Mast Cell Tumors in Dogs: Skin Cancer Guide
Mast cell tumors are the most common skin cancer in dogs. Accurate grading guides treatment and prognosis.
Mast cell tumors (MCT) are malignant skin tumors arising from mast cells — immune cells involved in allergic reactions. They're the most common skin cancer in dogs and have highly variable behavior, ranging from benign to highly aggressive.
Key Points
- Mast cell tumors account for 20% of all canine skin tumors
- Breeds at higher risk include Boxers, Bulldogs, Boston Terriers, and Pugs
- Tumors can look like anything — small bumps, large masses, or ulcerated lesions
- Tumor grade (1-3) predicts behavior — grade 3 is aggressive and prone to spread
- Surgical removal with wide margins is the treatment of choice
- High-grade tumors may need chemotherapy or radiation after surgery
Understanding Mast Cell Tumors
Mast cells contain granules of histamine and other chemicals. When a tumor is manipulated, these granules release, causing swelling, redness, and sometimes systemic effects. Tumors can change size and appearance. They can occur anywhere on the body but are most common on the trunk, limbs, and perineum. The skin around the tumor may look normal, inflamed, or ulcerated.
Diagnosis and Grading
Fine needle aspiration often provides a diagnosis — mast cells are easily identified. Biopsy with grading is essential. Grade I (low-grade): well-differentiated, slow-growing. Grade II (intermediate): moderate behavior. Grade III (high-grade): poorly differentiated, aggressive, high recurrence and metastasis rates. The Patnaik grading system is commonly used. Ki-67 and c-Kit staining help assess aggressiveness.
Treatment
Surgical excision with wide margins (2-3 cm lateral, one fascial plane deep) is the primary treatment for grades 1 and 2. Grade 3 tumors need aggressive surgery plus chemotherapy (vinblastine, prednisone) and sometimes radiation. Lomustine (CCNU) and other drugs are used for recurrent or metastatic disease. Tyrosine kinase inhibitors (toceranib, masitinib) target c-Kit mutations. Palliative care includes antihistamines and H2 blockers to manage histamine release effects.
When to See a Vet Immediately
- Your dog has a new skin lump that changes size
- There's redness or swelling around an existing lump
- A previously removed lump has regrown
- The lump is rapidly growing or ulcerated
- Your dog is a breed predisposed to mast cell tumors
How RVC Can Help
This article is for educational purposes only and does not replace professional veterinary advice. If your pet is showing any symptoms, please contact Royal Veterinary Center immediately at +853 6677 6611.