paw and hand reaching out

Help For A Dog With Mast Cell Tumor

When I found a seemingly innocent-looking lump on my Cocker Spaniel’s shoulder blade, I was shocked to receive a mast cell tumor diagnosis. If you are reading this post, your dog has likely been diagnosed with a mast cell tumor or you want to learn more about mast cells and what causes these tumors.

Often dubbed the “great imposters,” canine mast cell tumors can look like an ordinary lump, wart, or growth on a dog’s skin, but they must be addressed as soon as possible. If you have a dog with mast cell tumor (MCT) as a confirmed diagnosis, there are several options. When MCTs appear on a dog’s skin, they vary immensely in appearance. They can be raised on top of the skin or be red, ulcerated, and swollen.

Prognosis and treatment of mast cell tumors include surgery, radiation therapy, chemotherapy, drug therapy, and/or a new form of treatment called Stelfonta, an intratumoral treatment for this very common form of skin cancer in dogs. Lumps and bumps on dogs are very common, and no one, including veterinarians, can diagnose a dog lump without aspiration or biopsy.

Cancer is a scary six-letter word, and millions of dogs are diagnosed every single year. Since mast cell tumors vary widely in their size, shape, appearance, texture, and location, it is important to be the aggressor and not let cancer take hold of your dog.

In this article, I’ll share my dog’s journey with a mast cell tumor along with survival tips, what the experts say, how mast cell tumors are diagnosed, and the latest innovations and treatments to help your dog.

cute cocker
Forever missed, Brandy Noel.

My Dog’s Journey With A Mast Cell Tumor

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

Cancer. I will never forget my Cocker’s Spaniel’s veterinarian calling me to tell me my dog had a mast cell tumor and we needed to get aggressive about treatment. It all started with a small wart-like lump on her right shoulder blade, which appeared within two weeks after then-yearly vaccinations.

My dog’s veterinarian at the time tried to “squeeze” the lump and said it was probably nothing more than a pimple or sebaceous cyst. He was dead wrong. The C Word. You could have knocked me over with a feather.

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

Brandy was my first Cocker Spaniel and her mast cell journey included:

  • Bloodwork
  • Laser surgery showed clean margins so a second procedure was not needed.
  • Abdominal ultrasounds to check for metastases every three months for one year and then every six months in year two at Cornell University’s Oncology Department. Our 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.
  • Buffy coat bloodwork
  • Regular measurement and aspiration or biopsy of all new lumps and bumps

What Is A Canine Mast Cell Tumor?

Mast cells develop from cells within the immune system. They are found in connective tissue and carry histamine and heparin in small granules. Humans have mast cells, too.

If a dog has an allergic reaction, mast cells get to work. Think of when a foreign invader comes at the body: Histamines flare up and the mast cells serve to modify the immune reaction. Just like other cells in the body, mast cells can divide rapidly and form a tumor. Mast cell tumors are one of the most common types of skin cancer in dogs.

According to the Michigan State University Veterinary Diagnostic Laboratory, it is not yet known why MCTs are more prevalent and malignant in dogs versus other animal species.

Sometimes MCTs will bigger and smaller due to the histamine getting released into local tissues and getting reabsorbed. Since heparin can get released as well, MCTs can bruise since heparin is a blood thinner. So if a growth appears on your dog’s skin, be sure not to wait and see the veterinarian. MCTs can be tricky!

What Do Mast Cell Tumors Look Like?

Mast cell tumors look like anything and everything. Dr. Sue Ettinger, the “Cancer Vet” says MCTs account for 15 to 20 percent of all skin cancers in dogs. Some MCTs are very benign despite their malignant nature and others are much more aggressive. Dr. Sue calls them “treatable tumors,” and this is something to remember as your dog faces treatment.

MCTs can have a variety of appearances. Washington State University’s Oncology Service says MCTs can look like just about anything from a benign-appearing lipoma to an angry-looking mass with thickness.

lumps on a dog's body
Various lumps on dogs.

What To Do If You Find A Lump On Your Dog

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.

Here’s what to do if your dog has a new lump or bump:

  • 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.
  • 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 back in the 1990s. These days, you can get calipers on Amazon or digital calipers from Dr. Sue Cancer Vet’s website. Calipers minutely measure the width of a lump. Document it. Monitor the lump for any sign of growth or physical change. See the veterinarian.
  • Document any changes, new lumps, and locations on the body in our DogMinder Canine Health & Wellness Journal.
  • DON’T squeeze any lump or bump on a dog’s skin, as 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, but we caught it.
  • Print copies of skin maps and document each new growth and location.
  • Know the warning signs of canine cancer.

How Are Mast Cell Tumors Diagnosed In Dogs?

A true diagnosis can never be confirmed without diagnostic evaluation through a fine-needle aspiration or a biopsy of the suspicious mass. Even after many benign aspirations, any new mass can be malignant. Early detection is crucial.

Some vets will rush and want to remove a mass right away, which is not always a viable option. Many veterinary oncologists agree that aspiration is generally advised before a mass is removed. If the mass is not an MCT and turns out to be something even more aggressive, you’ll have a baseline diagnosis and can proceed with a plan.

Dr. Sue Ettinger is a practicing veterinary cancer specialist and says, “No, not even the most experienced veterinarian can look at or feel a mass and know if it is cancer or not. Your veterinarian must perform an aspirate or biopsy to make an accurate diagnosis.”

Pros of Fine Needle Aspiration

  • Performed in office
  • Quick test
  • No need for sedation or hospitalization
  • Helpful in diagnosing the type of growth (i.e. mast cell, lipoma, cyst)
  • Noninvasive

Drawbacks of Fine Needle Aspiration

  • FNA cannot ascertain if cancer has spread to other areas of the body
  • Very occasional inconclusive or incorrect diagnosis with fine needle aspiration
dog with mast cell tumor
Dexter is a very good boy.

How Serious Are Mast Cell Tumors?

Mast cell tumors are divided into three grades. with grade I being the least aggressive and least likely to spread to other organs. Grade III is considered a highly aggressive MCT with a high likelihood of metastasizing to other organs.

Grade II MCTs tend not to metastasize, although they can. My Cocker Spaniel’s grade II mast cell tumor never spread to her other organs. In the event of spread, MCTs tend to affect the liver, spleen, bone marrow, and regional lymph nodes.

MCTs are a form of cancer, so they are serious and should be examined and treated as deemed necessary according to the grade, prognosis, and overall health and well-being of the dog.

A new two-tiered histologic grading system has been established in recent years. According to the two-tiered system, high-grade mast cell tumors are significantly associated with shorter time to metastasis or new tumor development and with shorter survival time. It’s called the high-low grading system and has improved the way mast cell tumors are graded.

What Are The Symptoms Of A Mast Cell Tumor?

Many times a dog will have no symptoms of mast cell tumor, but symptoms can be dependent on the grade and location of the tumor. Some symptoms include but are not limited to:

  • Tumor on or under the skin which may or may not appear to change in size
  • Possible lymph node enlargement
  • Vomiting
  • Loss of appetite
  • Diarrhea
  • May be a single growth or multiple masses throughout the body
  • May resemble an insect bite, wart, allergic reaction, or innocent-looking growth
  • May appear red and angry with fluid build-up
  • Tends to occur in middle-aged and older dogs (per Dr. Sue Ettinger)

Causes and Prevention Of MCTs In Dogs

What causes MCTs in dogs?

Like most tumors, the exact cause is not known. About one-third of dogs have a genetic mutation in a protein called the c-kit oncogene. Unlike skin cancer in humans, which is often associated with sun exposure, studies have found no link between sun exposure and MCT in dogs. But chronic inflammation of the skin may predispose dogs to develop MCT, as can the repeated application of skin irritants.

Dr. Sue Ettinger

My Cocker Spaniel’s mast cell tumor appeared at the site of her vaccinations. She received her then-yearly vaccines, and the vet gave her multiple vaccines in one spot (not the rabies vaccine). There is something called vaccine-associated sarcoma.

Brandy was firmly diagnosed with a mast cell tumor, grade II, at the site of her vaccine injections.

Certain breeds of dogs are more highly represented than others, and the University of Penn cites Boston Terriers, Boxers, Pugs, Bulldogs, and Retriever breeds. However, any dog whether purebred or mixed breed can develop MCTs.

One of the best ways to ensure your dog remains a loving, loyal part of the family for a long time is to touch him or her. 10 touches, 10 minutes, once a week will keep a dog healthy, happy, and rewarding you with love. Learn more about 10 touches to keep a dog healthy.

adorable cocker spaniel looks at his mom
Mayor is a survivor!

Dedicated dog mom Nancy B. of Maryland regularly runs her fingers through her Cocker Spaniel’s coat on a regular basis. She touches Mayor’s skin and examines his body, armpits, belly, and gives him a thorough “once-over.”

Thanks to Nancy’s due diligence, twice she found small lumps on her dog and twice they have been removed. Mast cell tumor was the diagnosis both times, and surgery was curative for his stage II tumors.

Can Lipomas Become Mast Cell Tumors?

“In general things like lipomas don’t morph into mast cell tumors,” according to Dr. Ettinger.

Some lipomas, she says, should be removed. For example, if a lipoma hinders mobility, is located in an armpit and becomes ulcerated, or if the dog licks at it. Once a lipoma grows larger, it can become challenging.

She says if a veterinarian aspirates a lump and confirms it is a lipoma at 3-cm, but perhaps six weeks later the lump doubled in size, it’s time for a return visit. She recommends having the vet biopsy the lipoma, as cytology isn’t always perfect.

How Are Mast Cell Tumors Treated?

Once a fine-needle aspiration or biopsy has confirmed the diagnosis, treatment for MCTs includes surgery, radiation, chemotherapy, drug therapy, or Stelfonta, a new FDA-approved intra-tumoral injection for the treatment of non-metastatic cutaneous mast cell tumors and non-metastatic subcutaneous mast cell tumors located at or distal to the elbow or the hock in dogs.


Wide margins of normal tissue must be excised around the to increase the likelihood that the tumor is completely removed. Surgical removal is a staple treatment for many canine mast cell tumors. Periodic monitoring is key for dogs with low-grade to intermediate MCTs for which surgery is curative.

If mast cell tumors are unable to be completely resected, could not be removed, or are not amenable to treatment with Stelfonta, radiation therapy is often performed. Sometimes a second surgical procedure is performed.

Radiation or Chemotherapy

Dogs with more aggressive tumors, such as grade III, may undergo chemotherapy. The Washington State Veterinary Teaching Hospital’s Oncology Service says mast cell tumors are unpredictable with their reaction to chemotherapy.

Drug Therapy

If the pathologist or veterinary oncologist chooses to have an MCT prognostic panel performed, results will show if there is a mutation in a gene called c-Kit. Dogs may be eligible for targeted drug therapy with Palladia (toceranib phosphate) and Kinavet-CA1 (masitinib mesylate).


According to Dr. Ettinger, Stelfonta is injected directly into the mast cell tumor. Although this treatment won’t fully replace surgery to remove MCTs, Dr. Sue loves having Stelfonta as one of the tools in her MCT toolbox.

The success rate thus far has been promising, with a 75-percent response at day 28 after one injection. If a second injection is needed, the response rate goes up to 85 percent. At one year, 88 percent of treated dogs are disease-free. This is an exciting treatment that you can learn more about here:

What About Antihistamines To Treat Mast Cell Tumors?

I asked Dr. Patrick Mahaney, a University of Pennsylvania-trained veterinarian and Certified Veterinary Acupuncturist (CVA), if he knows of any pet parents who use antihistamines as a preventative option for MCTs.

“I’ve had patients take antihistamines once they’ve been diagnosed, but not before as a potential MCT preventative,” Mahaney says. “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.

He says putting a dog 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.

Dr. Ettinger says since histamine is in the mast cell tumors, the growths may appear red and inflamed as they grow on a dog’s skin.

“If a dog has a really big mast cell tumor, before surgery we will recommend that they go on an antihistamine,” she says.

For dogs with an MCT that cannot be removed, if radiation or chemo are used, she will keep them on an antihistamine. The reason she does this and may include an antacid like famotidine or omeprazole is the histamine causes increased stomach acidity and stomach upset.

She does not use antihistamines and antacids as a preventative, as there is no literature to her knowledge that using them will help prevent mast cell tumors.


What Is My Dog’s Prognosis?

Dr. Ettinger says mast cell tumors are treatable. Each requires different intensities of treatment depending on the grade. If the MCT is low grade and treatment is successful, she will usually see the patient once every three months for a while and then once every four to six months for life for screening.

If the tumor is a grade III and has spread to internal organs, she often sees the patients doing well after a year. She equates the one-year anniversary to a human cancer patient who is given a five- to seven-year survival prognosis. Like people, each dog is different.

We raise our sparkling water dish in a wish that your dog lives a life free of lumps and bumps. If your dog faces cancer at any point, be diligent and don’t panic. As your dog’s advocate and best friend, be the person your dog knows you are.

Help for mast cell tumors in dogs


  1. 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!

    1. My dog does have an in operable MCT on his penis he is a nine-year-old dog and surgery is out of the question what are things besides Benadryl I can do to ease his discomfort. He cannot tolerate prednisone gets immediately sick however he can take a shot in the butt

      1. Lisa, I would check with Dr. Sue Ettinger, aka Dr Sue the Cancer Vet. She has a lot of information on mast cell tumors. Look into Stelfonta.

  2. 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. 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. 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. 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.

    1. Thank you so much for writing this. My cocker spaniel just turned 4 last week and her surgery is tomorrow. It gives me hope.

  6. 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. 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. 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. 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!!

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

  10. 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. 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!

    1. 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. 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. 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. 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. 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. 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. 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

    1. My dog was just diagnosed and hers too isn’t operable and she’s 11 this month and I’m not doing amputation of her leg either which was a suggestion

      If you still have it I’d be interested in trying it on our sophie

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

  21. 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!

  22. Thank you for your article on Mast Cell Tumours. My elderly father has a 16 year old cairn dog who was diagnosed with a high grade grade 3 Mast Cell Tumour and had it removed surgically by our vet on 28th May 2020 , this cost almost £1000, he has no pet insurance and laid out a big chunk of what little savings he had. In September 2020 it returned and the vet said that it’ll cost the same again to remove it but this time he’s developed more lumps, the vet said that we have a number of options available to us, more surgery, just let him live in his home and to pass away peacefully, euthanasia or chemotherapy which will cost upwards of £3000, we are heartbroken as we are just basically waiting for this precious little dog to die, it’s not right that our pets have to die because we don’t have the money to pay for their treatment, my parents couldn’t afford to take out pet insurance as they were both pensioners when they got the dog whose name is Mac and their everyday bills were high-rent, council tax, gas, electricity, food bills etc-it’s been harder since my mother passed away 7 years ago and Mac was the dog she rescued from an addict and is now the last family pet connection to her, my father has got vascular dementia and Alzheimers and is brokenhearted that his faithful friend is going to be leaving him. The PDSA don’t treat dogs with cancer as the treatment is too costly. It’s now just a waiting game before Mac leaves us. I felt like I had to share our story as there are people up and down the UK who are in the same boat, I myself am on benefits so I couldn’t help out. The only thing I can say to anyone thinking about getting a pet, any pet that could be prone to lumps, cancers etc, please consider pet insurance as it will save you from so much heartache at the end of your furbabys life.

  23. I hate this disease. My dog had two grade II MCTs removed through surgery 9 months ago and she is recovering from having surgery to remove two more grade II MCTs right now. This surgery is hard! And incredibly expensive. I’ve put her I. High roses of vitamin C to strengthen her immune system. She’s a 10 year old rescue who has been an incredible delight to me.

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