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

Can a Dog Cancer Diagnosis Be Wrong?

Updated: May 15th, 2024

The news that a loved dog has cancer turns the world upside-down.

Shock, dismay, disorientation, anger, and profound feelings of loss or sadness are common.  Another common response is questioning the diagnosis.

“My dog seems fine.  The lump does not seem to bother her.  His appetite is good.  She still plays.  How can he have cancer?”

This question can point in two directions.  One direction is the four legged family member actually does not have cancer, and a misdiagnosis has been made.  The second direction is the diagnosis is correct, but does not appear to be.

First, let’s examine when an incorrect diagnosis has been made.  The most common way this happens is when no sample has been collected containing cancer cells, but cancer has been declared.  Samples include tissue, fluids, or cells.  These are normally reviewed to see if there are cancer cells in the sample.

Sometimes a veterinarian will proclaim cancer but has not collected a specimen for analysis.  This can happen when there is a high suspicion of cancer, for example, an enlarged spleen in a dog who is not acting right.  The problem here is that many things can enlarge the spleen above and beyond cancer.  One example is a hematoma, which can look a lot like cancer on an X-ray or ultrasound, but it not.

Sometimes a skin lump can look a lot like a cancer.  However, there are many kinds of skin lumps.  One example of a growth that can mimic skin cancer is called a granuloma, which is the body’s reaction to long-standing infection, inflammation, or some foreign material within the skin.

Of course, it is obvious what is needed under these circumstances. Collect the specimen for analysis!  See if there are cancer cells, and if so, what kind of cancer.

Why might this not occur?  Usually the veterinarian will not recommend further testing due to fear of bringing up a cost discussion, or other concerns raised by the guardian.  Rarely, the test itself will be too invasive to justify the procedure (biopsies of brain tumors, for example).

Get a copy of the Dog Cancer Survival Guide to learn more on Dog Cancer diagnosis, and prognosis

Sometimes, other parts of the process are to blame.  Here, we have proper methods being performed:  the specimen is collected to find out if there are cancer cells.  The dog’s human received the news.  However, a mistake has been made. (It should be noted that these following errors are extremely rare.)

A sample gets switched.  A name gets mistakenly put on the wrong form.  These types of errors are extremely rare, but can happen.  Under these conditions, a second specimen review will correct the issue.

This is discussed in detail in the Guide (as well as the steps every person dealing with dog cancer should take).  The Guide points out that the very first step necessary step is getting a copy of the pathology report.

In the report, the pathologist will directly state the name of the cancer.  This is important.  A pathologist report should almost always be a part of the accurate cancer diagnosis.

Occasionally, the pathologist will be stuck and cannot decide what class of cancer we are dealing with.  When this happens, a second pathologist review of the same specimen can usually clear it up, or re-sampling the area in question.

We have covered ways an incorrect diagnosis has been made.  What if the diagnosis is correct, but the guardian can’t seem to believe it?

Many times dogs will act “fine” even though they have cancer.  This is because the cancer load often has to be large before a dog will act sick.  Dogs also have a inborn instinct to hide disease.  This is because dogs acting sick in the wild are targets for predators, or may lose their pack position.

In these cases, our dogs will seem okay, but their bodies have cancer cells developing.  When this happens, it is time to change to the Dog Cancer Diet, and consider surgery, apoptogens, chemotherapy, immune support, pain control, radiation, side effect management, other supplements, and all the other steps in the Guide.

Finally, there are rare reports where the disease just goes away. Mother nature deals with it.  This is called complete spontaneous regression.  I have seen one case in the dog.  Here, the cancer was real, but the body clears it.  This is very, very rare, but deserves mention in this discussion.


Dr D


Leave a Comment

  1. Christina on December 23, 2022 at 4:51 pm

    Hi I have a 7 yrs old GSD never sick a day very healthy dog. I just noticed for few months that she slept alot seemed tired. 6 weeks ag had her well visit and shots she looked good labs all good per vet and she weighed 72 lbs.
    Two weeks after appt she started with trouble defecating and very runny stools. Back to the vet she was dewormed no worms found on stool check and she was given Flagyll. Than she started losing weight rapidly and being very picky with her food. Than she kept losing quickly down to 64Lbs We had an ultrasound and xrays of her abdomen. She had fluid in her chest area and abdomen no mass found but all tests suspicious including an enlarged spleen and lower hematocrit so mildly anemic. We even sent fluid cells for cytology some abnormal cells seen but no definite diagnosis. Meanwhile my dog is failing she is likely down few more lbs. Goes few days no food than eats just a little we can see she is slowly dying. It kills me we have no real diagnosis. I don’t think she is strong enough to handle any exploratory surgery…Vet also consulted with ultrasoujnd vet and vet told us she has never seen it so hard to diagnose and a dog failing this fast she suspects its an aggressive cancer. We are just trying to keep her comfortable any advice appreciated. I can’t understand why its so unclear.

  2. Jennifer on March 17, 2021 at 5:02 pm

    We went to the vet today as our dog started limping. We totally thought he spranged his leg and it turns out the doctor believes he has bone cancer they took x-rays and he found a sunburst he called it. I’m just not sure. It’s so sad. I have two kids 16 and 19 and this dog as been their life.
    He is Pitbull Lab mix name is noodle. Just trying to find some comfort that’s it’s actually cancer because I don’t want to believe it is.

  3. Gary Gordon on December 30, 2020 at 4:08 pm

    Hello DR, my name is Jaime ,we live in Arizona with our precocious dog nizmo. He stated with a slight limp 4 months ago, after x-rays the vet thought he had some frozen vertebrate in his neck so we started laser therapy and saw a animal chiropractor and had great results, almost back to normal, and then one awful day nizzy ran after a rabbit and we herd a yelp and he came back limping. Back to the chiropractor which said he was not out of alignment so suggested some x-rays. We went to vet Niro and they said it looks like osteosarcoma but because he had valley fever in the same leg could be fungal. Back to the vet for a biopsy, four punch biopsy which came back inconclusive, now what. We went to see a oncologist who specializes in radiation and we are waiting to get some more detailed image’s done to begin the prosses. I don’t want to have to amputate so we are trying everything. We are seeing a holistic Dr, doing conventional drugs and Chinese holistic as well as acupuncture. My heart is completely broken seeing my precious boy like this. He is 9 years young and the best dog and companion in the world, and to say he sticks to me like glue. I have changed his diet which i have always cooked for him but now i make salmon patties with veggies turmeric coconut oil, he also get organic chicken boiled with veggies as well and i put cod-liver oil on top. His meds are for pain but i have him on cbd and holistic ones as well. Please let me know what your opinion is as we are so lost especially with a inconclusive biopsy. Thank you so much for your time and many blessings for all you doing in this fight against the terrible C word.

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