Mast Cell Tumours
The most common skin tumour in dogs — behaviour ranges from benign to highly aggressive depending on grade.
What is Mast Cell Tumours?
Mast cell tumours (MCTs) are the great imitators of the skin — they can look like a wart, a lipoma, or a firm nodule. They release histamine and other inflammatory chemicals, so they may fluctuate in size, become red, or cause GI upset. Grade (from biopsy) is the single most important prognostic factor.
Common signs and symptoms
Signs vary between dogs and can be subtle at first. Watch for the following, especially if several appear together or persist for more than a few days:
- Firm or soft skin lump that may wax and wane
- Redness or itchiness around the lump
- GI upset (vomiting, dark stools) with higher-grade tumours
- Sudden swelling if the lump is bumped ('Darier's sign')
Risk factors
Certain dogs are more predisposed. Understanding risk helps you screen earlier and act sooner.
- Boxer, Bulldog, Pug, Boston Terrier, Golden Retriever, Labrador
- Middle-aged to senior dogs
When to see a vet
Use this as general triage guidance, not a substitute for veterinary advice.
- Book a routine appointment if: any new skin lump — needle aspirate is quick, inexpensive, and diagnostic for MCT.
- Seek urgent care if: rapidly enlarging lump with vomiting or dark stools.
Diagnosis and management
Fine-needle aspirate confirms diagnosis; wide surgical excision with clean margins is standard. Grade (Patnaik or Kiupel), mitotic index, and c-KIT mutation status guide whether radiation or targeted therapy (toceranib) is added. Most low-grade MCTs are cured with surgery alone.