Mast Cell Tumors
What is it?
Mast cell tumors are the most common skin cancer in dogs. They can look like almost any lump, from a small raised bump to a swollen, red mass, and may change size from day to day. Boxers, Boston terriers, Labradors, and pugs are among breeds at higher risk.
What signs should I watch for?
Signs to watch for include A new or changing skin lump; A lump that swells, reddens, or itches; and vomiting or appetite loss in some cases.
How is it diagnosed and treated?
A needle sample can usually identify the tumor; a biopsy determines its grade. Surgical removal with a margin of normal tissue is the main treatment. Higher-grade tumors may need further staging, radiation, or chemotherapy.
Can it be prevented, and what's the outlook?
- Outlook depends heavily on grade and stage; many low-grade tumors are cured by surgery.
- Have every new lump checked.
Reviewed by the Adler Veterinary Hospital veterinary team, October 2026.
Dogs; Boxers, Boston terriers, Labradors, pugs at higher risk
Who's at risk:
New or changing skin lump that swells, reddens, or itches
Main signs:
Schedule a visit soon
Urgency:
When to call a vet right away
- A lump that suddenly swells, reddens or grows quickly
- Vomiting or loss of appetite
- Black, tarry stools
- Lethargy
- A rounded or swollen belly
Not sure whether it can wait? Call us anyway. Our team can help you decide.
Source:
Related conditions
Histiocytoma
Fatty Tumor (Lipoma)
Skin Cysts