What is a mast cell tumour?

A mast cell tumour is one of the most common tumour types in dogs and cats. It typically arises in the skin or subcutaneous tissue and can vary widely in behaviour. Diagnosis requires veterinary examination and pathological testing.

How does a vet diagnose a mast cell tumour?

The vet will usually start with fine-needle aspiration (FNA) cytology for an initial assessment, followed by tissue biopsy (histopathology) and imaging if needed. The final diagnosis is determined by a pathology report.

Are mast cell tumours contagious?

No, mast cell tumours are not contagious. They result from abnormal proliferation of an individual animal's own cells and cannot be passed to other pets or people. If you have concerns about any skin condition, speak with your vet.

How often should follow-up check-ups happen after treatment?

Follow-up frequency depends on the tumour grade, stage, and treatment approach. Return visits are commonly scheduled every few weeks to months after treatment to monitor progress. Follow your vet's recommended schedule.

How much do the tests and treatment usually cost?

Costs vary by clinic and region — ask your vet for an estimate before proceeding.

Disease Guide

Mast Cell Tumours in Dogs & Cats: Symptoms, Diagnosis & Treatment [2025]

Mast cell tumours are one of the most common skin tumours in dogs and cats. Malignancy varies widely; wide surgical excision is the primary treatment, and pathological grading is essential for assessing prognosis.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

Pethealthmap Editorial Team

Sources: WSAVA, ACVIM, National Taiwan University Veterinary Teaching Hospital

When to See a Vet

Seek Emergency Care Immediately

•Repeated vomiting with inability to eat for an entire day
•Rapid and noticeable swelling of the face or lips
•Bleeding or ulcerated mass with heavy discharge

Schedule a Clinic Visit Soon (within 24–72 hours)

•Noticeably reduced alertness and decreased activity level
•Continuous and significant weight loss lasting more than two weeks
•Skin mass rapidly increasing in size or changing in shape

01What signs indicate something is wrong?

Mast cell tumours in dogs and cats commonly present as skin or subcutaneous lumps, and may be accompanied by systemic signs. Symptoms vary depending on the individual and tumour location.

Single or multiple lumps on the skin or just beneath the skin surface
Rapid change in lump size, shape, or colour over a short period
Lethargy or noticeably reduced activity levels
Decreased appetite or a sustained drop in food intake
Recurring vomiting or persistent diarrhoea
Ongoing weight loss or local skin ulceration and bleeding

Seek emergency care immediately if you notice the following symptoms:

⚠️ Lump rapidly enlarging or suddenly rupturing and bleeding
⚠️ Persistent vomiting or frequent diarrhoea
⚠️ Extreme lethargy, unresponsiveness, or obvious weakness

02How can I assess the situation at home? Key observation points and when to seek emergency care

Observing and documenting at home before the visit helps your vet assess disease progression and prioritise care.

Record your pet's energy level and activity changes daily
Note daily appetite and the actual amount eaten (portion size)
Count and log the frequency and timing of any vomiting or diarrhoea
Weigh your pet regularly and keep a record (photos or a log sheet)
Photograph or video any lumps or skin changes for comparison over time
Note when symptoms first appeared and any medications or treatments already given

03How will the vet diagnose this? Common diagnostic steps

Your vet will use a staged approach of physical examination, imaging, and pathology to assess tumour extent and any involvement of internal organs.

Full physical examination to assess lump location and overall body condition

Fine-needle aspiration (FNA) cytology as an initial diagnostic tool

Tissue biopsy (histopathology) to confirm tumour type and grade

Abdominal ultrasound or X-rays to check for internal spread

CT scan or advanced imaging to evaluate the extent of disease

Immunohistochemistry or PCR to assist with pathological subtyping

Referral to a specialist oncology centre for comprehensive evaluation is recommended

04What comes after diagnosis? Treatment, medications, and home care guide

Treatment and monitoring for mast cell tumours depend on the location, stage, and individual circumstances. Post-treatment follow-up and home care are equally important.

Surgical excision or local management as assessed by the vet
Additional medical therapy with blood monitoring as needed
Wound care and monitoring for signs of infection during and after treatment
Regular imaging or biopsy follow-up scheduled according to your vet's plan
Return visits to assess treatment response, side effects, and whether the plan needs adjustment
Contact your vet promptly if you notice any changes such as lump enlargement, ulceration, or new systemic signs

05What should I prepare before the vet visit? Key information to help your vet quickly identify the problem

Document when symptoms first appeared and how they have changed (including photos)

List the frequency of vomiting or diarrhoea and daily food intake records

Bring recent weight records or weigh-in photos for reference

Prepare a list of all current medications and supplements

Bring any previous pathology, cytology, or imaging reports if available

Use a secure carrier and bring your pet's familiar food to reduce stress

This content is for reference only and cannot replace a professional veterinary diagnosis. If your pet shows signs of illness, please seek veterinary care promptly.