Mast Cell Tumors in Dogs: Signs, Diagnosis, and Surgery

Mast cell tumors are the most common malignant skin tumor in dogs, and one of the trickiest to spot, because they can look like something harmless. That is exactly why any new or changing lump is worth having checked. At Apex Veterinary Surgery, our board-certified (DACVS) surgeons remove mast cell tumors and other masses for pets across Nashville, Memphis, and the surrounding areas. When one is caught and removed completely the first time, most dogs do very well.

Understanding Mast Cell Tumors

Mast cells are normal immune cells in the skin that release histamine, the same chemical behind an allergic reaction. A mast cell tumor is an abnormal growth of these cells. Because they’re full of histamine, these tumors can swell, redden, or shrink, and handling one can actually make a dog feel unwell, so don’t keep touching a suspicious lump. Most appear on or just under the skin and can show up anywhere on the body. They range from slow-growing and low-risk to aggressive, and the only way to know which one you’re dealing with is testing. A mast cell tumor can look identical to a harmless fatty lump, which is why appearance alone is never enough to rule it out.

How Mast Cell Tumors Are Diagnosed

Mast cell tumors are a form of cancer, but the outlook varies widely by grade, and the good news is they’re usually straightforward to identify. A veterinarian can take a small needle sample (a fine needle aspirate) and look at the cells under a microscope, often confirming a mast cell tumor quickly. After surgical removal, the tissue goes to a pathologist for a grade, which tells you how the tumor is likely to behave and whether further treatment is needed.

Why Complete Surgical Removal Matters

With mast cell tumors, the first surgery is the one that counts. These tumors send microscopic fingers of cells into the surrounding tissue, well beyond what you can see or feel, so removing them means taking a margin of healthy tissue all the way around and underneath the lump. Remove too little, and cells are left behind and the tumor returns, usually harder to treat. A board-certified surgeon plans that margin based on the tumor’s size and location, and can close the site even when a wide removal is needed somewhere tricky like a leg or the face.

When to See a Board-Certified Surgeon

Many small, low-grade mast cell tumors are removed by a primary veterinarian. Referral to a board-certified veterinary surgeon (DACVS) makes sense when the tumor is large, in a location with little spare skin, has come back, or sits somewhere hard to close completely. Getting the margins right the first time gives your dog the best chance at a cure and avoids repeat procedures.

Frequently Asked Questions

Are mast cell tumors always cancerous?

Yes, they are a type of cancer, but behavior ranges from low-grade tumors cured with complete surgery to higher-grade tumors that need more. The grade from pathology tells you which you’re dealing with.

Can a mast cell tumor be cured?

Often, yes. A low- to intermediate-grade tumor removed completely with clean margins is frequently cured by surgery alone. Higher-grade tumors may need additional treatment.

Should I have the lump removed even if it’s small?

A small mast cell tumor is easier to remove completely than a large one, so earlier is better. Have any new or changing lump checked rather than watched.

How is a mast cell tumor diagnosed?

With a fine needle aspirate: a vet draws a few cells with a small needle and examines them under a microscope, which often identifies a mast cell tumor quickly. Pathology after removal confirms the grade.

Does my dog need a referral?

We are a referral-based surgical practice. Your primary veterinarian can refer you, or you can contact us directly.

Schedule a Consultation

If your dog has a lump identified as a mast cell tumor, or one your veterinarian wants a specialist to remove, our board-certified surgeons can help.