Is This Lump Normal? Understanding Mast Cell Tumors in Dogs

How do you know if their lumps are concerning? photo: AdobeStock

About 10 years ago, my beloved dog Bogie developed some weird, pink, fleshy growths. At the time, he also seemed a little off and was vomiting. I was beginning my career as a registered veterinary technician, and I had learned to have any strange or new lumps checked out so I wasted no time setting up a vet appointment for him. 

The veterinarian examined the lumps and advised giving Bogie an injection of Benadryl. This was so she could perform a fine needle aspirate, which involves taking a small needle and inserting it into the lump to gather some cells (thankfully, this is a minimally invasive procedure, which can usually be done with your animal awake). The veterinarian then examined Bogie’s cells under a microscope. After a wait that seemed like forever, she returned and told me that he indeed had cancer - mast cell cancer to be exact. I was devastated, but Bogie’s doctor consoled me with information about the disease. This is what I want to share with you. 

Mast cell tumors are a cancerous group of mast cells and account for between 15%-20% of skin cancers. Mast cells are present in the skin and usually fight inflammation and allergic reactions by producing histamines. These mast cells, however, can congregate and form a tumor. The disease comes in different levels of severity, with Stage III being the most malignant or aggressive. The reason my veterinarian administered a Benadryl injection to Bogie first was that any time this tumor is disturbed, such as for a needle aspirate, it can release toxic granules that spread the cancerous process throughout the body. Benadryl is an antihistamine that will suppress this explosive process.

Once Bogie was diagnosed with mast cell tumors, the staging process began. This involved chest radiographs, bloodwork, and an abdominal ultrasound to see if the tumor had metastasized (spread) to anywhere else in the body, like his lungs or abdomen. In our case, Bogie’s mast cell disease seemed to be localized to his masses so my veterinarian arranged to have a veterinary surgeon come in to remove them. The tumors were in a very awkward spot (in his armpit and chest area), but the surgeon was able to remove them all with clear margins. This meant there was no cancer detectable in the outer areas of the tissues submitted to the lab. The tumors were also “low grade” which means a low level of malignancy. Bogie was cancer free! I was happy to have the mast cell tumors removed, but I knew eventually they’d come back, because that’s what they do.

Fortunately, there are many treatment options for mast cell tumors in dogs. Surgery is often recommended to remove the mast cell tumor. Radiation and chemotherapy are also available if indicated for your pet’s specific tumor. Additionally, there is a new method of removing these tumors called Stelfonta. In very simplified terms, it’s a drug injected into the tumor that will cause it to die off or necrose. This method is not without risk, though, so a thorough discussion should be had with your veterinarian if you’re considering it.

Mast cell disease is a disease of the skin and of the intestinal tract. Even if a staging diagnostic test comes back clear, one must realize that it’s impossible to truly remove it all. This is where diligence comes into play. Any new, odd, growing lumps, or any lumps that change in size should be checked as soon as possible by a veterinarian. 

My Bogie has had mast cell tumors removed four times now, over the past 14 years, and thankfully, they’ve all been low grade. I attribute this to my fastidiousness in always having new lumps checked out and removed if warranted. 

The bottom line on mast cell tumors? Keep your pup safe, and make sure you check those lumps!

This article is courtesy of SAGE Compassion for Animals.