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

My Dog is Acting Fine … And Got Diagnosed With Cancer?!?

Updated: July 27th, 2021


If your dog is acting fine, even though she has cancer, there could be a couple of reasons. Read this article to discover what they are.

How is it possible that our dog is acting fine — no signs of disease — and have cancer?

This is a pretty common question. It’s also a common scenario.  MANY dog lovers have gone to the vet to have a lump checked out, something that doesn’t seem to bother their dog. And then, sometimes even on the same day, the news arrives: cancer.

Whether this is a mast cell tumor, osteosarcoma, lymphosarcoma or some other kind of cancer, the news is horrific.  There is not much that can truly prepare someone for the shock.

Blam: your dog is acting fine … but has cancer.

In their shock, many clients and readers ask: how did this happen?

My Dog Is Acting Fine. How On Earth Could He Be Sick?

It is very natural that this question arises.

If my veterinarian is saying that my dog has cancer, how did this happen?

Aren’t cancer patients sick?

Shouldn’t there be some other sign if it really is as bad as the vet is saying?

The answer is no, not necessarily.  The key, in part, is in looking back to the natural world.

It’s In Their Nature

Here’s why: in nature, it is not helpful for animals to act sick.

Sick animals get eaten because they stand out from the pack.  Sick animals attract the attention of predators.

Another reason acting sick in the wild is detrimental is that a dog could lose its pack position.  To maintain their status among peers, it is better to be healthy and vigorous.  Those acting sick lose status.  Thus they have a strong social penalty for acting ill.

It becomes clear that showing signs of sickness can make matters worse for a dog in the wild.  There is a strong instinctive drive hide illness.

Get a copy of the Dog Cancer Survival Guide to read more on canine cancer

What Works In Nature Doesn’t Work in Domesticity

This instinct creates a problem when our canine companions are in need of medical attention.  Driven by this strong natural tendency, dogs hide their physical problems from those responsible for them: us!

Many medical problems (not just cancer) are kept under wraps, masked from caring dog guardians.

… Or Maybe There Are No Symptoms Yet

There is another reason dogs can act as if nothing is wrong while there is a cancer brewing.  Maybe a dog has a malignant tumor, but it has not spread enough to cause really significant tissue injury.

You may know a human who found a lump, and it turned out to be cancer, even though they were otherwise healthy. They didn’t know the lump was malignant, because it didn’t cause pain.

Tissue injury is what causes pain, and some tumors just don’t cause enough injury as they brew and progress. Until they do, both humans and dogs with cancer can act normally.

Decompensation = Problems Become Clear

Cancer usually starts as just a few old, deranged cells piling up. They should have already been replaced by healthy, vital cells by a process called apoptosis.  But cancer suppresses apoptosis (it’s one of the hallmarks of all cancers). No apoptosis = cells live forever.

No apoptosis = cells live forever.

If there is an apoptosis deficiency in the body, these cells will accumulate.

Meanwhile, the normal healthy cells continue to support your dog’s body, and your dog is acting fine.

This continues until those healthy cells can’t keep up.

Once the effect of the pile of deranged cells tips the scale, we see the problem.

This tipping point is called decompensation, a fundamental phenomenon in health and disease.

There is an in-depth discussion of cancer development in several chapters in my book. You may also be interested in reading chapter 3, for free, here.

Best to all,

Dr D

Leave a Comment

  1. Lily Madaffari on March 15, 2022 at 2:17 pm

    This article really helped make sense of things for me.
    3 weeks ago I took my 4-year-old Malamute in for a routine dental cleaning. She was as fit as a fiddle, just had a bit of stinky breath. When I went to pick her up, they put me in a room and told me the doctor would like to speak with me. I knew this was not their normal operating procedure and I sat there wondering what could possibly have gone wrong in a dental cleaning.
    The doctor came in and dropped the news like an atomic bomb: tumors, big tumors, lots of them, cancer. My world was rocked and we had to schedule another appointment for me to get the necessary information because the rest of that appointment is just a fog in my head.
    Our doctor says it’s squamous cell carcinoma, advanced stages with tumors on her tongue, jawbone and throat. He says there are no treatments that can help her. He estimates that she might live 2 months, and half of that time is already gone. But she seems perfectly fine. She is more restful than usual, but nothing extreme. The only really extreme difference is that one of the subordinate female dogs has all of a sudden tried attacking her ( that’s my biggest red flag.)
    Can a veterinarian really diagnose this condition without any tests? Just visual examination? Is it possible that the diagnosis could be incorrect?

    • Molly Jacobson on March 16, 2022 at 12:39 pm

      Only about 5% of oral tumors are benign, so your vet is probably pretty confident due to how much they found. Typically a biopsy is needed to see what type of tumor it is, so you might want to ask how they know it’s SCC, whether they did a fine needle aspirate or a biopsy. The chapter on oral cancer in Dr. Dressler’s book may help you to understand the prognosis a little better. Remember that dates like “two months” are based on studies where a (often small) group of dogs with a similar diagnosis were tracked. Two months is PROBABLY the median survival time — which means that in a study, half the dogs were still alive after two months, and half had passed on. It doesn’t mean your dog “has two months” as much as that’s a guideline. If your dog is still alive at two months, no one knows how much longer she will live. My guess is that her young age and how extensive the tumors are, and where they are, is what is giving your vet that guess. I would think about doing the supplements nad diet in Dr. D’s book, and asking your vets lots of questions about what they saw and how they came to that assessment, just so you understand what you are fighting for.

  2. Wanda Elliott on February 3, 2022 at 6:12 am

    My Sunshine was diagnosed with sarcoma of muscle wall. She still eats good, no bowel issues. She is on rymadal n pain killer. The last couple of days her back right leg gives out this is on the side of the mass. I’m able to get leg back in place. She is very sensitive on the right side. How do I know if it is the time to let her go? I just don’t want her to suffer .

    • Molly Jacobson on February 3, 2022 at 9:35 am

      Hi Wanda,
      I’m sorry to hear about your girl. You should give your vet a call to find out if there is anything you can do to help her, and in the meantime, you might try slinging a towel under her belly to help her stand and walk. The timing of letting her go is hard to say, and really only you will know for SURE it’s the right time. This article will help you to see how close you are:

  3. peggy on October 30, 2021 at 6:02 pm

    my dog collapsed 15 wks ago needed a pericardial centesis was diagnosed with cardial hemangiosarcoma. Hes a Golden Retreivver just turned 7. They said we could leave him there for about $2000 of tests, then taken to a vet school in our state to cardiologist. But even if they could do surgery there is no cure & he would only get about 3 months. Hes my emotional support dog never been away from me for more then 4 hours & extremely afraid of new people & places. I know he wouldn’t have lived & wouldnt put him through all that if there is no cure. They said he would die by morning if we took him home.So he was normal then it happened again about 1 month & took him to another emergency clinic. My husband said we were having the fluid around heart drained again in case its not cancer. They suggested we euthinize him . Said he had 10 percent chance of it not being cancer. and would live few weeks & would be sick. He has been perfectly normal now again since second time & been 11 weeks since second time & 15 weeks since first. So did they diagnosed him wrong ?? Hes never been sick ?

  4. Denise Hankinson on October 2, 2021 at 11:33 am

    My dog ged has bladder cancer 19 months down the line I am feeding apicsps a good diet which I follow yours he has apicsps but just notice he his losing muscle mass and a little weight he his still active. What could help him with his weight and muscles. Any advice please.
    Denise Hankinson

  5. Melissa Poole on August 6, 2021 at 2:32 pm

    Are golden has cancer on a lump on back but acts fine

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