Dogs can also have tumors and one of the common types is the Mast Cell Tumors in dogs. Also known as mast cell sarcoma, histiocytic mastocytoma and mastocystosis, mast cell tumors in dogs are generally considered malignant or potentially malignant mass growths. It affects any breed of dogs and of any age, but are more common in 8 to 10 years old. About twenty percent of all skin tumors in dogs are attributed to mast cell tumors.
By Dr. Gary Thompson
Mast cell tumors (MCTs) are the most common tumor found in the skin and surrounding connective tissue in dogs, accounting for about one in five cutaneous tumors.
They arise from mast cells that are normally found near the surface of the skin, lungs and intestines. Their normal job is to protect against parasitic infections and to help promote the formation of new blood vessels during tissue repair. These cells contain histamine granules which are released during allergic reactions and are the source of the swollen, red bump you might get from a bee sting. As with any cancer, the growths stem from a failure of the body to regulate the growth and life cycle of these cells and they multiply unchecked.
The most dangerous part of MCTs is their ability to mimic many other skin growths. They can be hard, soft, big or small and some will even look like more common benign skin tumors. Some of these skin tumors grow quickly while others may not change over time with the majority being solitary growths. Occasionally MCTs can be found in the spleen or digestive system and the only symptom may be related to its impact on appetite. Some breeds like Boxers are more prone to develop MCTs, but it can affect any breed as they age.
Diagnosis is normally made through a simple test where cells are collected from the tumor called a fine needle aspirate (FNA).
Often your veterinarian can make the diagnosis with an FNA since it has a very characteristic microscopic appearance. Once a MCT is diagnosed some additional tests may be required to determine whether the tumor has metastasized or spread to other parts of the body.
Surgical removal of these tumors is complicated by the fact they have a more aggressive microscopic behavior which requires removing at least an inch of normal tissue in three dimensions around the tumor to ensure complete excision. About 40 percent of MCT are found on the legs which can complicate removal since there may not be enough normal tissue around the tumor to allow for closure of the area, so early diagnosis of these growths is critical.
To grade these tumors and confirm that it has been completely removed, your veterinarian will need to send the tumor to a veterinary pathologist after surgery. MCTs are graded from 1 to 3 depending on how aggressive they appear microscopically.
Ninety-five percent are grade I and 2 with complete and aggressive surgical removal being curative.
For grade 3 tumors or those that can’t be completely surgically removed, additional therapies like radiation, drugs or intra-tumor injections may be employed to either shrink the tumor or prevent spread to distal sites. In all these cases early diagnosis is critical for a good outcome so if you notice any new growths on your dog, regardless of what they may feel or look like, have your veterinarian evaluate them.
