Mast Cell Tumors

Any mass that’s pea-sized or larger should have a cytology performed on it.

At Two Rivers Vet Hospital in Fargo, ND, we often help pet owners navigate the unexpected discovery of a lump or bump on their dog or cat. One important cause of skin masses in pets is a mast cell tumor (MCT)—a common type of skin cancer that can behave in very different ways depending on the individual pet.

Mast cells are part of the immune system, normally involved in allergic responses and inflammation. But when they multiply abnormally, they can form tumors in the skin or under the skin’s surface. In dogs, mast cell tumors are the most common type of skin cancer, while in cats, they are less common but still significant.

MCTs can vary greatly in appearance. Some look like small, hairless bumps, while others may grow rapidly or change in size day to day. Some tumors may be itchy or inflamed due to the release of histamine and other chemicals. For this reason, we always recommend having any new or changing lump examined by a veterinarian.

Diagnosis is key. We usually begin with a fine needle aspirate (FNA)—a simple, minimally invasive test to examine the cells. If a mast cell tumor is confirmed, we may recommend surgical removal, followed by biopsy to grade the tumor and determine whether further treatment is needed.

While some MCTs are low-grade and cured with surgery alone, others are more aggressive and may require additional therapies such as radiation, chemotherapy, or immunotherapy. Early detection is critical to improving outcomes.

If you’ve noticed lump the size of a pea or larger on your pet, and it’s been present for at least a month, don’t wait. Schedule an exam with our compassionate team at Two Rivers Vet Hospital—your trusted veterinarian in Fargo, ND—to discuss options and next steps.