Mast Cell Tumors in Cats vs Dogs: Key Differences
By Dr. Zubair Khalid, DVM, MS, PhD ·
Mast cell tumors in cats vs dogs behave very differently, even though both species get the same type of tumor. In dogs, most mast cell tumors are skin tumors that can range from harmless to aggressive. In cats, skin mast cell tumors are often slow-growing, but cats also develop a separate intestinal form that can be serious. This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- In dogs, mast cell tumors are one of the most common skin tumors and are graded by how aggressive the cells look, which guides treatment.
- In cats, most skin mast cell tumors are benign or low grade and behave differently from the dog version.
- Cats can also develop visceral (internal) mast cell tumors, especially in the spleen and intestine, and these can be harder to detect early.
- Diagnosis in both species usually starts with a fine needle aspirate, then a biopsy for grading and margins.
- Treatment depends on location, grade, and whether the tumor has spread, so your vet will tailor the plan to your pet.
What Is a Mast Cell Tumor in Plain Words?
A mast cell tumor (MCT) is a cancer made of mast cells. Mast cells are immune cells that normally live in your pet's skin, gut, and other tissues. They help with allergic reactions and inflammation. When these cells grow out of control, they form a tumor [1][2].
Mast cell tumors can appear in the skin (cutaneous) or inside the body (visceral). In dogs, cutaneous MCTs are common and can show up almost anywhere on the body. In cats, cutaneous MCTs are also seen, but they tend to behave differently. Cats also get visceral MCTs, especially in the spleen and gastrointestinal tract, and these are a distinct concern [3][4].
The key point for owners is this: a mast cell tumor diagnosis in a dog does not mean the same thing as it does in a cat. The location, grade, and species all change the picture.
Signs Owners Notice: Feline vs Canine Mast Cell Tumor Behavior
What dog owners see
In dogs, a mast cell tumor often looks like a raised lump or bump on or just under the skin. Some dogs have one lump. Others have several. The lump may be hairless, red, or itchy. Some dogs scratch or lick at it because mast cells release histamine and other chemicals that cause inflammation.
Canine mast cell tumors can also change size quickly. A lump that seems small one week may look bigger the next. That fluctuation is one reason vets recommend checking any new lump. If your dog has a lump and you are not sure what it is, this guide on why dogs get lumps and how vets tell lipomas from mast cell tumors and cysts can help you understand the next steps.
What cat owners see
In cats, cutaneous mast cell tumors often look like small, firm, raised bumps on the skin. They may be hairless or have a crusty surface. Many cats have just one or a few. Feline skin MCTs often grow slowly and may not bother the cat at all.
Cats can also get mast cell tumors in less common places. One report described a low-grade mast cell tumor in the ear canal of a 12-year-old cat that caused itching and bleeding [5]. That is rare, but it shows that MCTs can appear in unexpected spots.
Visceral mast cell tumors in cats are different. They can cause weight loss, vomiting, diarrhea, or a swollen abdomen. Some cats with intestinal MCT also have a second cancer called low-grade alimentary lymphoma at the same time [3][4]. That combination is being recognized more often in cats.
Causes and Risk Factors
The exact cause of mast cell tumors is not fully understood in either species. In dogs, certain breeds (Boxers, Boston Terriers, Pugs, and others) are known to develop MCTs more often. Genetics likely play a role.
In cats, no single breed or virus has been clearly linked to mast cell tumors the way feline leukemia virus and feline immunodeficiency virus are linked to lymphoma [1]. Some reports describe MCTs in unusual species, including a meerkat and a spiny mouse, which shows that these tumors can occur across many mammals [6][7]. That does not change how we treat your pet, but it does show that mast cell biology varies widely.
Age matters. Most mast cell tumors are diagnosed in middle-aged to older pets. But young animals can develop them too.
How Mast Cell Tumors Are Diagnosed
Fine needle aspirate
The first step is usually a fine needle aspirate (FNA). Your vet inserts a thin needle into the lump, collects a few cells, and looks at them under a microscope. Mast cells have distinctive granules that often make them easy to identify. This test is quick, minimally invasive, and often done in the exam room.
If your vet wants more detail on how cytology fits into the diagnostic process, this article on decoding cytology of cutaneous masses explains the decision tree. For a broader look at when vets choose FNA versus biopsy, see FNA vs biopsy in pets.
Biopsy and grading
If the aspirate suggests a mast cell tumor, your vet will likely recommend a biopsy. A biopsy gives the pathologist a full piece of tissue to examine. That is how the tumor gets graded.
Grading is a big difference between dogs and cats. In dogs, MCTs are typically graded as low grade or high grade (or using a two-tier or three-tier system). The grade predicts how aggressive the tumor is likely to be. In cats, cutaneous MCTs are often described differently, and many are low grade or benign. The grading schemes are not identical between species.
For a deeper dive into canine grading and treatment, see mast cell tumors in dogs: grading and treatment guide.
Staging
Staging means checking whether the tumor has spread. In dogs, this may include blood work, imaging, and lymph node sampling. In cats with visceral MCT, staging often includes ultrasound of the liver and spleen, plus a complete blood count [5]. Your vet will decide which tests are needed based on the tumor location and your pet's overall health.
How Treatment Differs Between Cats and Dogs
| Feature | Dogs | Cats |
|---|---|---|
| Most common location | Skin (cutaneous) | Skin (cutaneous), also spleen and intestine |
| Typical behavior | Variable, some aggressive | Often slow-growing when on skin |
| Grading system | Well established, guides treatment | Different criteria, often low grade |
| Surgery | Common first treatment | Common first treatment |
| Chemotherapy | Used for high-grade or spread | Used for visceral or aggressive cases |
| Prognosis | Depends heavily on grade | Skin form often good, visceral form more guarded |
Surgery
Surgery is the main treatment for most cutaneous mast cell tumors in both species. The goal is to remove the tumor with a margin of normal tissue around it. In dogs, vets often take wide margins because MCTs can send out microscopic tendrils. In cats, margins may be smaller for low-grade skin tumors, but your vet will still aim for clean edges.
One cat with an ear canal MCT had total ear canal ablation, and the surgical margins were free of tumor cells [5]. That cat was euthanized 14 months later, but it is unknown whether the original tumor spread [5]. That case shows that even rare locations can be treated surgically.
Chemotherapy and other drugs
If a mast cell tumor is high grade, has spread, or cannot be fully removed, your vet may recommend chemotherapy or other medications. In dogs, drugs like vinblastine, lomustine, and tyrosine kinase inhibitors are sometimes used. In cats, chemotherapy is used more often for visceral MCT or when the tumor behaves aggressively.
Your veterinarian calculates the dose from your pet's weight and health. Never give human medications or leftover pet medications without veterinary guidance.
Radiation therapy
Radiation can be used when surgery does not get clean margins or when the tumor is in a spot that is hard to operate on. Not every clinic offers radiation, so your vet may refer you to a specialty center.
Recovery, Outlook, and Long-Term Management
Dogs
The outlook for a dog with a mast cell tumor depends mostly on the grade. Low-grade tumors that are completely removed often have a good long-term outlook. High-grade tumors or those that have spread need more aggressive treatment and carry a more guarded prognosis.
Your vet will likely recommend rechecks every few months after surgery. They will feel the surgery site and check for new lumps. Some dogs need blood work or imaging to watch for spread.
Cats
For cats with cutaneous mast cell tumors, the outlook is often good if the tumor is low grade and removed completely. Many cats do well for years.
For cats with visceral MCT, the outlook is more variable. Intestinal MCT can cause vomiting, diarrhea, weight loss, and lethargy [3]. Some cats with intestinal MCT also have low-grade alimentary lymphoma, and that combination can affect treatment decisions [4]. Your vet may recommend surgery, chemotherapy, or both.
Long-term management for any pet with MCT includes regular veterinary visits, monitoring for new lumps, and watching for changes in appetite, energy, or digestion. If your cat has a history of mammary tumors, this article on feline mammary tumors covers another cancer that can affect cats.
Prevention
There is no proven way to prevent mast cell tumors in cats or dogs. You cannot vaccinate against them or change your pet's diet to eliminate the risk.
What you can do is pay attention. Check your pet's skin regularly. Feel for new lumps, bumps, or swellings. If you find something, have your vet look at it. Early detection often makes treatment easier.
For cats, watch for vomiting, diarrhea, weight loss, or a swollen belly. Those signs can point to visceral tumors. For dogs, watch for lumps that change size, become red or irritated, or bother your dog.
Limitations and When to Contact a Veterinarian
This article gives general information. Your pet's individual case needs a veterinarian who can examine the tumor, review the biopsy, and recommend treatment.
Contact your vet the same day if:
- Your pet has a lump that has grown quickly over a few days.
- A lump is bleeding, oozing, or has an open sore.
- Your pet is scratching or biting at a lump until it is raw.
Go to an emergency clinic now if:
- Your pet has trouble breathing, collapses, or has a swollen abdomen that came on suddenly.
- Your pet is vomiting repeatedly and cannot keep water down.
- Your pet has pale gums, weakness, or seems painful when you touch the belly.
Schedule a routine visit if:
- You find a new lump or bump on your pet's skin.
- Your pet has a lump that has been there for weeks without changing.
- Your cat has chronic vomiting, diarrhea, or weight loss.
Frequently Asked Questions
Are mast cell tumors more serious in cats or dogs?
It depends on the type. In dogs, mast cell tumors are common and can range from mild to aggressive, so the grade matters a lot. In cats, skin mast cell tumors are often low grade and slow-growing, but visceral tumors in the spleen or intestine can be more serious.
Can a cat live a normal life with a mast cell tumor?
Many cats with a low-grade skin mast cell tumor live a normal life after surgery. The tumor is often cured with complete removal. Cats with visceral mast cell tumors may need more treatment and monitoring.
Do mast cell tumors in dogs spread quickly?
Some do and some do not. Low-grade tumors often stay local, while high-grade tumors can spread to lymph nodes, the spleen, or other organs. Your vet uses the biopsy grade and staging tests to estimate the risk.
What questions should I ask my vet after a mast cell tumor diagnosis?
Ask what grade the tumor is, whether the margins were clean, whether staging tests are needed, and what treatment options are available. Also ask how often your pet needs rechecks and what signs to watch for at home.
Is a mast cell tumor in a cat's intestine the same as one on the skin?
No. Intestinal mast cell tumors in cats are visceral tumors and behave differently from skin tumors. They can cause vomiting, diarrhea, and weight loss, and they may occur alongside another cancer called low-grade alimentary lymphoma. Treatment usually involves surgery and sometimes chemotherapy.
Related Articles
- Mast Cell Tumors in Dogs: Histopathological Grading and Treatment Guide
- Why Is My Dog having lumps on skin? Lipoma vs Mast Cell vs Cyst Diagnosis
- Feline Feline Mammary Tumors: Diagnosis and Management
- Decoding the Cytology of Canine and Feline Cutaneous Masses
- Fine Needle Aspirate FNA vs Biopsy in Pets: Cancer Diagnosis Protocol
- Feline Leukemia FeLV and FIV Testing: Snap Tests vs PCR Differences
- Mast Cell Tumors in Cats: Symptoms, Sites, and Prognosis
- Zyrtec for Dogs With Mast Cell Tumors: Does It Help?
- Fatty Lump or Tumor? Lumps and Weight Loss in Dogs
- Fine-Needle Aspirate Cytology of Cutaneous Mast Cell Tumors
References
- Immune System Tumors in Cats - Cat Owners. Merck Veterinary Manual.
- Immune System Tumors in Dogs - Dog Owners. Merck Veterinary Manual.
- Synchronous Low-Grade Alimentary Lymphoma and Gastrointestinal Mast Cell Tumor with a Collision Pattern in a Cat. Veterinary sciences, 2026.
- Standardized classification of synchronous gastrointestinal small cell lymphoma and gastrointestinal mast cell tumors in 15 cats. Journal of feline medicine and surgery, 2025.
- Unusual presentation of a mast cell tumor in the ear canal of a cat. Tierarztliche Praxis. Ausgabe K, Kleintiere/Heimtiere, 2024.
- Cutaneous Mast Cell Tumor With Metastasis in a Pet Cairo Spiny Mouse (Acomys cahirinus): A Case Report With Clinicopathologic Characterization. Case reports in veterinary medicine, 2026.
- Case Report: Clinicopathological findings of a cutaneous mast cell tumor in a young domestic meerkat (Suricata suricatta). Frontiers in veterinary science, 2025.