this go on for a prolonged period of time, absolutely get a check-up at your local vet.

Book a Consultation Today!

Not all cancer-like symptoms will mean your dog has cancer. If you’ve noticed a sign that you think may mean your dog has cancer, your first port of call should be a vet.
Our team of highly experienced vets is on standby ready to talk to you. Book a timeslot today and get some expert advice.

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