Prevalence
The most common skin tumor in dogs (~16–21% of all canine skin tumors). Boxers, Bulldogs, Boston Terriers, Pugs, and Labradors over-represented.
Who gets it
Median age 8 years. Boxers can develop them as young as 2. Brachycephalic breeds especially.
Symptoms to watch for
- A skin lump — can change in size from day to day (Darier's sign)
- Sometimes ulcerated or itchy
- Vomiting or GI ulcers if the tumor releases histamine
- Lymph node enlargement if metastatic
How it's diagnosed
- FNA — usually diagnostic; mast cells have distinctive granules
- Excisional biopsy with histology + Patnaik or Kiupel grading
- Mitotic index — single best prognostic factor
- c-KIT (KIT) mutation testing — tumors with internal tandem duplications respond to toceranib (Palladia)
- Lymph node aspirate (regional) and abdominal ultrasound for staging in high-grade cases
Prognosis ranges
Low-grade with clean margins: median survival >2 years, often curative. High-grade: median 4–18 months even with adjuvant chemo. Kiupel high-grade is the worst signal.
Treatment landscape
Recurrent mutations in this cancer
Frequencies from canine clinico-genomic cohorts. SciRouter Oncology auto-checks every mutation in your dog's report against the OncoKB-aligned database for matched targeted therapies.
Questions to ask your vet
- What's the Kiupel and Patnaik grade?
- What's the mitotic index?
- Did we test for c-KIT mutation?
- Were the margins clean? How clean?
- Should we biopsy the local lymph node?
- Do we need a re-excision or radiation?
Quality-of-life notes
MCTs can release histamine acutely (Darier's sign) — the lump may swell and itch. Pre-medication with diphenhydramine and famotidine before any manipulation is standard.