Lumps on Your Cat’s Skin — Early Signs, Diagnosis, Treatment, and Prognosis Management of Mast Cell Tumors

Oncology/CancerDiseasesMeongsiljang Veterinary Advisory Board

Feline mast cell tumors are growths that can develop in the skin, spleen, or gastrointestinal tract, with prognosis and treatment options varying significantly depending on the type. Cutaneous (skin) mast cell tumors often have a high chance of cure with surgery, while visceral (internal organ) forms require prompt diagnosis and aggressive treatment to determine the outcome.

What Are Feline Mast Cell Tumors?

A veterinarian examining a cat — mast cell tumor screening

Feline mast cell tumors are a condition in which mast cells, which play a role in the immune response, abnormally proliferate in the skin, spleen, or gastrointestinal tract, forming tumors. They are the fourth most common skin tumor in cats (after basal cell tumors, fibrosarcomas, and squamous cell carcinomas) and also frequently occur in internal organs such as the spleen and gastrointestinal tract. The most important factor is the tumor’s location. Cutaneous (skin) mast cell tumors are mostly well-differentiated and benign; if detected early and completely surgically removed, they are often curable. In contrast, visceral forms occurring in the spleen or gastrointestinal tract have significantly different progression patterns and prognoses. Because symptoms can be vague, early detection is key.

Why Do They Occur? — Causes and Risk Factors

The exact cause of this condition remains unknown, but several risk factors have been identified.

Age: Cutaneous mast cell tumors primarily occur in middle-aged to senior cats, with a median age of approximately 10 years at diagnosis (though they can also develop in young cats).

Breed: Several breeds, including Siamese, Burmese, Maine Coon, Ragdoll, and Russian Blue, are at higher risk for mast cell tumors. Siamese cats, in particular, are strongly associated with atypical (histiocytic) cutaneous mast cell tumors that tend to appear on the head at a relatively young age.

Genetic Predisposition: The clear breed predisposition suggests a likely genetic component.

While no significant differences have been reported based on sex or neuter status, regular skin and abdominal examinations are important for cats in middle age and older.

Early Symptom Checklist by Type

Mast cell tumor symptoms vary significantly depending on where the tumor develops. Cutaneous (Skin) Symptoms

Small Lumps or Nodules: Firm or soft lumps appear on the head, neck, or body.

Recurring Itching: Your pet constantly scratches or licks around the lump.

Size Fluctuations: The lump may repeatedly grow and shrink.

Visceral (Spleen or Gastrointestinal Tract) Symptoms

Chronic Vomiting: Vomiting that persists for more than a month.

Weight Loss: Losing weight despite maintaining a normal appetite.

Loss of Appetite and Lethargy: Suddenly refusing food and showing signs of weakness.

Blood in Stool or Black Stool: These may occur with gastrointestinal mast cell tumors.

A lethargic cat lying down — symptoms of mast cell tumor

Seek Immediate Veterinary Care for These Symptoms

Seek veterinary care within 24 hours if you notice any of the following symptoms: • Sudden, repeated vomiting (more than three times a day) • Blood in the stool or black, tarry stools • Complete loss of appetite lasting more than 24 hours • A visibly distended abdomen • Extreme lethargy or persistent hiding behavior Excessive histamine release from mast cells can lead to gastric and duodenal ulcers and bleeding, resulting in symptoms such as loss of appetite, vomiting, anemia, and melena (black, tarry stools). You should also avoid strongly stimulating or pressing the tumor site.

How Are They Diagnosed? — Step-by-Step Testing

Diagnosing mast cell tumors is a step-by-step process.

Fine-needle aspiration (FNA): Cells are collected from the lump using a thin needle and examined under a microscope. This is a quick and simple first-line test for skin-type tumors.

Biopsy: Tissue is sampled for pathological examination to confirm the diagnosis.

Blood and urine tests: These assess the pet’s overall health and organ function.

Abdominal ultrasound: This checks for abnormalities in the spleen and internal organs.

CT scan: This is used to precisely determine the tumor’s extent and check for metastasis.

If there is suspicion of spread, systemic staging tests are performed to evaluate the full extent of metastasis.

Feline Abdominal Ultrasound Examination — Diagnosis of Mast Cell Tumor

Treatment Options — Approaches Vary by Type

Cutaneous form: Surgical excision is the primary treatment. Since most cases are well-differentiated benign tumors, surgery alone often leads to a cure, and chemotherapy is rarely necessary. If complete excision is difficult or incomplete, additional treatments such as radiation therapy may be considered.

Splenic form: Splenectomy is the cornerstone of treatment. Even if there is partial involvement of other organs, removing the spleen can still lead to relatively good survival rates and quality of life.

Intestinal form: Surgery and chemotherapy can be used together. The specific drugs and dosages are determined by the veterinarian based on the pet’s weight and overall health status.

Regardless of the type, consulting with a veterinary oncologist before starting treatment can help create a more detailed and tailored care plan.

Prognosis and Survival Time — Significant Differences by Type

Cutaneous form: This type carries the best prognosis. Cats in stages 1–3 rarely die from mast cell tumors, and many achieve long-term survival with surgery alone. However, recurrence can occur in some cases, and it has not yet been proven that the completeness of surgical excision predicts whether the tumor will recur.

Splenic form: After splenectomy, relatively good long-term survival and quality of life can be expected. The cat’s overall systemic condition before surgery has a significant impact on the prognosis.

Gastrointestinal form: Among the visceral forms, this type has a poorer prognosis, making early detection and prompt treatment decisions even more critical.

Regardless of the type, regular follow-up examinations every 3–6 months after treatment are essential to consistently monitor for recurrence.

Home Care Points You Can Manage

Proper home care after treatment can significantly impact your pet’s prognosis.

Monitor weight and appetite: Weigh your pet at the same time each week and keep a record of any changes in food intake.

Track vomiting episodes: Note the date, frequency, and appearance of vomit, as this information is invaluable during veterinary visits.

Regular skin checks: During grooming, gently feel over your pet’s entire body to detect any new lumps or bumps.

Minimize stress: Reduce environmental changes and provide ample hiding spaces.

Adhere to prescription diets: Strictly follow the dietary guidelines prescribed by your veterinarian.

A caregiver tenderly caring for their cat at home.

Siamese Cat Owners Need Extra Caution

Siamese cats have a higher predisposition to mast cell tumors, particularly atypical (histiocytic) cutaneous mast cell tumors that tend to appear on the head at a relatively young age. If you notice any new lumps or nodules on your cat’s skin, don’t dismiss them as simple skin issues; instead, have them evaluated with a fine-needle aspiration (FNA). Even if your cat shows no symptoms, we recommend regular health check-ups every six months.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Can feline mast cell tumors be transmitted to humans or other animals?

No, mast cell tumors are not contagious. They cannot spread to people or other pets.

How can I tell if a lump on my pet’s skin is a mast cell tumor?

It’s difficult to distinguish them with the naked eye. A fine-needle aspiration (FNA) test at an animal hospital can quickly identify the cell type. If you notice a lump, it’s best to have it checked right away.

What should I do if the condition recurs after surgery?

Depending on the location and extent of recurrence, we may recommend additional surgery, radiation therapy, or chemotherapy. Regular follow-up exams every three to six months after surgery help detect early recurrence.

Won’t my cat suffer too much from cancer treatment?

Depending on the chemotherapy drug, side effects such as diarrhea, vomiting, and loss of appetite may occur. Therefore, your veterinarian will carefully adjust the dosage based on your pet’s weight and overall health status. However, in cats with cutaneous (skin) tumors, surgery alone often leads to a cure, so chemotherapy is not always necessary. Please consult your veterinarian about any changes in your pet’s condition or concerns during treatment.

Is there a way to prevent mast cell tumors?

There is currently no definitive way to prevent this condition. The best approach is to increase the chances of early detection through regular check-ups every six months to a year, and to visit the clinic immediately if you notice any new lumps on your pet’s skin.

7 Factors Determining Prognosis and Life Expectancy in Dogs with Tumors, According to Veterinarians

7 Key Points of Canine Tumor Immunotherapy Selected by Veterinarians — From Principles to Selection Criteria

7 Criteria Veterinarians Recommend for Choosing Canine Tumor Biopsy and Fine-Needle Aspiration

If Your Cat Keeps Having Seizures — Warning Signs of Hypoparathyroidism and Hypocalcemia

When Your Cat Is Lethargic and Stumbling — Hypoglycemia Warning Signs and Emergency Response

Cat Suddenly Trembling and Having Seizures — Warning Signs of Hypocalcemia and Emergency Response

If Your Cat Is Eating a Lot but Losing Weight — Causes and Treatment Timing for Hyperthyroidism

Cats with Decreased Appetite but Weight Loss — Causes and Treatment Timing for Hyperthyroidism

Cat Drinking Water and Urinating Frequently — Causes and Management of Hyperglycemia

Cats Drinking Excessive Water — Causes of Hypercalcemia and When to Visit the Vet

References

[1] Withrow SJ, Vail DM, Page RL. Withrow and MacEwen's Small Animal Clinical Oncology, 5th Ed. Saunders Elsevier, 2013. Chapter: Mast Cell Tumors of the Cat.

[2] Litster AL, Sorenmo KU. Characterisation of the signalment, clinical and survival characteristics of 41 cats with mast cell neoplasia. J Feline Med Surg. 2006;8(3):177-83.

[3] Dank G et al. Treatment of feline visceral mast cell tumors with lomustine (CCNU). J Feline Med Surg. 2015;17(3):173-6.

[4] Blackwood L et al. European consensus document on mast cell tumours in dogs and cats. Vet Comp Oncol. 2012;10(3):e1-29.

[5] Gieger TL et al. Biologic behavior and prognostic factors for mast cell tumors of the cat. In Veterinary Oncology: A Short Textbook, 2018.