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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: December 7th, 2018

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


Discover the Full Spectrum Approach to Dog Cancer

Leave a Comment

  1. Kathy Guice on July 27, 2020 at 2:53 pm

    Dr. D.? MY DOG WAS RECENTLY DIAGNOSED WITH METASTICIZED LUNG CANCER. Have you ever seen the X-ray being diagnosed as METASTICIZED lung cancer when it is actually pneumonia throughout the lungs? Of course the X-ray looks very blotchy, white blotches. My vet said it is clear that it is lung cancer.

  2. Estelle on January 8, 2020 at 6:09 am

    Good day. Our 11 year old jack russels has been diagnosed with limphonia cancer , when the Doctor found a lump on her belly. She had a high fever and lost a lot of weight . No cancer test was done to confirm this. The doctor said that her spleen is enlarged and shoe black spots on the sonar so she will only live one more month. She plays and eats as normal. We give her cortisone drugs . Can this be a misdiagnoses ?

    • Dog Cancer Vet Team on January 8, 2020 at 9:15 am

      Hello Estelle,

      Thanks for writing! As we’re not veterinarians, we can’t offer medical advice. If your vet has done a biopsy or a fine needle aspirate, they will be able to determine if the lump is cancerous. So, it might be a good idea to consult with your veterinarian and have them perform a biopsy/fine needle aspirate to confirm the original diagnosis or get a second opinion from another veterinarian 🙂

  3. Michelle Morrison on June 4, 2019 at 5:55 pm

    Hello my 9 yr old dog was diagnosed with lymphoma after a biopsy was done. That was in January. She looked terrible & sluggish. It is now June and lumps have almost gone. Her energy is coming back. She had no treatment! How is this possible. Several times I thought I should have her put down but I just couldn’t do it. Does this make her a miracle or is it the calm before the storm?

    • Dog Cancer Vet Team on June 5, 2019 at 8:26 am

      Hey Michelle,

      Thanks for writing! It sounds like it might be a good time to get a second opinion (if you are concerned that your girl was misdiagnosed), or to get a second fine needle aspirate/ biopsy done, to see what is going on. As we’re not vet’s we can’t tell you what might be happening, but it is always a good idea to check in with your vet if you’re noticing any changes 🙂

  4. Mary on December 31, 2018 at 3:48 pm

    Hello Dr Dressler. After a chest x-ray showed a white mass in my dog’s right lung the vet said it was most likely to be a tumour. He had had a cough and the vet removed eight teeth and cleaned tartar off his teeth and said he had some gum disease which should clear up. Could it be something else other than a tumour?

    • Dog Cancer Vet Team on January 2, 2019 at 2:12 pm

      Hello Mary, thanks for writing, and we’re sorry to hear about your pup. We’re not veterinarians, so we can’t say for sure what else it could be, but for sure any mass that shows up on X-rays in the lung will most likely be a tumor. Pneumonia or other lung irritations look different on X-rays. However, the best person to ask this question is your veterinarian. It’s an entirely reasonable thing to ask! He or she will be able to tell you what else it could be, if anything. We hope you hear good news.

  5. Lauren on September 25, 2018 at 1:38 am

    I have 3 dogs that are now almost 11 years old and I am terriefied of Vets for this reason. I took my then 5 year old golden retriever to a highly recommended vet after finding a lump. They said the tumor appeared to be cancerous and made me wait while they biopsied it and took a sample. They told me they would call me in a few days but to start thinking about whether I would put him down or make him go through treatment which would greatly affect his quality of life. Needless to say I was wreck and started treating him like it was his last days on earth. A few days later the lump was almost gone which I thought was odd. The vet finally called me and confirmed the biopsy had confirmed it was cancer and I’d need to bring him in to discuss our options and they wanted another biopsy. I was told he had about 6 months to live. I asked her what if the lump is gone? And she sounded shocked and said “well then keep an eye on it and if it’s gone he will probably be fine” he’s now 11 years old. This was so long ago I don’t remember the cancer they thought it was but it completely ruined my faith in vets. It was a very expensive learning experience and I’m glad whatever the real issue was resolved itself before I put him through unneeded treatment or even worse if I decided to put him down. My point is you never know and with something as serious as cancer I always say get a second opinion.

  6. janet steenburg on August 13, 2018 at 11:14 am

    Dear Doctor Dressler
    I have a 130 pound 4 year old rott that has recently been diagnosed with lympnoma. My vet started him on predisone and the swelling went down about a month into it they started swelling up again so we started the kemo which seemed to be working for about the first three treatments then again it stopped working and the swelling started back up. he acts fine athough we all no he is sick and his time is limited, the vet wanted to try another brand of kemo that we originally were going to try but it is claimed that it can cause heart failure in the rottie breed so we went with a different kind. since this kind did not work we decided to try the other one only to find out it is no longer being made and we can not get it. I am at a complete loss and I could really use any sugestions or ideas you may have. please help thank you

  7. Michelle Marsh on June 5, 2012 at 9:33 am

    Our 2yr old puppy has cancer. At first they thought she had valley fever, but when the medication didn’t work they did another x-ray and a soft tissue biopsy and sent it to a pathologist they said it was cancer. We then took her to an oncologist for both a second opinion and to find out what our options were. I am very sickened by the amount of money vets charge to treat our pets and the fact that the first thing they want to do is chop the limbs off. Breakdown (our puppy) has it in her right hind knee. She appears fine otherwise. We cannot afford the 1000 plus dollars for an amputation with no guarantee it will extend her quantity of life! Not to mention it would be about 400 or so dollars to do a bone biopsy to find out what kind of cancer it is for sure. They suspect Osteo but we don’t have the money to find out for sure, nor do we want to put her thru more pain to find out. So far we have tried marine plankton, and NuVet supplements along with medication for her pain. She has Novox along with Tramadol and something else I can’t think of right now for the pain twice a day. Not sure what to try next. Her leg swelling appears to be getting larger and it is hard and warm to the touch. The thing is that I am a widow with 2 kids and major debt and I don’t have money to spend here there and everywhere but I want to save our puppy. Any suggestions would be helpful. It has been 2 months since her diagnosis.

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  9. Bitta Waddell on December 11, 2011 at 12:40 pm

    Dear Dr. Dressler,

    first of all I would like to say thank you for all the help you provided (thru internet anly, but still very good). When my Border Collie was diagnosed with Analgland Carcinoma in April this year I contacted you and I followed all your recommendations: cancer diet, Apocaps, MCP, Artemesinin, fish oil, etc. He is doing so well, the tumor hasn’t grown at all since then. My local vet cannot believe it and we both have learned a lot. Therefore, thank you sooo much. My dog also has a slight problem with incontince (bladder) and my vet gave me Ephedrine. Can I give it to my dog without influencing the cancer treatment? I really dont want to interrupt, what obviuosly is working.

    Thanks again,
    Britta Waddell
    New Zealand

    • Dr. Demian Dressler on December 21, 2011 at 7:46 am

      Dear Britta,
      great to hear the good news! Keep up the good work. Discuss with your vet, but I see no immediate problem between the ephedrine and the cancer therapeutics…we use phenylpropanolamine over here in the US. Be sure the have the urine tested so we know there are no other issues going on…(infection, stone, crystals, etc)

  10. Iris Menachem on December 5, 2011 at 2:51 am

    Just uploaded the Guide on Kindle. I lost my heart dog to OSA 2 years ago. Although both my present dogs are well, once you have a dog with cancer (I’ve had 3), I want to be prepared just in case. Thank you for sharing all this information. Hopefully, it will help keep my pals healthy.

    Iris Menachem
    Quanah, 9 yr. old GSD & Murphy, 3 yr. old pit bull mix

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