Mast Cell Tumors in Cats: Symptoms, Sites, and Prognosis
By Dr. Zubair Khalid, DVM, MS, PhD ·
Most mast cell tumors in cats are skin tumors that behave in a benign way, and many cats do well after surgery alone. The same tumor in the spleen, intestine, or lymph nodes is a different problem, with a more guarded outlook and a need for staging tests. This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- A mast cell tumor in cats is most often a skin lump, and these tumors typically behave in a clinically benign way [1].
- Multiple skin tumors, tumors that come back, or spread to lymph nodes point to a more guarded prognosis [1].
- A fine needle aspirate lets your veterinarian look at the cells, and a biopsy confirms the type and whether the whole tumor was removed [2].
- Surgery is the treatment of choice for skin tumors, and other options exist when tumors are large or numerous [1].
- Tumors in the spleen, gut, or lymph nodes need staging and a different treatment plan than a simple skin lump.
What Is a Mast Cell Tumor in Cats?
A mast cell tumor is a growth made of mast cells. Mast cells are normal immune cells that live in your cat's skin, gut, and other tissues. When these cells multiply out of control, they form a tumor.
Tumors can be benign or malignant. Benign tumors do not invade tissue or spread to other parts of the body, and they are easy to remove with surgery. Malignant tumors can invade nearby tissue and spread to distant organs [2]. Telling the two apart takes laboratory testing, not just a look or a feel [2].
In cats, the skin form is one of the most common skin tumors, and it usually behaves in a clinically benign way [1]. That is good news for most owners. The catch is that mast cell tumors can also start in places you cannot see, like the spleen, the intestine, or a lymph node. Where the tumor starts changes everything about symptoms, testing, and outlook.
Signs Owners Notice
Skin Tumors
Skin tumors show up as lumps or bumps you can feel. They may be small and firm, or soft and movable. Some cats have one lump. Others have many. In one report, three cats had between 7 and 50 nodules, each measuring 0.2 to 1 cm, spread over the head and trunk [1]. Another cat had a single large tumor on the head measuring 4.6 cm [1].
Many skin mast cell tumors cause no obvious discomfort. Some cats lick or scratch at the spot. A tumor in an unusual place, like the ear canal, can cause itching, bleeding, or a mass that looks like a polyp [3].
Spleen Tumors
A tumor in the spleen often causes vague signs. Your cat may eat less, lose weight, or seem tired. The spleen can enlarge, and in some cases it can bleed. These signs are easy to miss at home.
Intestinal Tumors
A tumor in the intestine can cause vomiting, diarrhea, poor appetite, and low energy. One 15-year-old cat with a mast cell tumor in the jejunum (part of the small intestine) came in with vomiting, diarrhea, anorexia, and lethargy [4]. Imaging showed diffuse thickening of the intestinal wall and a focal lesion with loss of normal wall layering [4].
Lymph Node Tumors
When mast cell tumors reach lymph nodes, the nodes may swell. This can happen with skin tumors that spread, or as part of more widespread disease. Spread to lymph nodes is linked to a more guarded prognosis [1].
Causes and Risk Factors
We do not know exactly why most cats develop mast cell tumors. Age matters. The cats in reported cases were 8, 12, 15, and 16 years old [5][3][4][6]. Older cats are more often affected.
Site matters too. Skin tumors are common and usually calm. Tumors in the gut, spleen, or lymph nodes behave more aggressively. Some microscopic features also matter. A tumor with epitheliotropism, meaning the tumor cells move into the surface layer of the skin, may follow a more aggressive course [6]. That finding is uncommon and needs more research before we can predict outcomes well [6].
Breed and sex may play a role, but the evidence in cats is thin. One case involved a castrated male Korean Shorthair [5], another a male domestic medium-hair [6], and another a neutered male European Shorthair [3]. These single cases do not prove a pattern. If your cat has a lump, the lump itself matters more than the breed label.
How Mast Cell Tumors in Cats Are Diagnosed
Fine Needle Aspirate and Cytology
The first step is often a fine needle aspirate. Your veterinarian puts a thin needle into the lump, pulls out some cells, and looks at them under a microscope [2]. This is quick and usually done in the clinic. Mast cell tumors in cats can be harder to identify on cytology than in dogs because the cells may have fewer granules. That is why cytology is a starting point, not the final word.
Biopsy and Margins
A biopsy removes a piece of tissue for laboratory evaluation [2]. After surgery, the removed tumor should go to a lab to confirm the type and to check whether the whole tumor was likely removed. The lab looks at the edges of the tissue, called margins. Dirty margins mean tumor cells reach the edge, so cells likely remain in your cat. Narrow margins mean cells are close to the edge, so some could be left behind. Wide or clean margins mean cells are far from the edge, so it is unlikely any remain [2].
Staging Tests
Staging looks for spread. This may include blood work, ultrasound of the liver and spleen, and sampling of lymph nodes [3]. Your veterinarian may also check the gut if your cat has digestive signs. Staging tells you whether the tumor is in one spot or has moved, and that changes the plan.
A Note on Cytology
Cytology is a skill, and reading skin masses takes practice. If you want to understand how veterinarians sort through cell samples from lumps, see Decoding the Cytology of Canine and Feline Cutaneous Masses. It explains the decision steps behind the report you get.
Treatment Options
Surgery
Surgery is the treatment of choice for skin mast cell tumors [1]. Your veterinarian removes the lump and sends it to a lab. If margins are clean, that may be all your cat needs. If margins are dirty or narrow, a second surgery or another treatment may be discussed [2].
When Surgery Is Hard
Multiple or large tumors can make surgery difficult [1]. In those cases, other local or systemic treatments may help. Electrochemotherapy with intravenous bleomycin was used in four cats with skin tumors, and all tumors resolved completely [1]. That dose was calculated per body surface area by the treating team, and your veterinarian would decide whether such a treatment fits your cat.
Medical Therapy
Toceranib phosphate is a drug option for some skin tumors. In one cat with multiple skin tumors, toceranib led to clinical improvement and a strong partial response, though the tumor progressed 13 weeks later and the cat was switched to lomustine [6]. That cat was euthanized 11 days after the switch [6]. This is one case, not a rule, but it shows why follow-up matters.
Intestinal and Spleen Tumors
Tumors in the gut often need surgery to remove the affected segment. One cat with a jejunal mast cell tumor and a second cancer in the same area had the segment removed and was treated with chlorambucil [4]. Treatment plans for internal tumors are built case by case.
Recovery, Outlook, and Long-Term Management
Skin Tumors
Most skin mast cell tumors in cats behave in a benign way, and many cats do well after surgery [1]. The outlook is less favorable when there are multiple tumors, when tumors come back, or when lymph nodes are involved [1]. Some microscopic patterns, like epitheliotropism, may also signal a more aggressive course [6].
Spleen and Gut Tumors
These tumors carry a more guarded outlook than skin tumors. They are often found later, and they can cause internal bleeding or block the gut. Staging and early treatment give your cat the best chance.
Ear Canal and Other Odd Sites
A mast cell tumor in the ear canal is rare but possible [3]. One cat had the ear canal removed, and the margins were free of tumor cells [3]. That cat was euthanized 14 months after surgery, and it is unknown whether the original tumor had spread [3]. Rare sites mean less data, so your veterinarian will rely on staging and margin results.
Follow-Up
Plan on regular rechecks. Your veterinarian will feel for new lumps, check old surgery sites, and may repeat imaging or blood work. Report any new lump, weight loss, vomiting, or change in appetite right away. Keep a simple log of your cat's weight and appetite. Small changes are easier to spot when you track them.
A Related Condition to Know
Cats with skin or gut tumors sometimes have other immune-related problems. If your cat has raised, inflamed skin lesions, see Eosinophilic Granuloma In Cats: Comprehensive Veterinary Reference Guide. If your cat has trouble breathing, see Cat Asthma: Signs, Diagnosis, and Long-Term Veterinary Management. Breathing changes in a cat with cancer always need prompt care.
Site Comparison at a Glance
| Site | Common signs | Typical behavior | Main treatment |
|---|---|---|---|
| Skin | Lump or lumps, sometimes itching | Often clinically benign [1] | Surgery [1] |
| Spleen | Weight loss, tiredness, possible bleeding | More guarded | Staging, surgery, medical therapy |
| Intestine | Vomiting, diarrhea, poor appetite [4] | More guarded | Surgery to remove the segment [4] |
| Lymph nodes | Swollen nodes | More guarded [1] | Staging, systemic therapy |
Prevention
There is no proven way to prevent mast cell tumors in cats. The best you can do is catch them early. Feel your cat's skin during quiet moments. Run your hands along the legs, belly, head, and tail. Check the ears, including the canal opening, since tumors can hide there [3].
Book a veterinary visit for any new lump that lasts more than a few weeks, grows, changes, or bothers your cat. Early removal gives the lab a clean sample and gives you clear information [2]. Keep up with routine exams, especially as your cat gets older. Most reported cases involve cats in their senior years [5][6][3][4].
Limitations and When to Contact a Veterinarian
This article cannot tell you what your cat's tumor will do. Only your veterinarian, with the cytology or biopsy report and staging results, can do that. Individual cases need a veterinarian.
Contact your veterinarian the same day if you find a new lump that is growing fast, bleeding, or oozing, or if your cat stops eating or starts vomiting.
Go to an emergency clinic now if your cat has trouble breathing, pale gums, a swollen belly, collapse, or severe weakness. These can signal internal bleeding or another urgent problem.
Schedule a routine visit if you find a small, stable lump, or if your cat has a slow change in appetite or weight. Bring a note of when you first felt the lump and whether it has changed.
Frequently Asked Questions
Are mast cell tumors in cats usually cancer?
Most skin mast cell tumors in cats behave in a benign way, even though the name sounds alarming [1]. That said, some are malignant and can spread, especially when they start in the spleen, gut, or lymph nodes. The only way to know which type your cat has is through laboratory testing [2].
Can a mast cell tumor in cats be cured?
Many skin tumors are cured with surgery alone when the whole tumor is removed with clean margins [2][1]. Tumors in internal organs are harder to cure, and treatment aims to control the disease and keep your cat comfortable. Your veterinarian will set expectations based on the biopsy and staging results.
How long can a cat live with a mast cell tumor?
Life expectancy depends on the site and the stage. One cat with an ear canal tumor lived 14 months after surgery [3]. Another cat with multiple skin tumors responded to treatment for about 13 weeks before the tumor progressed [6]. These are single cases, so ask your veterinarian for an estimate based on your cat's specific report.
Does a mast cell tumor in cats spread to other organs?
Skin tumors in cats often stay local, but spread to lymph nodes is possible and points to a more guarded prognosis [1]. Tumors that start in the spleen or gut can spread more readily. Staging tests are how your veterinarian checks for spread [3].
What does cytology show for a mast cell tumor in cats?
Cytology shows the cells pulled from the lump with a fine needle [2]. Mast cells in cats can be hard to identify because their granules may be sparse, so the report may say "suspicious" instead of giving a firm answer. A biopsy is often needed to confirm the diagnosis and check the margins [2].
Related Articles
- Feline Feline Mammary Tumors: Diagnosis and Management
- Eosinophilic Granuloma In Cats: Comprehensive Veterinary Reference Guide
- Cat Asthma: Signs, Diagnosis, and Long-Term Veterinary Management
- Decoding the Cytology of Canine and Feline Cutaneous Masses
- Feline Macrophage Activation Syndrome: Diagnosis and Management
- Feline Hyperthyroidism: Signs, Diagnosis, and Treatment
References
- Successful treatment of cutaneous mast cell tumors in cats using electrochemotherapy: A case series. Open veterinary journal, 2025.
- Tumors of the Skin in Cats - Cat Owners. Merck Veterinary Manual.
- Unusual presentation of a mast cell tumor in the ear canal of a cat. Tierarztliche Praxis. Ausgabe K, Kleintiere/Heimtiere, 2024.
- Synchronous Low-Grade Alimentary Lymphoma and Gastrointestinal Mast Cell Tumor with a Collision Pattern in a Cat. Veterinary sciences, 2026.
- Feline cutaneous mast cell tumor with extensive macrophage-associated cell-in-cell structures. Journal of veterinary diagnostic investigation : official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc, 2026.
- Multiple cutaneous mast cell tumors displaying epitheliotropism in a male cat. The Canadian veterinary journal = La revue veterinaire canadienne, 2025.