Mast Cell Tumours In Dogs: What You Need To Know About!

Understand this common cancer and find inspiration in Pimmy's story. As a Mass Cell Tumour survivor, Pimmy shows us how early detection and the right care can make all the difference. Welcome!

What is a mast cell?

A mast cell is a type of white blood cell that is found in many tissues of the body. Mast cells are allergy cells and play a role in the allergic response. When exposed to allergens, mast cells release chemicals and compounds (called degranulation). One of these compounds is histamine. Histamine is commonly known for causing itchiness, sneezing, and runny eyes and nose – the common symptoms of allergies. When histamine and the other compounds are released in excessive amounts (with mass degranulation), it can cause full-body effects, including anaphylaxis, a serious, life-threatening allergic reaction. Other complications include delayed wound healing, bleeding disorders, and gastrointestinal (GI) ulceration.

This is me, Pimmy

"Right, my friends, listen up! Pimmy here! I'm sharing all the cool stuff I've learned on my wellness adventure! You know, I've been doing my homework – lots of internet digging and asking my awesome vet, Diana Weir D.V.M., right here at Merivale Papanui Vets in Christchurch! And guess what? I even got tips from my old vet, Dra. Analia Perez, from Clinica Veterinaria VET, back in Argentina! They helped me understand what these pesky mast cell tumours in dogs are and how to get better. But remember, every pup is unique! So, please, go see your vet! They'll know exactly what's best for your furry friend. I'm just sharing what helped me, hoping it can help you, too! Sending tons of tail wags and love!"

What is a mast cell tumour in dogs?

A Mast Cell Tumour (MCT) in dogs is a type of malignant (cancerous) tumour consisting of mast cells. Mast cell tumours typically form nodules or masses in the skin, but they can also affect other areas of the body, including the spleen, liver, intestine, and bone marrow. MCTS are the most common skin tumours in dogs (7%–21%). Most dogs with MCT (approximately 85%) only develop one tumour. MCTS can easily be mistaken for lipomas—a benign fatty tumour—so it’s important to have your veterinarian check out any lumps or bumps you find on your pet.

This was my vet measuring my MCT!

"So, you know, I had this little bump on my chest, right? Well, it wasn't so little! It was a mast cell tumour, they said. And even though it started out about the size of your tiniest fingernail, it grew to be around 4 centimetres! Can you believe it?"

Big question: What causes this cancer?

Why a particular dog develops MCTS or any cancer is not straightforward. Very few cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. Several genetic mutations are known to be involved in the development of MCTS. One well-known mutation affects a protein called KIT, which is involved in the replication and division of cells.

While any breed of dog can get MCT, certain breeds are more susceptible. MCTS are particularly common in boxers, English bulldogs, Boston terriers, pugs, golden retrievers, cocker spaniels, schnauzers, Staffordshire terriers, beagles, Rhodesian ridgebacks, Weimaraners, Chinese shar-peis, and Labrador retrievers. Affected dogs are usually older (average of 8–9 years); males and females are equally affected.

"Okay, so, guess what? This super cute pup right here on the left is a mix of Cocker Spaniel and Mini Golden Retriever! And get this, according to all the stuff my Mom and Dad have been reading, that means I'm one of those breeds that are more likely to get those pesky MCTS. Ugh, right? Pfff!"

What are the clinical signs of a mast cell tumour in a dog?

Mast Cell Tumours of the skin can occur anywhere on the body and vary in appearance. They can be a raised lump or bump on or just under the skin and may be red, ulcerated, or swollen. While some may be present for many months without growing much, others can appear suddenly and grow very quickly. Sometimes, they can suddenly grow quickly after months of no change. They may appear to fluctuate in size, getting larger or smaller, even daily. These size changes can occur spontaneously or when the tumour is agitated, which causes degranulation and subsequent swelling of the surrounding tissue due to the histamine release.

While some may be present for many months without growing much, others can appear suddenly and grow very quickly!

When mast cell degranulation occurs, some chemicals and compounds can go into the bloodstream and cause problems elsewhere. Ulcers may form in the stomach or intestines, causing vomiting, loss of appetite, lethargy, and melena (black, tarry stools that are associated with bleeding). Less commonly, these chemicals and compounds can cause anaphylaxis, a serious, life-threatening allergic reaction. Although very uncommon, MCTS of the skin can spread to the internal organs, causing enlarged lymph nodes, spleen, and liver, sometimes with peritoneal effusion (fluid build-up) in the abdomen, causing the belly to appear rounded or swollen.

"All right, pals, let me tell you, my Mom and Dad are the best! They're always giving me cuddles and pets, you know, touching me all over. And boy, am I glad they do! If they didn't, I might not have caught that sneaky little bump on my chest. They found it, and boom! Right to the vet at Merivale Papanui Vet! Seriously, thanks to them, I'm doing great! That's why I always talk about early detection; without it, my tumour wouldn't have been detected on time."

How is this cancer diagnosed in a dog?

This cancer is typically diagnosed using fine-needle aspiration (FNA). FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumour and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope. A tissue biopsy (surgically removed sample) can indicate how aggressive the tumour is, allowing your veterinarian to determine the best course of action. MCTS have been classically called “the great pretenders” because they may resemble an insect bite, wart, allergic reaction, or other less serious skin tumours. Therefore, any abnormalities of the skin that you notice should be evaluated by your veterinarian. Once a diagnosis of MCT has been made, your veterinarian or veterinary oncologist (cancer specialist) may recommend a prognostic panel on a tissue sample. This panel provides information on the genetic makeup and abnormalities of the tumour and provides valuable information that your veterinarian will use to determine the prognosis (the likely course of the disease) for your dog.

"Alright, so, get this! This nasty MCT was playing tricks on us! My vet took a peek and was like, "Oh, just a little fat bump! (called Lipomas). But, you know, my Mom and Dad, they wanted to be super sure! So, the doctor did this thing called FNA, a fine-needle aspiration. Basically, poked it and sent it to the lab. Now, we had to wait for the results, like forever- well, not that much, but it felt like that. Lol."

How does this cancer typically progress in a dog?

This tumour's behaviour is complex and depends on many factors. Typically, when a biopsy sample is examined under a microscope, the pathologist can assess how aggressive the cancer is based on several criteria. The whole tumour is graded from I to III, with Grade I being much less aggressive than Grade III. Higher-grade tumours have a higher tendency to metastasise (spread to other parts of the body).

Another classification system is also used to classify MCTS as either high-grade or low-grade. The average survival time with high-grade tumours is less than four months, and with low-grade tumours, it is more than two years.

Typically, the prognosis is less favourable if:

• The patient is one of the susceptible breeds,

• The MCT is located at a junction where the skin meets mucous membranes (e.g., the gums), or

• The number of cells actively replicating is high when viewed under the microscope.

"Ugh, you guys, this part is the worst. So, remember that little poke thing? The fine-needle aspiration (FNA)? Well, it hadn't even been a week, and my Mom got this super sad phone call. My vet was on the other end, and she said they had the results already. And guess what? Not good. I had an MCT on my chest. Mom was, like, totally heartbroken. She couldn't even hear what the vet was saying after that, except something about me... You know... I had to go for surgery and many more things about my condition. Pfff, just thinking about it gives me the creeps!"

How are mast cell tumours treated in a dog?

In lower-grade tumours with no evidence of spread, surgery is likely the best option. Surgery for lower-grade tumours provides the best long-term control, with chemotherapy rarely required. However, in higher-grade tumours, even without evidence of spread, a combination of surgery and chemotherapy is often recommended. Radiation therapy is another option if the mass is not in a suitable location for surgical removal or if the surgical removal is incomplete (with cancerous cells left behind).

"Okay, so, Mom was a total wreck! Dad had to ditch work and zoom over to the vet to double-check everything and figure out what to do next. They gave him all this paperwork for my surgery, and I was scheduled for the "big day" by the end of the week! And get this, I had to do all this pre-surgery stuff! No munchies after 7:00 pm the night before and barely any water after 7:00 am on surgery day! Then, they took my blood for tests before noon, and Mom and Dad had to wait until 4:00 pm to pick me up! Wow, talk about a wild ride!"

29th July 2024: Pimmy's mct's surgery day

Here I am after surgery!

"Okay, so, my surgery! Dr Tim Nottage B.VSc, a super cool vet surgeon from Merivale Papanui Vet, did it! He was so nice to my Mom and Dad, and he explained everything. He said the surgery went great! And get this, he thought the tumour was a Grade I, which is like, the least scary one! Thank goodness, right? But he did have to take out a lot of extra stuff around it, just to be safe. Now, we had to wait again, like, forever! Because they had to send a piece to the lab for a biopsy, and that takes about two weeks, because they don't do that stuff at the clinic. Phew, talk about waiting!..."

Is there anything else you should know?

You should avoid palpating (feeling) or manipulating the tumour (s), given how reactive MCT is, with degranulation easily triggered with pressure. Do not allow your dog to chew, lick, or scratch it, as this may also trigger degranulation. Degranulation may lead to further itchiness, swelling, discomfort, or even bleeding. Your veterinarian may recommend using an Elizabethan collar.

Important: Okay, pals, listen up! If you see a weird bump on your furry friend, paws off! Seriously, don't poke or mess with it too much. You could accidentally make it worse, like, trigger this thing called tumor degranulation, which is a big no-no! So, hands off, and let the vet take a look right away – no waiting here! The whole process depends on how quickly you get to the vet for help.

"All right, so after my surgery, I get to go home! They gave me these little pills, antibiotics and pain killers, to help me feel better. Lucky me, I didn't have to wear that cone thing because the bump was on my chest. Mom had to give me the pills on a super tight schedule, and I even had to wake up in the middle of the night! Now, if your pup is picky, I’m not, but I do love cheese! So, mom used cheese sticks to sneak the pills in, and I never even noticed! Clever, right? Anyway, later on, my vet said the biopsy was Grade I, just like they thought, and I was going to be fine! Yay! I hope sharing my story helps you and your furry friend if you ever have to deal with something scary like an MCT. It's tough, I know! But remember, seeing the vet right away is super important. And if you need surgery, you've got this! Stay strong, keep your tail up, and know you're not alone. Sending lots of love! - Pimmy."

♥♥♥♥

Sources: Information by VCA , Dog Cancer