What are mast cells?
Mast cells are found all over the body. They are derived from bone marrow, and are found in all connective tissue, which is tissue that connects, supports or separates other tissues or organs.
They are found in skin (the largest connective tissue on a dog's body - or a human's) and these are also present in the intestines and respiratory tract.
Mast cells serve several purposes:
- Contain chemicals including histamine, heparin, and proteolytic enzymes. These chemicals are activated during an immune system response; such as if a dog is having an allergic reaction or in defense of parasitic attack
- Work to repair tissue
- Play a role in the formation of blood vessels
What are mast cell tumors?
A tumor is any type of abnormal growth.
When mast cell tumors (abnormal growth of a cluster of mast cells) develop on a dog, they can be benign (non-cancerous) or malignant (cancerous). In addition, and importantly, a benign mast cell tumor can spread (metastasize) and become malignant.
There are 3 grades:
Low potential for metastasis and considered presently benign. They can range in size from small to large. May or may not be removed. This depends on where they appear and if they appear to be growing.
Potential for metastasis and shows some characteristics of possibly turning malignant. These often extend below the skin and are intricately weaved into subcutaneous tissues, which is the inner most layer of the skin, containing blood vessels and nerves. May or may not be removed; more ahead.
High potential for metastasis. These are also deep into subcutaneous tissues and have the highest determination to metastasize. Are often removed; however that presents issues as well, more ahead.
The causes are unknown; however, both genetics and environmental factors are suspected.
Occurrence rate and stats
• Out of all skin tumors found on canines, 20% are mast cell tumors. The Boxer breed has more mast cell tumors that any other breed.
• The age that these appear is, on average, 8 years old. But, they can appear at a much younger age.
• They can spread to lymph nodes, and do in 76% of dogs.
• Occurrence or tumor-related death is 3.5% for the Boxer breed.
• A study by Kansas State University
shows that they most often occur on the abdomen or hind leg (40.4%), chest or foreleg (28.9%), genitals or anal region (17.5%) and head or neck (13.2%).
The vet will take a tissue sample of the tumor by either by Fine needle aspiration or a biopsy and bloodwork will be done.
Treatment for mast cell tumors
Keeping in mind that these tumors can be grade 1 through 3, some may be left but watched carefully, and some may be removed. Removing them presents several challenges:
- When a mast cell tumor is removed, it can trigger large quantities of the chemicals it holds (histamine, heparin, and others) into the body. And this can cause complications including a sometimes dangerous effect on heart rate and blood pressure.
- It is common for the removal site to refuse to heal, leading to open wounds.
- For the surgery to be successful, surrounding tissue must also be removed. It is very difficult to ascertain exactly where the tumor ends and healthy tissue begins. For this reason, a wide portion of healthy tissue is often removed.
There are other possible treatments as well, depending on how aggressive the mast cell tumors are. This includes radiation and chemotherapy.
This mainly depends on the grade of the mast cell tumor and where it is located. In regard to location, prognosis is best for those on the limbs. It is poor for those found on the genitals, muzzle, mouth, and nail bed area of the paws. It is very poor for those found in internal organs or in bone marrow.
In regard to the grade, for grades I and II that were fully
removed, the success rate of no recurrence within 3 years is 90 to 95%.