Dog Cancer: Signs, Diagnosis, and Treatment Options

This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS, with contributions from Dr. Debora Lichtenberg, VMD. Writer Melissa Smith also contributed. This article was last reviewed on July 13, 2024

Understanding Dog Cancer Concerns

When our pets are sick, our minds often trip into worst-case-scenario mode: Does my dog have cancer?

Despite all my training as a veterinarian, I did this, too, when one of my own dogs went lame. My mind immediately screamed, “He might have bone cancer!” rather than the more likely alternative that my dog was in a fight (which was the case).

Does My Dog Have Cancer?

When a dog isn’t well, vets often run blood tests.

When we say that test results are normal or negative, commonly the person will let out a breath and say, “So my dog doesn't have cancer.”

However, routine blood panels don’t diagnose cancer. They can provide clues, but that's often as far as screening tests go.

First, We Get a Medical History

It starts with gathering information about the dog with a history and a physical exam, paying particular attention to: General body condition Gum color Organ texture and size Skin lumps and bumps Unexplained changes in toilet habits

This helps build a general picture of the dog’s health and can suggest problems other than cancer that need investigating. The vet then uses this information to run specific tests and reach a diagnosis.

Blood Tests Don't Actually Look for Cancer

For many dogs with cancer, a routine blood test comes back normal. Why is this?

The test isn’t looking for cancer. It measures how well the organs function, electrolyte levels, and the size and number of red and white cells.

While blood cancers such as leukemia or some lymphomas can shift the white cell count, these are the exception rather than the rule.

Cancers often have a local effect that doesn’t show up in general blood tests.

The Purpose of Screening Tests

When a dog shows symptoms like weight loss or increased thirst, blood tests are essential to rule out common problems such as overactive thyroids, diabetes, or kidney disease.

When these tests don’t provide an answer, the suspicion of cancer rises. Here are two examples where cancer clues do show up in blood tests:

• Blood cancers: Too many of one type of blood cell are produced.
• Bone marrow cancer: Too few of certain blood cell types are produced.

My Dog Has a Lump

When there’s a skin lump present, taking a sample of cells for analysis is ideal. This could involve:

• Fine needle aspirate: A few cells are sucked up via a needle and syringe. This is noninvasive, doesn’t require an anesthetic, and gives a rapid diagnosis for some cancers.
• Biopsy: This is a surgical procedure to remove a small tissue sample. This requires sedation and local anesthetic.
• Excisional biopsy: This is where the surgeon removes the whole lump, which is sent for analysis.

Advances in Early Detection of Dog Cancer

Recent advancements in veterinary medicine have significantly improved the early detection of dog cancer. Techniques such as genomic testing and advanced imaging technologies are now available to identify cancer in its initial stages. These advancements allow veterinarians to detect dog cancer earlier than ever before, increasing the chances of successful treatment. Genomic Testing:

• What it does: Genomic tests can detect markers in the bloodstream that indicate rapid cell growth, a common sign of cancer.
• Benefits: This method helps identify cancers before they become symptomatic, allowing for earlier and more effective intervention.
• Advanced Imaging Technologies:
• Types: MRI, CT scans, and advanced ultrasound techniques.
• Benefits: These imaging tools provide detailed views of internal structures, helping vets locate and identify tumors that might not be detectable through physical exams or basic tests.
• A New Blood Test for Cancer in Dogs:
• Availability: In the United States, a new blood test can detect markers released when cells multiply too quickly, indicative of cancer.
• Limitations: While promising, this test is not perfect. It may miss slow-growing cancers and only provides a "yes-no-maybe" result, necessitating further imaging like X-rays or ultrasounds to confirm and locate the cancer.

Early detection through these methods means that interventions can be more targeted and effective, potentially leading to better outcomes for dogs diagnosed with cancer. If you’re concerned about your dog, consult your vet about these advanced diagnostic options to catch any potential issues early.

Early Warning Signs of Dog Cancer

It’s never a topic any of us like thinking about — the big “C,” cancer. Most of us have probably been touched by it in some way or another in our lives.

There are varying degrees and progressions of cancer, and early discovery with most cancers goes a long way toward a successful recovery. Here are some of the signs of cancer in a dog:

Suspicious Lumps or Bumps

When you’re engaged in playtime or just patting time, run your hands over your dog just to get the lay of the land.

If you encounter a lump that you haven’t felt or seen before, it’s probably not a bad idea to get it checked out by the vet. Chances are it’s nothing — but as they say, better safe than sorry.

Strange, Off-putting Odors

Every once in a while, your dog is going to let out some gas, and it is never pleasant.

But if you notice a persistent odor around the mouth, ears, or anal areas, it is time to get that checked out. Some cancers cause foul odors.

Unexplained Discharge

Pus, blood, or anything out of the ordinary should be looked into immediately. After all, blood comes from somewhere and if you can’t see where your dog is bleeding from, there may be internal bleeding.

Pus can signify an infection or may be a sign of something more serious.

Persistent Wounds

This could be a sign of an infection or skin disease, but it could also be cancer. Most superficial wounds heal within a week or so, but if your dog has a wound that just isn’t healing, get it checked out.

Unexplained Weight Changes

Sometimes your dog is just pudgy and you have to put them on a diet. It happens to a lot of us, but if your dog is losing weight and you haven’t changed the diet, that is something to look into.

Many cancers can cause dramatic weight loss in dogs.

Appetite Changes

Feeling ill can put many dogs off food, but a persistent disinterest in feeding time is something to ask your vet about. Another thing to watch for is increased thirst.

Coughing or Difficulty Breathing

As with the other signs on this list, it’s difficult to point at a symptom and say, “That’s cancer!” with any certainty.

Many things can cause coughing and/or breathing problems: Colds, kennel cough, and aspiration pneumonia are just a few illnesses that can cause this symptom.

However, some lung cancers and tumors can manifest in these symptoms. Difficult respiration should be cause for concern.

Sudden Lethargy or Depression

Dogs have feelings, and if they seem downcast day after day, there may be something going on inside them that you can’t see.

If they have cancer, a great deal of energy is being devoted inside to fighting the disease, and it can cause your dog to seem tired and not interested in doing much more than lying down or sleeping.

Unexplained and Persistent Changes in Bathroom Habits

A house-trained dog losing bowel or bladder control occasionally is somewhat common. Being inside too long, drinking too much water, or getting a stomach illness could be causes. Persistently losing control is another matter.

Constant and persistent diarrhea or constipation is a sign of ill health as well. Every animal eats something that doesn’t agree with them in their lifetime, of course — but when bowel or bladder control is lost or sudden stool or urine changes happen with no explanation, that’s definitely worth a mention to the vet.

Unexplained Pain

If your dog is limping, showing sensitivity toward a certain area of the body, or snapping at you when you go near, your dog may be in pain.

If your dog has pain and you can’t explain it, get it checked out by your vet just to be safe. The hardest thing about diagnosing cancer in a dog is that it manifests in symptoms that are so broad and across the spectrum.

You know your dog better than anyone else. Watch for obvious changes. Don’t be afraid to call your vet and ask for advice, a quick opinion, or for your dog to be seen.

How to Reduce the Risk of Cancer in Your Dog

What’s the hardest part of being a dog's human?

Most people will say it's the fear of their dog being unwell, or the fear of losing them.

Protecting our dog's health is what de-sexing, de-worming, and vaccinations are all about. But can we go further than that? Is there a way to protect our precious fur friends against cancer?

The answer is “Yes, maybe, but no guarantees.”

Causes of Cancer in Dogs

To prevent a problem, it’s helpful to recognize the risk factors. Family History and Inheritance

Some dog breeds carry a higher risk of cancer than others. This suggests a genetic link to cancer that is passed from susceptible parents to their pups. Unfortunately, this is difficult to prevent because the parents produced litters before they themselves became sick.

Examples of breeds at risk include:

• German Shepherds: They are prone to hemangiosarcoma. This is a tumor that affects highly vascular organs such as the spleen or heart.
• Boxers: Have you heard of the Boxer bump? This is the potentially serious skin cancer called mast cell tumors.
• Bernese Mountain Dogs: It is a sad fact that these beautiful, gentle giants have a high incidence of cancer.

Having one of these breeds does not automatically mean they’ll get cancer, but the odds are slightly higher. If you are "risk averse," then research the breed first to see what health problems might await.

Age
Getting older goes hand-in-paw with an increased risk of cancer.

It’s thought that an aging immune system is less efficient at policing cell mutations -- meaning instead of killing cancer cells, these mutations get a chance to become established.

The upside of this is that our dogs are indeed living longer.

Whereas we used to expect our dogs to die of renal or heart disease, modern drugs mean pets live longer -- allowing age-related problems such as cancer to show up.

Viruses
Certain viruses can increase the risk of cancer in dogs. For example, canine papillomavirus can lead to the development of warts and, in some cases, can progress to cancer.

Carcinogens and the Environment
Our pets are just as vulnerable to the harmful effects of carcinogens as people are. For example, pesticides, insecticides, air pollution, and asbestos can all make our pets ill.

Avoidance is best policy, which includes tobacco smoke that puts your pet at risk of lung cancer.

How to Reduce the Risk of Cancer in Your Dog

Enough of feeling helpless. Here are some concrete steps you can take to keep your dog well.

De-Sexing Dogs

• Female dogs spayed before their first season have a huge protection against mammary cancer in later life.
• For male dogs, neutering eliminates the risk of testicular cancer. However, current evidence is undecided with regard to protecting against prostate cancer.

A Healthy Diet

• Good nutrition helps feed the body’s immune system and strengthens its defenses.
• Antioxidants are particularly important as they eliminate damaging free radicals that cause cell mutations. Providing a vitamin E-rich diet to encourage the breakdown of free radicals is a sensible precaution.
• Being picky about the artificial preservatives, colors, and flavorings that go into your dog's mouth is a good way of reducing contact with edible carcinogens.

Reducing Identifiable Risks

• A white-coated dog with a pink nose is at risk of sunburn leading to skin cancer. This is because the dog lacks the protective pigment melanin.
• If you have a thin-coated or fair-skinned dog, keep them safe in the sun:

Vigilance and Vet Visits

• When detected early, most cancers stand a much better chance of treatment and cure.
• Check your dog's body over weekly. Be alert for new lumps and bumps.
• If you decide to wait, it’s essential to monitor things.

By following these steps, you can help reduce the risk of cancer in your dog and ensure early detection for better treatment outcomes.

Here's a veterinary oncologist's take on cancer in pets:

Signs Your Dog Should See the Vet

If your dog is diagnosed with cancer, especially when caught early, there’s a lot that can be done. The worst decision is to hope the problem goes away on its own and let precious time tick by.

At home, be alert for general signs of dog cancer, such as: A growing, changing, or angry-looking lump A swollen belly Difficulty breathing A lack of energy or appetite Increased thirst Lameness or stiffness

• A change in behavior, especially a lack of interest in walks or play

These are all indicators that your dog needs to see a vet. Prompt diagnosis can make all the difference.

While there is no guaranteed way to protect your dog against cancer, being proactive can help. Regular vet checkups, a healthy diet, and vigilance in monitoring your dog's health can make a significant difference.

Why Cancer Is Not a Death Sentence for Your Dog

If your veterinarian comes back into the exam room, after looking at an X-ray or an ultrasound, and utters the dreaded sentence, "I think your dog has cancer," many people would be devastated, and rightfully so.

However, just as in human medicine, there have been great advances in treating cancer in pets in the past few years. Although we may not be able to “cure” the cancer, it is possible that surgery, chemotherapy, or radiation—or some combination of them—can give your dog a great quality of life for many months or years to come.

Most cancers can go into remission. Some forms of cancer are, indeed, curable.

Chemotherapy

The word "chemotherapy" can be daunting for many pet owners. Common reactions include: “I couldn’t put her through that.” “I watched my mother die of cancer.” “It’s not fair to the dog.”

But consider the alternative. In many of these cases, if you choose to do nothing, your pet may be gone in a very short time. The goal of chemotherapy in pets is to prolong life while maintaining a good quality of life.

If my client's dog has a type of cancer that has a good chance of responding to treatment, I encourage them to explore the options. My aim is to keep those paws moving for as long as possible, ensuring the dog enjoys a good quality of life during treatment.

Benefits of Treatment

• Surgery can remove tumors and provide relief from symptoms.
• Radiation therapy targets specific areas to shrink tumors and alleviate pain.
• Chemotherapy can slow the progression of cancer and, in some cases, lead to remission.

Quality of Life

The primary focus is to ensure that your dog is not suffering. Modern veterinary oncology aims to balance effective cancer treatment with maintaining your dog's quality of life. Treatments are tailored to minimize side effects and maximize comfort.

By considering all available treatment options, you can make an informed decision that best suits your dog’s needs and circumstances.

In the video below, Mary K. Klein, DVM, DACVIM, DACVR, explains more about chemotherapy in dogs — and its side effects:

What Exactly Is Chemotherapy?

Chemotherapy involves drugs used to fight cancer, the schedule for administering those drugs, and the combination in which they are given, known as a chemotherapy protocol. In veterinary medicine, the aim is often to palliate the cancer and avoid harsh treatments that could cause suffering.

Common Concerns About Chemotherapy

“But the side effects are worse than the cancer.”

• This is outdated thinking. Veterinary chemotherapy protocols are designed to minimize side effects.
• If your dog has a bad reaction, the vet can stop, change drugs, lower the dose, or adjust the schedule.
• Owners play an active role in all decisions, so ask questions and consider pros and cons.

“If my dog goes on chemotherapy, she’ll lose her hair and be nauseous.”

• Veterinary chemo drugs do not typically cause hair loss. Breeds that do not shed, such as poodles, may experience a thinner hair coat, but they do not go bald.
• Some pets may experience mild gastrointestinal issues. If the reaction is severe, the drug can be discontinued.
• Most pets feel better within 1–2 days, experiencing mild anorexia or nausea. Occasionally, they need to come into the hospital for hydration and medication.
• “I can't afford that!”
• Treating some cancers can be very expensive, particularly at a referral center. Discuss options with your vet.
• Some chemo protocols are less expensive and can work well.
• If your vet is not comfortable administering chemotherapy, seek out other hospitals with a veterinarian interested in oncology.
• Remember, costs are spread out over many months, which can make the financial burden more manageable. Consider looking into pet insurance to help cover costs.

Types of Chemotherapy

Primary Chemotherapy

• Lymphoma (lymphosarcoma) is one of the most common forms of cancer in dogs and is highly responsive to chemotherapy alone.
• Numerous protocols and schedules are available based on factors such as cost, side effects, and vet visits.
• Before deciding not to treat, get all the information—you might be happily surprised.
• Chemo in Conjunction With Surgery
• Skin tumors, muscle growths, and mammary tumors (breast cancer) are common in dogs.
• The first line of treatment for these tumors is to surgically remove them.
• After surgery, chemotherapy can be used to prevent the tumor from returning, spreading (metastasis), or slowing progression.
• Based on the kind of tumor your dog has, which you will know from the biopsy results, your vet can offer treatment options.
• If there is a low risk of the tumor returning, you might take an “active surveillance” approach, monitoring your dog closely for any recurrence. This is similar to managing low-grade prostate cancer in men, where surgery may not be warranted.
• If the tumor is aggressive or “metastatic” (already in the lymph nodes), chemotherapy and/or radiation is recommended.

By understanding what chemotherapy involves and addressing common concerns, you can make informed decisions about your dog’s cancer treatment.

Common Types of Cancer in Dogs

Understanding the common types of dog cancer can help pet owners recognize the signs early and seek appropriate treatment. The most frequently diagnosed cancers in dogs include:

• Lymphoma: This cancer affects the lymphatic system and is highly responsive to chemotherapy.
• Mast Cell Tumors: Often appearing as skin lumps, these tumors can vary in severity and may require surgery or chemotherapy.
• Osteosarcoma: A type of bone cancer that is more common in large breed dogs. Treatment typically involves surgery and chemotherapy.
• Hemangiosarcoma: This cancer affects blood vessels and can be particularly aggressive. Early detection and treatment are crucial for improving outcomes.
• Melanoma: Commonly found in the mouth or on the skin, melanoma can be treated with surgery and immunotherapy.

By being aware of these common types of dog cancer, pet owners can be vigilant and seek veterinary care promptly if they notice any unusual symptoms in their dogs.

Get a Second Opinion

Information on cancer in pets is always changing and improving. Vets may have very different approaches and experiences in treating cancer.

• Seek a second opinion: If you are confused or just need more information, this is a good time to seek a second opinion.
• Consult a specialist: Consider consulting a board-certified veterinary oncologist or a local vet who has a special interest and experience in treating cancer.

Although we hope you never hear the bad news that your dog has cancer, the good news is that cancer treatment in pets is improving by leaps and bounds every day.

Frequently Asked Questions (FAQ)

References

• "Dogs and Cancer: Get the Facts." WebMD. https://www.webmd.com/pets/dogs/features/dogs-and-cancer-get-the-facts
• "Taking on Cancer." American Veterinary Medical Association. https://www.avma.org/resources/pet-owners/petcare/cancer-pets
• "Common Types of Cancer in Dogs." University of Wisconsin Veterinary Care. https://uwveterinarycare.wisc.edu/common-types-of-cancer-in-dogs/