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Multiple mast cell tumors.

Species: Dog
Breed: boxer
Age: 5-8 years
Hi Marie, it says that my question has been answered, but I do not know how to retrieve it. In the meantime, I found my dog's initial surgery on youtube, go figure. Please take a look?

Online vet, Dr. Marie

Dr. Marie replied:

Hi Teresa....I'm not sure why you got a notification that your question has been answered as I haven't done it yet! But I will now. I'll refund your initial payment for a 24 hour response as well.

Here is your original question:

I have a 6 year old boxer that lives in Bocas Del Toro, Panama. In September 2011, the local vet removed what he diagnosed as a mast cell tumor on the Boxer's right side. It was about the size of a dime ad was flat. By April 2012, 5 more superficial tumors appeared in the same place and another lower on the right body near the top of his right shoulder. They were elongated and oval to me appeared similar to those lesions caused by bot flies. Bot flies ruled out and he was tested for leishmeniasis he tested negative so the 6 tumors were also removed. During this April 2012 surgery, there was a small tumor that was missed above the other 5 as it was the size of a pea. Within 2 weeks it grew to the size of a marble. Another was apparent on his left shoulder and yet another on his right neck below the ear. We sent him back to yet remove another 3 tumors. He has been home for less than two weeks and I can now count another 7 the size of peas, but they are increasing in size, including one on his penis. Please can you explain why there has been an increase in the number and growth of the tumors. Are these possibly not mast cell? What else may they be, and what can I do to stop them. The surgery seems to be making the situation worse. Any insight would be greatly appreciated

What a frustrating situation for you! Boxers definitely can be prone to getting mast cell tumors. I have not personally seen one get as many as Paunch has had though. I did do some research for you and found that there are some boxers that can get multiple tumors.

Do we know for certain that the new tumors are mast cell tumors? It should be relatively easy for your vet to determine that by doing a fine needle aspirate. It should be something they could do right in the clinic and not have to send it to a specialist as mast cell tumors are usually quite easy to diagnose.

If a dog does have multiple mast cell tumors, then the recommended treatment is indeed to keep removing them. But I can understand how frustrating that must be though!

I just did some research for you to see what other vets have done in cases like this. What I learned was that the good news is that most of the time, in boxers, mast cell tumors tend to be low grade which means that they are unlikely to cause disease. One acceptable treatment, when a boxer dog gets multiple mast cell tumors is to simply leave them. If we do this, though, there is a small chance that one or more could end up being more aggressive and spread to cause cancer in other places in the body.

I also did some research for you on whether medications could help to prevent these. I wondered if perhaps putting Paunch on antihistamines (as mast cell tumors produce histamine) or steroids would help at all. The experts say that it will not help.

Unfortunately, again, the recommendation is to remove new tumors as they come.

So, to summarize:
-If you're not certain if these new tumors are mast cell tumors then your vet can aspirate them to find out.
-If they are mast cell tumors, the best treatment is to remove new ones as they come up.
-If this is too costly for you, then it is an option to simply leave the tumors. The odds are in his favor that they will not make him sick or spread. But there still is a small risk that that could happen.

I hope that helps. I am only online for a few more minutes tonight, so if you have more concerns let me know. If I miss you tonight, I will check in on your question in the morning.

Dr. Marie.

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Customer reply:


Again, I am in Panama, so I can only take what the Vet says that he has confirmed they are indeed mast cell.
The cost of course, if concern; however, the fact that I may be making them worse is greater

Please confirm that you can see the photos

I hope to show 1) how strange the tumors look
2) how the cuts are left (Paunch is not in pain, but I feel so bad for him)

Online vet, Dr. Marie

Dr. Marie replied:

Ah, sorry...I don't have the ability to upload photos yet. You can email me the photos at

I am heading to bed now, but I will have a look at your photos in the morning and let you know what I think.

Dr. Marie.

Online vet, Dr. Marie

Dr. Marie replied:

Thanks for the photos. I've included two of them here in my answer. Here is one showing the tumors:

tumors on a boxer

And here is the post surgical one:

boxer after tumors removed

I can't say that I have seen tumors that look exactly like this, in clusters. I can say though that mast cell tumors can have different kinds of appearances. Again, it's not difficult to determine if these are mast cell tumors. If your vet feels confident that this is what these are, then I would believe them.

I'm a little puzzled about the post surgical photo. It looks like the skin was not sutured together but rather was left to granulate. This would only be done if the area was too large to suture. Usually, in this area (i.e. on the side of the dog) there should be sufficient skin to be able to close a wound like this. But if it was a very large area, I could see that this is possible.

It's tough to advise you on how to proceed. If these are mast cell tumors then they can keep on appearing and there is not much we can do to prevent them. I can understand your reluctance in having continuous surgeries to remove them. But the only other option is to leave them, and judging by the picture, they are not pleasant (and possibly uncomfortable for the dog.)

I wish I could give you more helpful advise!

Dr. Marie.

Customer reply:

Hi Dr. Marie,
Please charge me $15 more for further investigation. I know you can't do magic, but I am in desperate need a solution, as I feel helpless.
I stumbled upon a photo today of a sebaceous cyst (photo link sent to your email) . It is a brindle boxer.
As I had mentioned, I am a foreigner in panama on a remote island. our veterinarian care is limited to 3 island vets and 1 clinic where they can actually recuperate our pets. So I have really only one "local" opinion to rely on. I have paid $600+ for the 3 surgeries.
What if the vet had misdiagnosed the lumps (purposely or not) Based on this photo and the rapid growth of the lumps is there a chance my dog could have sebaceous cysts and not mast cell tumors? How might I further research the condition. Once again,
Truly thankful, Teresa

Online vet, Dr. Marie

Dr. Marie replied:

No need to pay more, Teresa. I see LOTS of sebaceous cysts and they are very very different than mast cells. When you put a needle in a sebaceous cyst they are full of material that looks like cottage cheese.

I really do think, from what you have described, that these are mast cell tumors. Again, it's quite easy to diagnose them with a fine needle aspirate and a microscope. Also, I have read several reports of boxers that will get multiple ones that pop up just like Paunch's.

Customer reply:

Hi Dr. Marie,
You truly are kind. I feel that you truly care
I went to see another vet (Spanish speaking only) he wants to use oncovin? Do you have any expertise with this drug? He claims it will slow the rapid production of the tumors.
Thank you, Teresa

Online vet, Dr. Marie

Dr. Marie replied:

I don't have much experience with Oncovin (also known as vincristine). It's a chemotherapy drug.

I did do some research for you about using oncovin for dogs with multiple mast cell tumors and it looks like most oncologists in North America don't feel that it is helpful to prevent new mast cell tumors. It is something that we can use when dogs have a type of mast cell cancer that is spreading internally to organs. But in Paunch's case, these are brand new tumors that pop up and not a spread.

In doing my research I found a fascinating discussion amongst veterinary oncologists (cancer vets). They were talking about dogs who get repeated mast cell tumors and how frustrating these cases were. Some of them said that they have tried chemotherapy - usually because the owners were frustrated with continuing to have to do surgery. But unfortunately all of them who tried chemotherapy were disappointed with the results. There was one vet who mentioned a study that claimed that dogs on an NSAID (a drug such as Metacam, Rimadyl, Previcox or Deramaxx) had a much lower rate of the mast cell tumors coming back.

These vets were also commenting on how they felt that dogs who kept producing mast cell tumors had a genetic predisposition to do so. It seems like it is a genetic defect that causes some dogs to do this. They all commented on how frustrating this condition is.

With all of this being said, I don't want to contradict your vet. If he has experience with this drug and has evidence that it has worked in other cases, then I would say to give it a try.

Customer reply:

Dr. Marie! now you are talking my language. I am HLAB27 positive (ankylosing spondylitis) NSAIDS (celebrex), diet, and Enbrel turned my health around. What is the recommended dosage of NSAID for dogs? daily? weekly?
One final question: Are you familiar with any studies or success with T-cell inhibitors and canine mast cell? Enbrel or Humira?
Thank you, thank you, thank you
I will follow up with you and let you know what I do, and what the success is
Sincerely, Teresa

Online vet, Dr. Marie

Dr. Marie replied:

The dosage would depend on the type of NSAID prescribed. That would be something your vet would need to decide on. The NSAID would likely be a dog specific one, not one that you can buy over the counter.

I am not personally aware of any studies on T-cell inhibitors and mast cells...sorry!

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Dr. MarieDr. Marie is a veterinarian who practices in a busy animal hospital in Ottawa, Ontario. She created Ask A Vet Question as a resource for good, accurate veterinary advice online. Dr. Marie treats dogs, cats, hamsters, guinea pigs, and rats. She has been a vet since 1999.

Is an online vet visit just as good as a trip to your veterinarian? No! But, many times, asking an online veterinarian a question can help save you money. While Dr. Marie can't officially diagnose your pet or prescribe medications, she can often advise you on whether a vet visit is necessary. You can also ask Dr. Marie for a second opinion on your pet's condition.