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

Mast Cell Tumor Internal Spread

Updated: May 15th, 2024

It is important to tell whether or not a dog tumor has spread internally.

This question is not only very frightening for a dog lover, but also has some real medical ramifications.  So let’s take some time with this concept and mast cell tumors.

Mast cell tumors are very common in dogs.  They come in three grades (1, 2, or 3). Although they are all considered “potentially malignant”, the odds are that most grade 1 mast cell tumors are benign.

However, many grade 2 and all grade 3 are malignant and can be life-threatening.

Different cancers have their favorite spots to spread. Some spread to nearby locations, in the surrounding area next door to the tumor.  This is called local invasion. Some other cancers spread in the circulation, which is called metastasis. Some do a little of both.

These cancer cells have certain areas where they like to go.  The preferences seem to be created by cross-talk between the outside of the cancer “seed” cell and the area the cell settles in (the “soil”).  For more, click here and here.

Now, if we take mast cell tumors as an example, first we need to get our data.  We need to have found out that we are dealing with a mast cell tumor, and whether this tumor is a high grade 2 or a 3.  These have high metastatic rates.  For this reason, a biopsy should be done on mast cell tissue surgically removed to get the grade.

Once we know we have a mast cell tumor and the grade, we need to start the steps outlined in the Dog Cancer Survival Guide.  First, maintain composure so you can best cope most effectively with this news. Next, get your data and contemplate the different treatments available discussed in the Guide.

These include diet, chemo, surgery, radiation, immune support, life quality enhancement, supplements like Apocaps and others, pain control, antihistamines, antimetastatic treatments, and so forth. This analysis is done with help from your conventional vet, oncologist, and/or integrative vet primarily.

Now, the question that quickly arises is whether the tumor has spread or not.  It turns out that mast cell tumors have what is called a “tropism” or a preferential movement or attraction, towards certain organs.  These include first the spleen, then the liver, and also the lymph nodes and bone marrow.

Some areas of the body are visualized pretty well with X-rays. These include mainly bones, some other orthopedic structures,  and the lungs.

However, the soft tissues like the spleen and liver are best seen with an ultrasound. This is the tool that is used in pregnant women to evaluate developing babies.

So please make sure that when your dog has a mast cell tumor that has the potential for internal spread, ask for an ultrasound!


Dr D

Leave a Comment

  1. rose on February 15, 2011 at 3:21 pm

    our dog drake just got his report back form the vet. he has a a mast cell tumor the vet said it is “more likely” a stage 2 or 3 but does not specify one or the other. the vet has also said the mast cell tumor has spread. we are taking him to a specialist in 2 days, but my question is how do they know the mast cell has spread. the biopsy was only taken on his chest area where he has 1 lump, form what ive been reading you need an ultra sound to know if it has spread to the spleen and other internal organs. so im wondering where this mast cell could have spread to?
    your help is much appreciated as are your blogs.

  2. Robert McKenna on February 1, 2011 at 1:04 pm

    My 14 year old Jack Russell had surgery one year ago to remove a tumor on her liver. It was first diagnosed as benign, but when the cytology exam came back it was determined that there were some cancer. Her liver enzymes have been normal since then, until her most recent exam, when they are elevated. I’m wondering if Apocaps are OK for a dog with liver history. If not what kind of other diet or supplement could help fight this?

    • DemianDressler on March 8, 2011 at 9:45 pm

      Dear Robert,
      I use Apocaps at 1/4 the labeled dose in cases like this. Make sure your vet is involved and the liver markers are monitored. Have you read the Guide? Beta glucans (K-9 Immunity and transfer factor) and omega-3’s might help too.
      Dr D

  3. Brenda on December 27, 2010 at 9:36 am

    My yellow lab was diagnosed with mast cell cancer, stage 2 when he was 2 years old; he is now 4 1/2 yrs. old and shows no signs of illness. He did not receive chemo or radiation as it was not recommended at his young age, leaving a poor prognosis of recurring tumers. What should I be looking for to know if the cancer is spreading without the expense of ultra sounds & X-rays?

  4. Marian Beeman on October 25, 2010 at 3:38 am

    Dr Dressler, My 11 year old Beagle Mix was just diagnosed with a Mass cell tumor, grade II with a mitotic index of 2. I read one of your blogs that for me was a little confusing as you mentioned that if the tumor has a mitotic index of less than 5, it usually will behave less aggressively and in your opinion do not require surgery, as long as you have clean margins on the removed tumor.

    Does this mean I should not go ahead with the surgery or should I go ahead with the surgery from the biopsy results mentioned above. The tumor is on the right Thorax and is quite large measuring 4x3x3 cm and because of her age and the size of the tumor, I am hesitant to have it removed, if it is less likely to move to other areas of her body. Please advise as soon as possible, as I have an appointment with my surgeon on Wednesday 27 Oct 10 and would like to make a decision as soon as possible. I would also like to ask if I should start treating her with any chemo drugs, as my oncologist suggested I start treating her with Palladia. She has shown no signs of discomfort other than when they took the biopsy, she did vomit the next day and has been suffering from Allergies all summer, which I have now started her on Tagament, which has helped considerably and Benadryl.

    Thank you,

  5. TRACEY ANN ARMES on October 22, 2010 at 9:09 am


    My 7 1/2 yr old male shar-pei is being treated with masivet for mast cell tumours on his right hock for the last 4 weeks turmours have broken down, bloods are all clear and major organs no problems. I am still very concerned if these cells with find a new home within his body after reading blogg would the next home be his spleen or liver?

  6. David on October 18, 2010 at 12:05 pm

    Dr. Dressler,

    I have a beautiful 8 year old Australian Shepherd with 3 Mast Cell tumors. We’ve known about the larger tumor for about 2 years but our old vet said it was nothing to worry about and never did a needle biopsy. We went to a new vet and she discovered 2 other small tumors that were also Mast Cell. On tumor is on the right front shoulder and the two smaller ones are on the left side. The larger tumor is in an area where it will be hard to cut deep enough to get to get the recommended margin without causing mobility problems.

    Her advice was not to have the surgery because once there was more than one tumor it was unlikely that the surgery would actually help.She’s a healthy dog and is showing no signs of the cancer. Are multiple tumors a reason not to have the surgery?

  7. Deborah Sazma on October 18, 2010 at 6:14 am

    My 11 year old cocker spaniel just had a mast cell tumor removed from her right rear paw (topside).
    The tests showed a grade 1 / 2.
    She also was diagnosed in Stage 1 kidney failure, we are treating that with a change in diet and Omega 3 capsules. She seems to be doing well.
    She is retired from agility but stills competes in Rally & Obedience.
    Is there a strong possibility that this mast cell will come back and attack another area of the body?
    And is she eligible for chemo, radiation treatment?

  8. stuart lang on October 18, 2010 at 12:38 am

    Massivet- 10 months later, seems to be working well on my 11 yr old lad. At this present time all bloods and tests are clear of mast cells.

    fingers crossed it keeps working.

    stuart lang


  9. Paulette on October 15, 2010 at 8:58 pm

    My dog has mast cell tumor on right back foot after pad. Had surgery in August and within 3 weeks another tumor grew in same area. It has grown so big. My dog has taken off her bandage and bit the tumor which has many nodules.
    What can I put on the tumor? Do you think blood root would kill off the tumor?

    Is there an alternative for the ecollar? How can I stop her from bitting her bandage?

  10. Andrea on October 15, 2010 at 11:54 am

    Hi Dr.

    My 6 year old yellow lab has mast cell stage III with a high index. All sounds bad. She had the tumor removed and it was in the middle of her chest- oncologist said if any area is a good one this was for her. She had ultra sound and nothing has spread to liver, spleen, lungs, lymph nodes etc. at this time. She is getting chemo. (4 treatments- 2 completed). Her blood work was all ok so far and oncologist feels no growths in that area of her surgery. She was immediately on benedryl and pepcid after surgery. Also on prednisone at this time. 20mg.
    She has no side effects at this time from the chemo.
    Trying to be hopeful but reading everything is not giving much hope.
    Do any dogs survive longer than a year with this this diagnosis?

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