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Help for Dogs with a Mast Cell Tumor

I found a lump on my dog. These are words no dog parent ever wants to say, but lumps on a dog are very common and may increase in frequency as a dog ages. If you are reading this post, your dog has likely been diagnosed with a mast cell tumor. Often dubbed the “Great Imposter,” any lump on a dog needs to be examined by a veterinarian.

When a tiny raised lump appeared on my Cocker Spaniel’s shoulder blade about two weeks after getting her then yearly vaccinations, I felt a twinge of “something isn’t right” course through my veins. But I waited – after all a raised, small but swollen area at the site of vaccination is common, according to the veterinary literature I read. (at the time that didn’t mean Internet, it meant the UC Davis Book of Dogs). My dog’s veterinarian at the time tried to “squeeze” the lump and said it was probably nothing more than a pimple. Whew.

“Come home quick, Brandy’s lump is bleeding,” my wife called me at work to flip my day upside down.

“Your dog has cancer and we need to send the pathology out for confirmation of the stage,” said the man in the white lab coat.

The C Word. You could have knocked me over with a feather.

An emergency veterinarian (and second opinion) were summoned to examine Brandy’s “bleeding lump.” After laser excising it, initial reports showed cancer, with an outside laboratory confirming stage II mast cell cancer.

My forever loved baby, Brandy Noel

I learned more about mast cell tumors and lumps on dogs along with the over vaccination epidemic in this country in the months that followed than I ever imagined. The great imposter is what Kate Connick called mast cell tumors in her cancer crash course website. “Mast cell tumors vary widely in their size, shape, appearance, texture, and location,” she wrote.

An oncologist at Cornell gave me a rudimentary diagram of a dog and told me to chart Brandy’s lumps. After a few years, I could have connected the dots, so I pass this advice for dog lumps and bumps screening onto you:

  • Photograph each new lump and keep the image safe and secure. Be sure to note EXACTLY where it is located on the dog’s body. When you write “ear,” that might not make a lot of sense if more lumps develop.
  • Invest in calipers. I got mine at a hardware supply store. Calipers minutely measure the width of a lump. Document it. Monitor the lump for any sign of growth or physical change. See the veterinarian.
  • If a lump occurs, see your vet. When Brandy had a few lipomas (warty growths), I had them all removed when she was under anesthesia for something else. Cockers tend to have more sebaceous oil in their skin than other breeds, so lumps are somewhat expectant.
  • DON’T squeeze it. No no and no. This can lead to infection and is a generally bad idea.
  • DON’T panic.  Out of over 25 aspirations in her lifetime, ONE turned out to be cancer. One too many.
  • Know the warning signs of canine cancer.

cocker spaniel

Dedicated dog mom Nancy B., regularly runs her fingers through her Cocker Spaniel’s coat. She touches his skin and ensures to examine his body, armpits, belly, and gives him a thorough scan with fingers and eyes. Of course, her dog, Mayor, thinks he is getting a puppy massage. Thank goodness for Nancy’s due diligence: Twice she found small lumps on her dog and twice they have been removed. Both times, mast cell cancer was the diagnosis. Mayor has been given a stage II, so now they must seek the help of a veterinary oncologist. He has had two lumps appear on the skin within months of each other.

Help for mast cell tumors in dogs

Mast Cells and What They Are

Mast cells like in the connective tissues of the body. Humans have mast cells, too. The function of a mast cell is to defend the body against parasites, to repair tissue, and to help form new blood vessels. When an allergic reaction occurs, the mast cells come into play because they contain granules comprised of heparin and histamine. Think of when a foreign invader comes at the body: Histamines flare up and the mast cells serve to modify the immune reaction. You’ve heard of antihistamines, and they serve to block the receptors of histamine. Those of us with allergies can relate to the efficacy of anti-histamines, especially during flare ups.

Mast cells are derived from the bone marrow, and can be found in various tissues throughout the body.

The folks at petMD describe mast cells this way:

Mast cell tumors (or mastocytomas) are graded according to their location in the skin, presence of inflammation, and how well they are differentiated. Grade 1 cells are well differentiated with a low potential for metastasis; Grade 2 cells are intermediately differentiated with a potential for locally invasive metastasis; and Grade 3 cells are poorly differentiated or undifferentiated with a high potential for metastasis. Differentiation is a determination of how much a particular tumor cell looks like a normal cell; the more differentiated, the more like the normal cell. In general, the more differentiated the mast cell tumor is, the better the prognosis is.

lump on dog
A lump on my dog, Dexter, that is benign and we monitor.

From a Veterinary Perspective

Dr Patrick MahaneyI asked Dr. Patrick Mahaney, a University of Pennsylvania-trained veterinarian and Certified Veterinary Acupuncturist (CVA), to tell us if he knows of any pet parents who use antihistamines as preventative option for Mast Cell Tumors (MCT).

“I’ve had patients take antihistamines once they’ve been diagnosed, but not before as a potential MCT preventative,” Mahaney says. He goes on to say that antihistamines and steroids can be used to control inflammation associated with MCTs and potentially keep them from degranulating.

When an MCT degranulates (loses granules as part of an immune reaction), a variety of chemicals having effect to dilate blood vessels, reduce blood pressure, the movement of white blood cells, and have other effects are released into tissues adjacent to the MCT and into the blood stream.  Effects of MCT degranulation can be mild to life-threatening.

Additionally, taking nutraceuticals (supplements) containing natural anti-inflammatory substances, like Omega Fatty Acids (Omega 3 and 9), turmeric, ginger, phycocyanin (blue-green algae extract), and others can help to reduce the overall level of inflammation.

Putting a pet on antihistamines during allergy season is typically fine provided the dog isn’t having any side effects and if the use of antihistamines helps in some capacity.

A Veterinary Oncologist Speaks Out

Avenelle Turner, DVM, DACVIM (Oncology), has thoughts on this topic with mast cells and the use of antihistamines.

Dr. Turner says that most oncologists recommend chronic antihistamine therapy for any pet diagnosed with a high grade or multiple low grade cell tumors since the signal for mast cell tumors is histamine.  Also there is no long-term side effect by using antihistamines long term.

“There are no clinical studies that I am aware of that would document the specific medical benefit using an antihistamine in this setting,” she says. “But since there is no medical disadvantage of using an antihistamine long term and there is a theoretical advantage to using an antihistamine long term, utilizing an anithistamine may have a benefit.”

dog at veterinarian

What I Did For My Dog With Mast Cell Tumor

  • Laser surgery showed clean margins so a second procedure was not needed.
  • Abdominal ultrasound every 6 months for two years from a university that does them regularly. The vet and oncologist wanted to be sure the mast cells did not spread to the liver or spleen, and an abdominal ultrasound would show this.
  • Monitor closely and aspirate for any new lumps that form.

After 2 years’ time, I am happy to report my dog was cancer-free and never developed another tumor until near the end of her life, and that tumor was not the cause of her death.

Treatment depends on the classification and grade of your dog’s mast cell tumor. From the National Canine Cancer Foundation:

Classification of Mast Cell Tumors

Mast cell tumors have been classified according to their degree of proliferativeness. The higher the grade, the more aggressive the tumor.

  • Grade I: Occur in the skin and are considered non-malignant. Although they may be large and difficult to remove, they do not spread to other areas of the body. Most mast cell tumors belong to Grade I.
  • Grade II: Found below the skin into the subcutaneous tissues. Their cells show some characteristics of malignancy and their response to treatment can be unpredictable.
  • Grade III: Originate in areas deep below the skin, are very aggressive, and require extensive treatment.

Staging Mast Cell Tumors

Mast cell tumors should be staged because it gives us an idea about how they have metatasized in the body. A tumor is staged after it is surgically excised and examined, along with the surrounding lymph nodes. The factors on which staging depends include the number of tumors present and lymph node involvement.

  • Stage 0: One tumor in the skin incompletely removed, with no lymph node involvement.
  • Stage I: One tumor in the skin, with no lymph node involvement.
  • Stage II: One tumor in the skin with lymph node involvement
  • Stage III: Multiple large, deep skin tumors, with or without lymph node involvement
  • Stage IV: One or more tumors with metastasis in the skin with lymph node involvement. This stage is further divided into those that have no other signs (substage a) and those that have some other clinical symptoms (substage b).

We raise our sparkling water dish in a wish that your dog lives a life free of lumps and bumps. Don’t take chances should one (or more) appear: Seek veterinary care.

learn more

If you liked this article and want to learn more, please read here:

What to Do For Lumps on a Dog

10 Touches That May Save a Dog’s Life


  1. Jessica Harlow says

    Taking a photo of any lump or bump is a really good idea. It helps you gauge whether there are any changes (size, color, etc). Thanks for the tips on keeping our furry family members healthy!

  2. Heidi says

    Hello Carol,
    This is a wonderful article written under difficult conditions. Thank you for sharing. I might suggest a few additional herbs and supplements as potential adjunctive therapies when mast cell tumors/lipomas present. We are cheering for you and your puppy love!

  3. Tiffany Cruz says

    My mom’s dog has a lump of some sort on his head. I’ve asked my mom about it and she doesn’t seem concerned about it. I think she has had it checked before by the vet. I’ll have to share this post with my mom.

  4. M. K. Clinton says

    Those are words that I pray to never hear from my vet. I noticed that with my Golden Retriever, as he got older, many of the places where he received cortisone shots for allergies over the years developed lumps. I won’t allow Bentley or Pierre to have a cortisone shot unless the vet feels it is absolutely necessary to provide relief. This is great information, Carol. Thank you ☺

  5. Katherine says

    Our Sussex Spaniel was diagnosed with a grade 1 mast cell tumor at the age of 2. It was removed with a good margin also excised. That vet never prescibed follow-up steroid therapy. He was healthy until aged 6, when he developed another mast cell tumor and this time, after surgery with a much better vet, he was prescribed the steroids. He didn’t stay on them for more than a year. When he died, at age 12, it was not from cancer.

  6. MattieDog says

    Great article – having adopted a lot of seniors we are very cognizant of feeling our pups for lumps and bumps! We’ve lost three dogs to cancer – and it’s very similar to a humans clinical pathway once diagnosed. Your article does a great job of taking somewhat complicated and foreign terminology and situations and putting them in laymen’s terms. We support the use of complimentary therapies as well, including holistic and acupuncture!

  7. Beth | Daily Dog Tag says

    This is a lot of valuable information. So far, none of my dogs have any lumps, but now I have a better idea of what to do if I find any. I think the recommendation of documenting with photos and using calipers are excellent suggestions.

  8. Christine Caplan says

    Dr. Mahaney’s perspective is really interesting. I find some of the rules around using antihistamines confusing when it comes to MCT. I’m also glad the oncologist said there were no long term side effects.

  9. Denise Gruzensky says

    Invaluable information! I really like the idea of taking a picture and measuring with calipers! Shasta has a lump on his shoulder & 2 different vets have said it is a sebaceous cyst but for some reason I can’t stop worrying.. I’ll be taking a picture and start with more than an eye ball measurement right away to help me keep an eye on it. Thanks!!

    • Carol Bryant says

      It’s amazing, too, how the calipers can measure something and maybe it grew – but to the naked eye it looks the same.

  10. Elizabeth Keene says

    Dewi had a growth in his nostril about three years ago that gave me a scare. The vet took a photo and told me it was probably a wart, but to watch it for a week and report back if it changed. About 2 days later, it just spontaneously disappeared. It was a wart (but in an odd place for a dog). I hope that was and remains my only experience with a dog lump. Or cat lump, for that matter. *sigh*
    Hope Dexter continues without any changes in his single lump and that no more occur! Such a thorough article that could help LOTS of people who need it!

  11. Suzanne Dean says

    Thanks Carol for such detailed information. Knowing your dogs body is so important so you will notice changes. I especially like how you explained how to keep a detailed log of the who, what, why and where of any lumps. This is a great post, most worthy of sharing. Thank you again!

    • Carol Bryant says

      Thanks for saying that. I really want dog moms and dads to touch their dogs and document lumps and get them checked. It can save a life.

  12. Sweet Purrfections says

    Excellent information. My previous Persian, Sweet Praline, had a mast cell tumor that was removed from the side of her nose. The vet said it wasn’t malignant and that she’d be okay. Less than a year later, she had to be helped to the bridge because of a large tumor in her digestive system. I’m sure the two were related.

  13. Christine says

    This was great… I always check for bumps and lumps on my girls since I am constantly brushing them… I am going to get a shih tzu drawing to chart anything I find… thanks for these tips on what I can do.

  14. Sadie says

    Henry is covered with lumps and bumps. I’ll never forget that feeling, when I found the first one. Of course I suspected the worst! Thankfully his Dr. tested him and it’s just ‘one of those things.’ Great information for people struggling with a different diagnosis!

  15. Cathy Armato says

    Excellent post, thanks so much for this detailed information. You are always so thorough Carol which is much appreciated. I have a hard time checking my Husky for bumps, her coat is SO thick but I do my best

  16. Greg Tynan says

    There is significant research by a company in Australia called QBIOTICS they have had great success with treating these tumors in various animal types and are working toward US approval for their treatments which do not involve surgery

  17. Greg says

    My beautiful boxer dog had MCT grade 3 & it wasn’t operable so I put him on Massive which shrunk the tumor for almost a year then stopped working so I changed it to Palladia & steroids which shrank the tumor for another year but his quality of life eventually got worse probably more to do with the long term steroids with muscle weakness & hardened skin which started to break open & swelling of the feet and difficulty in getting up.
    So after 2 years of MCT 3 the quality of life was slipping away and I could not bear to see once a such active boxer dog suffer so we sent our lovely boy to heaven.

    I still have lots of Palladia left but can’t bring myself to throwing them in the bin if a dogs charity could make use to them in the UK

  18. Wendy Anderson says

    Thank you so much for posting all of this information. Just got back from the vet about 2 hours ago. Annabelle, our 5 1/2 year old Aussie had a strange red lump on her right back leg. Doc said she believe it may be MCT. Annabelle is scheduled for surgery next Friday. Your information has given me the tools I need to be proactive for Annabelle’s care. I’m off to the hardware now to buy calipers and we will photograph and document prior to surgery. I will also contact the University of Florida’s Vet Division to schedule her first diagnostic films six months from now – regardless of stage/grade findings on the future pathology following surgery. Will also be talking to vet about antihistamine therapy. I would like to respectfully add one thing to your information which I found during my research — it is best to clarify with your vet that the pathologist is a vet pathologist versus a human pathologist. Human pathologist have historically misdiagnosed tumors as malignant when they were actually benign. This is not meant to be a negative statement about human pathologists. Again, my husband and I sincerely thank you for taking your time to post all of this very valuable information.

  19. Cheryl Bennett says

    About 5 years ago, we had an english setter who had a lump show up when she was about 7 or 8 years old. After surgery a new lump showed up within 2 months. We had surgery again, and the pathology showed mast cell tumors. She was put on prednisone, which did help her for a few, maybe 6, months. But she continued to get several tumors, and within the year she had a huge tumor and we had to put her to sleep. It was so sad, but the tumor was huge on her chest, and she got to a point at which I could tell it would be kinder to her to let her go. Our vet said it was the most aggressive case he had seen.
    I appreciate reading your update on treatments. I wish there was more we could have done.

  20. Rob says

    Following an earlier post, I thought I’d look into QBIOTICS … some amazing progress with “tigilanol tiglate” for treatment of MCT !!

  21. Kiky says

    I just lost my sweet, 13 yr old Pittie Bella to this type tumor. She’d had many stage I, and I think one stage II mast cell tumors removed, but then we didn’t catch one in time that was staged a III and it spread to her spleen and lymph node in her belly, which is where I first noticed it. About 2 months after the diagnosis that the tumor had spread to her spleen is when I had to have her euthanized because it became painfully obvious to me that SHE was in such pain. It seemed to grow/worsen so quickly.

    My heart is broken, but unfortunately she is not the first furry baby I’ve had that cancer has taken, and probably not the last. I had a pit/boxer mix die from transitional cell cancer of the bladder in 2008 and I just found out my 12 yr old male doxie’s osteochondrosarcoma has returned in his jaw- it was successfully removed in early 2018. I am SO sick of cancer killing my dogs/animals and the PEOPLE we love too. It feels like it has become an epidemic!

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