Introduction

Mast cell tumors (MCTs) vary greatly in appearance and can occur in many different places on a dog’s body. Unfortunately, it is difficult if not impossible to determine whether a mast cell tumor is malignant or benign based upon appearance alone.

Symptoms of Mast Cell Tumors

A mast cell tumor usually shows up as an isolated lump or mass, although they can appear in clusters or in multiple areas of the skin. Most affected dogs show no symptoms of irritation or illness. Owners of dogs with mast cell tumors may notice one or more of the following:

• Lumps or bumps on or under the skin of the torso (trunk), underbelly (abdominal area) and hind legs, and around the anus and genital area
• Lumps or bumps anywhere on or under the skin
• Raised circular masses on or under the dog’s skin that feel soft on the outside but solid on the inside
• Skin mass that is multi-nodular (like cauliflower, with several bumps in a cluster)
• Skin mass that is reddish
• Skin mass that is hairless
• Skin mass that is itchy (pruritic)
• Skin mass that is ulcerated (like an open, weeping wound)
• Skin mass that appears completely normal other than that it is a lump on or under the skin
• Skin lump that looks the same for months or years, then suddenly changes in size or appearance
• Skin lump that shows up suddenly and enlarges rapidly
• Skin lump that fluctuates in size
• Signs of gastric irritation – vomiting, diarrhea, weight loss, bloody stool

Many of these signs can be associated with a number of conditions other than mast cell neoplasia. Again, the key point for owners to remember is that any bump or lump on a dog may be abnormal, may be cancerous and should be examined by a veterinarian.

Dogs at Increased Risk

Dogs of either gender and of any age can develop mast cell tumors. Older dogs, with a mean age of 8 to 9 years, are most commonly affected, although very young dogs have been diagnosed with this form of cancer. While dogs of any breed or mixed breed can be affected, certain breeds do seem more prone to developing MCTs, including brachycephalic breeds such as English Bulldogs, Boston Terriers, Pugs and Boxers, among others. The reason for this association is not clear. Other predisposed breeds are the Golden Retriever, Labrador Retriever, Shar-Pei, Staffordshire Bull Terrier, Jack Russell Terrier and Rhodesian Ridgeback. Bernese Mountain Dogs reportedly have a genetic predisposition to developing mast cell tumors.