12 Signs Your Dog May Have Cancer: Don’t Ignore Them

12 signs your dog may have cancer

In this post we are going to be discussing all aspects of cancer in dogs, from how to know if your dog has it to the treatment options available. 


How common is cancer in dogs?

According to an article on the pets.webmd website called “Dogs and Cancer: Get the Facts”  cancer is responsible for about half of all deaths in dogs over the age of 10. There is some encouraging news as it seems half of those cancers are curable if caught early enough.

What causes cancer in dogs?

Advances in veterinary care and more involvement on the part of the pet parent means dogs are living longer, and we’re seeing them live to an age when cancers typically develop.

Other causes are thought to include

  • Genetics
  • Nutrition
  • Hormones
  • Viruses
  • Toxins

The truth is you may never know the exact cause. What is important is getting a diagnosis as quickly as possible, then discussing treatment options with your vet that will give your dog the best possible quality of life. 


12 signs your dog may have cancer2


Types of cancer

The Drake Center has published a list of the most common types of cancer, and rather than “re-inventing” the wheel, I am quoting directly from their site. 

Hemangiosarcoma: This form of dog cancer is an incurable tumor of cells that line blood vessels, called endothelial cells. Although dogs of any age and breed are susceptible to Hemangiosarcoma, it occurs more commonly in middle aged or elderly dogs. Also certain breeds have a much higher incidence including Golden Retrievers and German Shepherds. For this reason, we may recommend additional screening these breeds after age 5. This form of dog cancer develops slowly and is essentially painless, so clinical signs are usually not evident until the advanced stages when the tumors are resistant to most treatments. Less than 50% of treated dogs survive more than six months, and many die from severe internal bleeding before there is an opportunity to institute treatment.

Mast Cell Tumors: These are immune cells that are responsible for allergies. Mast cells can be found in all tissues of the body but typically form tumors on the skin in close to 20 percent in the canine population. They range from relatively benign to extremely aggressive. Certain breeds of dog are at an increased risk for the development of this tumor, indicating that genetics might be a cause. Boxers are especially prone to this type of cancer.

Lymphoma: This form of dog cancer can affect any dog of any breed at any age. Most of the time, it appears as swollen glands (lymph nodes) that can be seen or felt under the neck, in front of the shoulders, or behind the knee. Occasionally, lymphoma can affect lymph nodes that are not visible from outside the body, such as those inside the chest or in the abdomen. This can cause trouble breathing and digestive trouble. Generally this form of dog cancer is considered treatable if arrested in its early stages. Standard Poodles, Golden Retrievers and Aust shepherds are a few of the breeds with higher incidence of lymphoma.

Osteosarcoma: This form of dog cancer is the most common type of primary bone cancer in dogs, accounting for up to 85% of tumors that originate in the skeletal system. Although it mostly affects older large or giant breed dogs, it can affect dogs of any size or age. Osteosarcoma occurs in many areas, but it most commonly affects the bones bordering the shoulder, wrist and knee. A major symptom is lameness in the affected leg, or a swelling over the area that seems painful at the site.

Brain Tumors: Epileptic-like seizures or other extreme behavioral changes are usually the only clinical signs. CAT scanning and MRI is used to determine location, size and severity. Although some oral chemotherapy and radiation therapy can control some inoperable tumors, surgical intervention may be recommended if the tumor is operable.

Bladder Cancer: Some breeds are more at risk for this form of dog cancer than others. This is a slow developing dog cancer, and symptoms may not show for 3 to 6 months. Urinary obstruction and bleeding are common symptoms.

Mammary Carcinoma: Non-spayed female dogs are at high risk for developing malignant mammary tumors, but all female dogs regardless of reproductive state remain at risk. Approximately 50% of these tumors are malignant, and complete surgical removal is recommended if the cancer has not metastasized.

Malignant Histiocytosis: This dog cancer affects larger sport breeds most often. It occurs as localized lesions in the spleen, lymph nodes, lung, bone marrow, skin and subcutis, brain, and periarticular tissue of large appendicular (limb) joints. Histiocytic sarcomas can also occur as multiple lesions in single organs (especially spleen), and rapidly disseminate to involve multiple organs. Unfortunately there is no reported effective therapy for this form of dog cancer.

Squamous Cell Carcinomas: It is most often found in the mouth and the nail beds of the toes. Early detection and complete surgical removal is the most common treatment. Fewer than 20% of dogs develop metastatic disease. SCC of the tonsil and tongue are quite aggressive and fewer than 10% of dogs survive 1 year or longer despite treatment measures.

Mouth and Nose Cancer: This is a very common form of dog cancer, more so in the mouth than the nose. Symptoms include a mass on the gums, bleeding, odor, or difficulty eating. Since many swellings are malignant, early, aggressive treatment is essential. Cancer may also develop inside the nose of dogs. Bleeding from the nose, breathing difficulty, or facial swelling are symptoms that may indicate nose cancer.

Melanoma: This form of dog cancer most commonly occurs in canines with dark skin. Melanomas arise from pigment producing cells called melanocytes, which are responsible for coloring the skin. Melanomas can occur in areas of haired skin, where they usually form small, dark (brown to black) lumps, but can also appear as large, flat, wrinkled masses. Malignant melanoma, which develops in the mouth or in the distal limbs (usually the toenail beds), is an incurable disease. These tumors have very often spread to distant parts of the body by the time they are first noticed, making complete surgical removal impossible.

Testicular: This form of dog cancer is common in unneutered dogs with retained testes. This form of dog cancer is largely preventable with neutering, and curable with surgery if arrested early in the disease process.

Resource – Cancer Information – Dogs by Tumor Type

How do I know if it’s cancer?

Below you will find a list of 12 signs that might mean your dog has cancer. Is that definite? Absolutely not as many of those signs can also be symptoms of other illnesses. The only way to be certain is through testing at your vet’s office.

What this list does mean is that if your dog is exhibiting any of these symptoms, even in a minor way, you should schedule a vet appointment as quickly as possible.

In order to make your time as productive as possible –  

  • Make notes of your concerns
  • When did it/they first start
  • Has something different happened at home, while out on walks, change in food…
  • Take a video – trust me it can really help with a diagnosis

12 signs 

Lumps or bumps on or under the skin

Get into the habit of petting your dog (I know you already do, but this time you have an ulterior motive!!) and check for any lumps or bumps. This includes his face, ears…

Weight loss

Sudden weight loss in a dog whose diet and eating habits have not changed is a cause for concern.

Changes in appetite

Lack of interest in or difficulty eating does not necessarily signal cancer, but dogs (and cats) don’t stop eating without a reason so it is a sign of something. 

Unusual or offensive odours

Foul odours coming from anywhere on your dog’s body (mouth, ears, nose or anal region) can signal a tumour. Keep in mind, bad breath can be due to poor oral hygiene and ears because of an ear infection.

Pale gums

Knowing what your dog’s mouth looks like when he’s well means you will recognise changes. For example, pale gums could indicate blood loss, and cancer is one of the illnesses linked to this sign.

Lethargy/loss of stamina

There is a difference between a senior dog slowing down and true lethargy. Is he spending more time sleeping? Not as playful? Lost interest in walking? It could be arthritis for example, but combined with other signs can be worrying.

Changes in bathroom habits

Peeing more often, difficulty peeing or pooping, presence of blood, even accidents in the house. Peeing more often can also be a sign of kidney issues or diabetes, and accidents in the house could mean dementia

Open sores or wounds that don’t heal

Open sores or wounds that aren’t healing could be skin disease or infection, but….

Evidence of pain

Limping, lameness, stiffness when your dog walks, unwillingness or inability to jump on the couch like he used to and the like, are typically the result of arthritis, which is very common in senior dogs. However, there is also the possibility it is the result of cancer, especially bone cancer.

Respiratory problems/ difficulty breathing

Coughing, shortness of breath, general difficulty breathing can indicate heart disease as well as cancer.

Vomiting, diarrhea, bleeding or discharge

Vomiting, diarrhea, and/or bleeding and/or discharge from any part of your dog’s body needs to be checked out immediately.

Behaviour changes

Behaviour changes include some of the signs listed above, in addition to things like spending more time away from everyone, snapping, aggression. These behaviours can mean your dog is experiencing discomfort, or outright pain.



Signs your dog has cancer

How is cancer diagnosed

Your vet cannot say with any certainty just by looking or feeling whether or not a tumour is cancerous. Your vet may recommend blood work, x rays, ultrasound, MRI and/or biopsy. In the case of two of my cats who had growths it was a biopsy that confirmed their cancer diagnoses. 


The type of treatment, even whether or not to treat will depend on a variety of factors such as – 

Age of the dog

Overall health of the dog and his or her ability to tolerate the treatment

Tumour type – for example if it is slow growing, the drawbacks of treatment may outweigh any potential benefits

Has the tumour spread/the stage of the cancer

Finances of the parent(s)

Ethical considerations





Imunotherapy tumor vaccines which uses the immune system to stimulate the destruction of the cancer. Learn more in this article “Novel Cancer Vaccine Uses Animal’s Own Tumor Cells.”

Holistic/herbal therapies
Pain relief

A combination of one or more of the above

Treating cancer in dogs naturally

While researching natural treatment options I discovered plenty of recommendations for products such as CBD oil, Essiac Tea, The Kelmun Protocol (aluminum-free baking soda and grade B maple syrup) and various Chinese herbs. 

While I don’t have the knowledge or experience to comment, I can provide you with a few links so you can read up on the alternatives.

Natural Approaches for Preventing & Treating Cancer in Dogs and Cats

Holistic Vets Explain: Natural Treatment Of Cancer In Dogs

Holistic Cancer Prevention & Care in Your Pet


We all want to know “how long” but it’s virtually impossible to find out. Sure our vets can give us an educated guess, but how many stories do you hear of pets outliving that guess? 

Although I’ve never had a dog with cancer I did have 3 cats with different types of cancer. One lived for over 2 years with no treatment other than surgery, one lived an extra 7 months with chemotherapy and unfortunately we had no idea our third cat had it. My neighbour has a dog who was diagnosed with cancer over a year ago, and the odds were no better with treatment so they decided to just let him live a good life…until it wasn’t good anymore. He has survived longer than the year they gave him so you just never know.

The best thing you can do is enjoy every day, make his or her life wonderful and take lots of pictures!!

How to reduce the risk of cancer 

In the article “5 Ways to Keep Your Dog Cancer-Free for Life” Dr Karen Becker discusses her views on how to reduce the risk of your dog getting cancer. 

  • Keep your dog at a healthy weight
  • Feed an anti-inflammatory diet (real whole foods, preferably raw)
  • Reduce or eliminate exposure to toxins 
  • Don’t spay or neuter until 18 months-2 years (think about the risk of pregnancy and contributing to the over population problem, not to mention the possible contribution to behaviour problems by waiting so long)
  • Don’t over vaccinate

12 signs your dog may have cancer – conclusion

Lots of information you’re probably feeling a bit overwhelmed. Try not to panic and take things one step at a time. If you’ve noticed changes in your dog, even if it’s just something that seems “off” book a vet appointment sooner rather later. The quicker you find out what’s going on, the greater the likelihood of a better outcome.


Does your dog have cancer? What signs did you see that had you concerned? How was it diagnosed? What treatment was recommended? Sharing helps others so please leave your comments in the section below.


**I would like to invite you to join Senior Dog Care Club, my Facebook group for senior dog parents. It is a wonderful community where you will find lots of helpful tips and advice, a place to ask questions and share experiences. I look forward to welcoming you.**






  1. andrea

    It’s true.the best thing when we see some anomalies is to wait for something to happen, action sometimes may save our pet’s life. I have a routine to cuddle my pets very often and check them, I also am very careful in their diet,as i found out a lot of cheap industrial dog\cat foods often a cause of cancer.
    Thank you for the article

    1. Hindy Pearson (Post author)

      Hi Andrea, thanks for taking the time to leave a comment. It’s a good idea that you check your pets often. I never would have found that lump in my cat’s neck if I hadn’t been petting him. You’re right about your pet food concerns – there are lots of articles citing studies that have proven the link between poor quality pet food and all kinds of illness and disease.

  2. Elizabeth Haran

    Very good topic. My daughter has a wonderful Australian shep/lab mix. Sadie was found in a homeless shelter for dogs when she was about 1-year-old by my daughter who was looking for a small apartment lap dog. She took one look at Sadie and fell in love. Sadie was a puppy mill puppy and developed some pretty serious health issues now that she is in her later years. She is the most loving and caring animal I have ever known. I have some arthritis and so I tend to fall behind when my daughter, her daughter and my -son-in-law go for walks. Though Sadie can keep up with them, she always volunteers to stay behind and accompany me to the end of the trail. No one tells her to. She just knows that is what she should do. Love her, love her, love her. I guess what I am saying is, if anyone is afraid to take a puppy mill puppy because of health issues later in life, it is a factor, but there is nothing that can prepare you for the love that these beautiful little creatures can and impart. Thanks for your blog and for reminding us to watch our pets carefully.

    1. Hindy Pearson (Post author)

      Hi Elizabeth, thanks for sharing, and few things make me happier than hearing rescue stories. My husband and I rescued a puppy mill dog. She was kept in a chicken coop, breeding for 8 years. The shelter staff said they had never encountered such a terrible case. She would pee if you looked at her. Sadly we only had her 9 months before she died from what I believe to be veterinary incompetence. Thankfully in the time she knew love, and started to trust me enough to finally pet her after 7 months. I wish people would care enough like your daughter did, to adopt a homeless animal. People don’t realise they’re most likely buying a puppy mill dog when they choose to shop instead of adopt.

  3. Andre Kish

    Hello Hindy.

    A few days ago a good friend discovered her little pooch has got a disease similar to cancer with quite a few of the symptoms you mention here. Sadly, nothing can be done for her dog which is only 5 years old and may, at a push, last 1 or 2 years more.

    Because she checks her dog regularly she had previously mentioned these symptoms to her vet here in the UK but was told they could just be a short term infection. It was on the second check-up 3 months later, 4 days ago, she got the bad news.

    Now she has to make a decision as to whether to keep her pooch alive in the best state of health then let him go, or whether to extend life by a couple of very uncomfortable months due to serious side effects that would make the dog’s life nasty for him.

    May I ask you opinion here, as you have obvious unwell-dog experience?

    Many thanks – Andre

    1. Hindy Pearson (Post author)

      Hi Andre, what a sad situation for your friend to find herself in. I can relate. You say he may be okay for another year or two, but then you mention treatment extending his life by a couple of months. It’s not quite clear. It’s true, I do have lots of unwell dog and cat experience, but it would not be my place to offer an opinion on what your friend should, and should not, do. First let me say I hope she has a vet she trusts. If she doesn’t, she may want to find one and get another opinion. I’ve had two different vets (I live in England as well) responsible for the death of 2 different dogs, so I recommend she make that a priority. She needs to have this conversation with him, and be clear on what life would be like for her dog, with and without treatment. Like I said, it isn’t my place to offer an opinion, but personally I always consider what’s best for my animal, not for me. I also rely a lot on the opinion of my vet. I hope she finds the answers she needs.

  4. Lindsay

    Some great advice and things to look for in both cats and dogs.
    My question to you, how did you come to do training in Toronto? Did you live here at one time? I’m just outside of Toronto, which is why I’m curious.

    A pleasure to meet your acquaintance, I’m going to add you to my feed of blogs to read. 🙂

    1. Hindy Pearson (Post author)

      Hi Lindsay, thanks for stopping by, it’s a pleasure to meet you as well. I hope you enjoy my blogs!

  5. Ava Channing

    Dog cancer is so scary! I worry about it all the time. 🙁

    The issue is the warnings signs are also all caused by relatively harmless issues – so it could be cancer, but chances are if your dog has a change in apptetite for example – it’s probably something else. It would be nice if Doctors could tell us “in 9 / 75 cases, the loss of apptetite was cancer” so we can get a range of how scared we should be.

    1. Hindy Pearson (Post author)

      My best advice is for you to stop worrying and start enjoying life with your dog. Even if a vet knew for sure how many cases meant cancer, it still wouldn’t be relevant because you have no way of knowing if your dog is in that statistic. Feed him well, make sure he gets exercise and mental stimulation and take him to the vet when something seems “off.” That’s the best you can do and that’s all anyone can expect.

  6. Sadie

    It’s scary how many types of cancer there are! Thank you for sharing the signs so we can be aware of such changes in behavior etc. Two of my friends have had to treat their dogs for cancer. Sadly, one of the dogs passed.

    1. Hindy Pearson (Post author)

      It certainly is scary. I always encourage everyone to see their vet when they notice even the slightest change in their pet. I’m sorry about your friend’s dog, I know how sad that kind of loss is.

  7. Amy Shojai, CABC

    Cancer …ugh. Hate it. I’ve friends who are survivors, some who have succumbed and lucky folks who survived — and pets are no different. Thanks for the great information.

    1. Hindy Pearson (Post author)

      It’s incredible how one word can cause so much fear and heartache.

  8. Kamira

    Great informative and detailed post. I was shocked to learn 50% of dogs die of cancer over the age of 10 years old! Wow. This is very alarming to me to see the Big C so prevalent in humans and our pets. You offer great tips to help pet parents identify the signs. I never owned a dog however many of the symptoms you mentioned like lethargy, bad breath, vomiting and changes in appetite were all signs I noticed before my cat Dusty (deceased) passed away. She was diagnosed with thyroid cancer. The best defense we can have is being aware of our pets routine, informed and educated and feed our pets the best quality diet we can afford. Additionally, having a vet who is knowledgeable and compassionate helps too.

    1. Hindy Pearson (Post author)

      Thanks Kamira and I find it a shocking statistic as well. I agree the signs would be similar in cats and dogs. I like what you say about the best defense we have, and a vet who sees value in older animals is so important as well.

  9. Ruth Epstein

    I watch Layla carefully and have her checked twice a year. Thank goodness she is healthy and having done her DNA they found that she has no genetic diseases so am relieved with that one. Great post

    1. Hindy Pearson (Post author)

      You must feel so relieved! I was curious to do a DNA test on Red, but just by looking at her I was sure she was Chihuahua/Min Pin with the stripe of a Rhodesian Ridgeback. My husband never believed that last part so I wanted to prove him wrong!

  10. Emilia

    Cancer is a scourge – cat, dog, human, it’s a horrible thing. I hope an answer is found soon.

    1. Hindy Pearson (Post author)

      You are right, just the word is frightening.

  11. Kelly

    Several years ago I found a lump in Edie’s nose folds and all sorts of things ran through my mind – none of them good. I had her checked out right away and it was decided to remove the lump and have it tested. Those were the longest days waiting for the results! Fortunately, the cyst was benign. All I can say is whenever you find a lump, bump or cyst on your pet, the best thing to do is have it checked out right away.

    1. Hindy Pearson (Post author)

      Glad to hear Edie was fine, and I agree with you. Better to have something looked at right away then ignore it and have it become an even bigger problem later on. I know what it’s like waiting for test results, it can seem like an eternity.

  12. Heather Wallace, The Timid Rider

    A very thorough guide for a pet owner with questions. I work closely with two veterinary oncologists and am a board member for The Brodie Fund which provides grants to families struggling to fund their pet’s cancer treatments. There are so many moving parts and every pet and every case is distinct.

    1. Hindy Pearson (Post author)

      Wow that’s incredible Heather, it must be so rewarding. Vet care is so expensive and sadly out of my peoples’ reach. It’s nice to read about the various foundations helping cover treatment costs. It’s incomprehensible to have to let a much loved family member go because of money, yet that is the sad reality.

  13. Talent Hounds

    Our beautiful lab Cookie got cancer (tumours in abdomen) suddenly at 13 and eventually we helped her over the bridge as she was incontinent and had hip issues and arthritis too so constant pain and limited quality of life compared to how amazing she was for 13 years. Have had several friends’ dogs and my Mom get lymphoma so that is an ugly threat hanging over us all. Medications can buy time but are brutal and expensive. I have done quite a bit of research on lymphoma. Thanks for sharing your info.

    1. Hindy Pearson (Post author)

      I’m sorry to hear, it really is something that seems to hang over our heads, the C word. I do believe that just because there are treatment options for various conditions, it isn’t always the ethical and humane route to take.

  14. Cathy Armato

    This is such a great post, thank you Hindy. I shared widely so others can benefit from it. Thinking about cancer in any of my pets is so frightening, I can’t even bare it! This is very thorough information that will serve as a great resource.
    Love & Biscuits,
    Dogs Luv Us and We Luv Them

    1. Hindy Pearson (Post author)

      Thank you Cathy and thanks for sharing. It is very frightening but to be honest I never think about it. I had so many other things to worry about with Red, I didn’t give myself extra things to think about. I just hope it encourages everyone to speak to their vet when they see a change, even if it seems minor to them.

  15. Lola The Rescued Cat

    This is such an informative post. A cancer diagnosis is such a scary thing for a pet parent to hear. So many of Lola and Lexy’s friends have died from this tragic disease and it saddens us.

    1. Hindy Pearson (Post author)

      It is so scary, and I’m sorry to hear your kitties have lots friends to it. My dogs have never had cancer but I had 3 cats who did, each one a different type.

  16. Beth

    Thanks for sharing a list of possible symptoms! Early detection can make a huge difference when it comes to some cancers.

    1. Hindy Pearson (Post author)

      I’m always harping on about early detection, and the importance of speaking to your vet about any changes no matter how slight. A condition caught early increases the chance of a positive outcome.

  17. Dorothy "FiveSibesMom"

    My mother had breast cancer…my beautiful Gibson had hemangiosarcoma from which he passed from…the big “C” is so dastardly. Scary. Excellent article, Hindy. Pinning to share for awareness.

    1. Hindy Pearson (Post author)

      I’m so sorry about your mom and of course your special pup Gibson. One of my cats died from hemangiosarcoma. Thanks for pinning!

  18. Jana Rade

    The main problem with symptoms is that for the most part one cannot tell what is behind them because there are many possibilities, That’s why guessing and assumptions don’t lead to anywhere.

    1. Hindy Pearson (Post author)

      Absolutely true! It’s a complete waste of time, sometimes precious time, when people try and guess what’s going on. Make an appointment and get to the bottom of it as quickly as possible so treatment can begin while there is, hopefully, still something to be done.

  19. Sweet Purrfections

    I had no idea cancer was so prevalent in dogs and cats until the last several years. I guess more dogs and cats are living longer because she live indoors, so we are more aware of what is happening to them. The sad thing is there is much less research on feline cancer than canine cancer.

    1. Hindy Pearson (Post author)

      I think because our animals are living longer we’re seeing more diseases than we have before. I had 3 cats with different types of cancers. One we treated with chemo because surgery wasn’t an option due to the tumour’s location. He did very well on it, no adverse effects and he probably lived about 6 months longer than he would have without it. I do remember not being happy with the first oncologist we saw, she kept pushing another new drug and another, and when we refused made us feel we were the worst pet parents ever so we switched. I do believe just because there is something to be done, that does not mean it is morally and ethically right to do so in every case.

  20. Wanda

    Or there can be no signs…I lost 2 dogs…one had cancer of the liver…he let me know 5 days before he died…and we are owners that had our guy to a doctor stat if there was an issue. Our animals come first in everything we do. Losing him was devastating….i thought I would die. Miss him so much…

    1. Hindy Pearson (Post author)

      It’s true, sometimes there isn’t anything obvious. I understand how devastating the loss of a much loved companion can be. The heartbreak is the same whether we see it coming or not, but having it happen so suddenly is such a shock. I find creating a memorial or doing something to honour their memory helps.

  21. Wanda

    Hindy, you are so right on that point…my second dog a female had a grocery list of issues…we watched her through her ups and downs for 7 years and we saw scores of doctors. When the end came…it was just as hard..you always say, no more…i just can’t take this again…but you know what…you do it. We rescued 2 very needy animals..( or maybe we were the needy ones?) but they are just the best…they have the best personalities…love to travel and keep my husband and me busy…we are so blessed.We always tell others that we are the lucky ones!!!
    Have a great weekend.

    1. Hindy Pearson (Post author)

      I’ve never said no more as hard as it is to let them go, I can’t imagine life without a four legged creature in it!! Those 2 pups are lucky and it’s great to hear how they have fit right into your life and made it so fulfilling.

  22. Wanda

    Thank you…we have been very blessed…we have let go of the past ..its over, and we are looking at the future. These 2 girls, coming from the backgrounds they came from deserve the best of everything…and we work daily to give it to them. They are so grateful for that second chance….and we are honored to give it to them.
    Have a great holiday season…

    1. Hindy Pearson (Post author)

      I know how hard it can be to let the past go, but it’s wonderful you’re able to look with hope to the future. Your girls are lucky and I hope you all have a wonderful holiday.


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