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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Signs of Cancer in Dogs

Updated: June 30th, 2021


Many people ask me what to look for to tell if their dogs have cancer. I thought I should give you a little summary of some of the biggies.

Many people ask me what to look for to tell if their dogs have cancer.  Well, I must confess it is a tough question since there are so many cancers, and they all can present a little differently.  I thought I should give you a little summary of some of the biggies.

First, statistically, cancer TENDS to affect older dogs.  So, more lumps and bumps on a young dog are benign than cancerous.  One hallmark of a cancer is it worsens over time.  Cancers you can see usually get bigger. A growth that stays very small for years is not likely to be a true cancer.  Again, this is on average and is not a guarantee.

Some cancers are visible, while others are internal. The visible ones can be blackish (melanomas), purplish (hemangiosarcomas), fleshy, inflamed and red (histiocytomas), look like a non-healing open sore (squamous cell carcinomas), be firm, hard and deeply attached (fibrosarcomas), or have any appearance (mast cell tumor, the great imitator).

The internal ones are invisible, so we have to look for overall signs in the dog. When they are far along, cancers usually cause weight loss (cancer cachexia) without an obvious external reason. They often will cause less appetite.  Many times dog owners will tell me they think their dog got tired of his or her food.  They can cause low energy, where the dog will just lay around a lot.

NOTE: If you are reading this article and worried about your dog, do yourself and your dog a favor and get Dr. Dressler’s The Dog Cancer Survival Guide. It’s the best-selling animal health book for a good reason: it’s helped thousands and thousands of dogs just like yours face and cope — and even beat — cancer. And if you really want to help your dog, get the Dog Cancer Kit we put together for you, based on what’s been most helpful for other people who have faced this terrible illness.

-The Dog Cancer Vet Support Team

(The Team of Dog Lovers Behind This Site Who Understand What It Means to Have a Dog with Cancer)

Internal cancer signs also depend on where the cancer is happening. For example, a bone tumor (osteosarcoma) might cause a limp, or a bladder tumor (transitional cell carcinoma) might cause straining to urinate, blood in urine, or urinating small amounts frequently.  A tumor found in the wall of the stomach might cause vomiting, and in the intestine, diarrhea.

Some cancers cause internal bleeding, like hemangiosarcoma of the spleen.  This bleeding causes sudden weakness and wobbly legs.  A nasal tumor like a squamous cell carcinoma might cause discharge or bleeding from a nostril, or sneezing that won’t go away. Lung cancers (bronchial adenocarcima) or tumors of the heart can cause coughing. Lumps in the breast with discharge from teats could be mammary carcinomas.

The good news is, not all of these signs point to cancer.  Lots of other things can cause each and every one of these signs.  The important thing to remember is to get it checked out by someone who knows what they are doing.  If we are dealing with cancer, moving early is the way to go.

For more information on all the ways cancer can come about and what you can do, you will definitely want to read the Dog Cancer Suvival Guide.

Best to all,

Dr Dressler

Leave a Comment

  1. Christine Adamonis on April 16, 2019 at 8:05 am

    Hello, I found a small lump the size of a small pee on my Min pin/Chi she is about 5 on her shoulder area. I feed her a raw diet with Organic eggs organic treats and veggies, I don’t use any chemicals in my home everything is organic.

    • Dog Cancer Vet Team on April 16, 2019 at 8:12 am

      Hi Christine,

      Thanks for writing. As Dr. Sue writes in this article, if a lump is larger than 1cm, or has been there for longer than a month, get it checked ASAP. No one can tell you what it is just by looking at it or feeling it. Dr. Sue recommends that you get your vet to aspirate the lump as soon as possible so that you know what you’re dealing with 🙂

  2. leeanne twitchen on February 18, 2019 at 3:52 pm

    hi my dog has a big lump her side

    • Dog Cancer Vet Team on February 19, 2019 at 7:54 am


      Thanks for writing! As we’re not veterinarians here in customer support, we can’t offer you medical advice. However, we can provide you with information based off Dr. Sue’s writings 🙂

      As Dr. Sue writes in this article, if a lump is larger than 1cm, or has been there for over one month, get it checked by a veterinarian ASAP.

  3. Lori on September 14, 2018 at 9:35 am

    I am very concerned about my 10 year old cocker spaniel who had a large bump on the top of his head. This bump has grown over the past or so and is now about the size of a golf ball. The mass is located on the top portion of his head and is hard. It has grown so fast and large it’s hard to know what we are dealing with. When he scratches his head I believe it causes it to bleed. Any words of advice on how to handle this?

  4. stacey on September 2, 2018 at 5:15 am

    my dog has a lump at the lower left nipple, which started small and in just a few weeks it has grown larger. its warm and hard to touch and is moving in a line down towards the rear of the dog. i thought something was not right because she was drinking more water than usual and her appetite has increased to the point where shes snatching off dinner plates. she doesnt seem ill as shes still very active. she never had many periods as other female dogs and is around 8 years old. iam really worried as i lost her mum to cancer.

    • Dog Cancer Vet Team on September 6, 2018 at 9:01 am

      Hello Stacey, thanks for writing. Dr. Sue, one of the co-authors of the Dog Cancer Survival Guide, wrote this amazing article on when you should get your dog’s lumps checked. If she has had the lump for over one month, or if it is larger than 1cm, go to your veterinarian, and get the lump aspirated.

      Here’s the link to the article:

      We hope this helps! 🙂

  5. Lynda White on October 30, 2014 at 4:22 am

    I need help my very very loved pet is acting different like no energy she hurts and has a large mass on her leg. Can anyone help me please

    • Susan Kazara Harper on October 30, 2014 at 7:09 pm

      Lynda, You need to make an appt with your vet. These symptoms could mean something serious is going on, or maybe something manageable. But if you don’t get the diagnosis you are only worrying, and your dog is not feeling better. I know you don’t want her to keep hurting. Please make an appt soon so you can both feel better.

  6. jasmin on October 20, 2014 at 3:01 am

    I have a 13 year old staff shes got black like wort lumps and her stomach as just bloons crys alot

    • Susan Kazara Harper on October 22, 2014 at 6:57 pm

      Have you been to your vet? You need a diagnosis. Please get an appointment.

  7. Susan Kazara Harper on June 22, 2014 at 1:07 pm

    Karen, You need to get one vet who is either an oncologist or has a lot of experience with cancer. Are there multiple vets involved because there are different vets at the practice you go to? If so, I recommend you get in touch with that practice and ask for an appointment with the vet you have the most faith in. OR, go to a completely different practice and let them know all the symptoms, and all the treatments. The symptoms you describe are quite serious, and she is not going to get better without proper help. The bleeding and problems breathing are weakening her. Please don’t put it off. Make a call Monday morning and get her in for some help. I know it’s frustrating getting different answers. You’re the only one who can help her, and you do that by getting her to a vet and sticking with that person so he or she can follow your girl’s case. Good luck. We are all hoping for the best.

  8. Aphie on June 4, 2014 at 1:53 am

    Hey guys I need a little help here. Please help if possible. I’m 18 years old, working a minimum wage job, and received a Chihuahua from my friend about 3 months ago. I immediately fell in love with her. I’m still clueless as to how old she is but when she got to my house she was fat and now she barely eats anything but little bits and pieces of my food. She also has this huge red lump on her stomach and all she really does is sleep most of the day. I’m terrified. I already love this dog to death. Do you guys think it can be cancerous? As I mentioned earlier, I’m still only 18 with a job that can barely cover my cellphone bill, house necessities, etc. I can’t afford a vet. I really need help. Thank guys.

    • Susan Kazara Harper on June 4, 2014 at 4:03 am

      Hi Aphie,
      I can hear how much you love this little dog in your message. But there is so much more information I need to try to help. Could the lump be cancerous, yes, but also maybe not. Having a pet is expensive if you’re going to do right by them, and going forward you do need to figure out how to fit her in to your expenses. You’d feel terrible if your cell phone bill was paid but you had a emergency where she needed you to come through for her. I’m going to send you a separate email so we can check this out a little deeper, so please be on the look for it. Give your girl a cuddle from me,

  9. Nettie on May 13, 2014 at 7:56 am

    My jackrusselle is 13 years old has tremiors when sleeping and terrible bubbles coming out of his nose vet kepts putting him on meds and also loosing wait sleeps allay has to lean head down to breath

    • Susan Kazara Harper on May 13, 2014 at 9:15 am

      Hello Nettie,
      Well, something is surely not right with your little one. You haven’t said what meds your boy is on, but if you’re not clear about what your vet is treating, it’s time for direct questions. You can call the vet office and ask a nurse to help clear things up from your records. If your vet has not given you a diagnosis are you comfortable asking to consult with a different vet? There’s no way to make a guess on the internet. You’d be happier getting an idea of what’s going on and a treatment plan, and your dog will be happier as well. There is nothing wrong with asking for a second opinion, or going to another vet. He’s your dog my Dear. Do what you feel you must. Good luck to you both.

  10. Susan Kazara Harper on April 30, 2014 at 5:54 am

    Hello Kat,
    I apologize for the delay responding to you. We can’t say whether the bump on your dog’s nose could be cancer online. Just not possible without a vet’s exam. However, it is good news that it moves around and only in the skin. That’s a good sign but I urge you not to leave it at that. The fact that he’s skinny and doesn’t put on weight… no way to comment I’m afraid. So much information is not known. So here’s the bottom line. These blog posts would be good for you to look at; and and then if you make an appt with your vet, your dog can really be checked out for both the nasal bump and the weight situation. If you wait and worry, best case scenario is it turns out to be nothing, but you’ll be worrying. Worst case scenario is that this could be signs of a problem, and the longer you wait the worse the problem will be. In the meantime, regardless of the results, please do check into giving him the best nutrition with real food, which will help him stay healthier through his life. Please get him checked, Good luck and we’re all hoping for the best.

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