Mast Cell Tumor
Mast cell tumors (MCTs) are the most common skin tumors in dogs, arising from mast cells (immune cells involved in allergic and inflammatory responses). They are highly variable in behavior - from benign to highly malignant. MCTs can release histamine and other vasoactive substances causing systemic effects. Grading (Patnaik I-III or Kiupel low/high) determines prognosis.
Symptoms & Signs
- Skin mass (variable appearance - can mimic any tumor)
- Rapid size changes (degranulation)
- Redness and swelling around tumor
- GI ulceration (from histamine release)
- Bruising
- Poor wound healing
- Systemic signs if metastatic
Causes & Risk Factors
Unknown definitive cause. Genetic predisposition in certain breeds (Boxer, Boston Terrier, Labrador, Golden Retriever, Pug). KIT gene mutations (c-kit) identified in many canine MCTs, driving proliferation. Chronic inflammation may play a role.
Diagnosis
Fine needle aspirate with cytology (characteristic purple granules with Romanowsky stains). Histological grading of excised tumors. c-kit mutation testing for targeted therapy eligibility. Staging: regional lymph node aspirate, abdominal ultrasound, buffy coat examination.
Treatment
Surgical excision with wide margins (2-3cm lateral, one fascial plane deep). Radiation for incomplete excision. Chemotherapy (vinblastine/prednisolone) for high-grade or metastatic disease. Tyrosine kinase inhibitors (toceranib, masitinib) for c-kit mutated tumors. Antihistamines perioperatively.
Prevention
No proven prevention. Early detection through regular skin checks. Prompt investigation of any new skin mass. Genetic awareness in predisposed breeds.
Prognosis
Low-grade (Kiupel): excellent with complete excision (>90% cure). High-grade: guarded (median survival 4-6 months with treatment). Location matters: oral, preputial, and subungual carry worse prognosis. c-kit positive tumors respond to targeted therapy.