Mast Cell Tumours
Mast cell tumors are the most common type of skin tumor found in dogs and the second most common in cats. They are most often noticed in middle aged patients, but can occur in any age. They are the most prevalent in Boxers and Boston terriers; these two breeds actually make up 50% of all dog cases. They are still found in many other breeds as well, though.
Signs of mast cell tumors will relate to the grade and progression of the disease. Some animals will present with small, freely movable tumors in the skin or subcutaneous tissues with minimal surrounding inflammation. Others will have large, ulcerated, hairless tumors that are often associated with a more aggressive tumor. Symptoms such as vomiting, loss of appetite, and digested blood present in the stool (making the stool look very dark black) are also possible. The grade and prognosis related to the tumor cannot be determined until it is removed and analyzed in a histopathology lab.
These tumors can vary in size from day to day depending on the degree of inflammation in the cells. Your veterinarian can accurately diagnose a mast cell tumor with a needle aspirate of the tumor in almost all cases. Upon examination of the cells, they will show characteristic dark blue to purple intracellular granules. The grade of the tumor can be determined after a surgical biopsy and lab analysis.
Metastasis (the spread of tumor cells) occurs first at the local lymph nodes and then potentially to the bone marrow and visceral organs such as the spleen, liver, lungs, and other regions of the skin. It may be recommended to have needle aspirates of the lymph nodes or abdominal organs to look for metastasis at the time of diagnosis. Ultrasounds may be used to evaluate the size, shape and texture of tumors, as well as abdominal organs. Chest x-rays may also be recommended to rule out cancers or diseases that may affect your pet’s long-term prognosis prior to surgical recommendations.
The preferred treatment for mast cell tumors is surgical removal. Wide surgical margins will be necessary because these particular tumors are known to invade surrounding tissues, and it is important to ensure the removal of ALL cancerous cells. Prior to surgery, your vet may recommend the use of steroids, anti-histamines, and histamine blockers to help reduce the inflammation and associated side effects of the tumors. Post-surgical radiation and chemotherapy are warranted on a case-by-case basis.
Once the tumor is removed and analyzed using histopathology, the grade of the tumor will be determined. Your vet will then be able to give a more accurate prognosis for the pet. Long-term survival time and necessary follow-up treatment options may then be discussed. Additional prognostic factors include breed, clinical presentation, tumor location, and surgical margins.
The sooner you take your pet to the vet upon noticing any of the above mentioned signs and symptoms, the better. These tumors spread quickly so time is of the essence! Always be proactive about your pet’s health and yearly veterinary check-ups!