Mast cell tumors are one of the most common tumors I see on the skin and subcutaneous tissues of dogs although they can occur anywhere. Mast cells are part of the immune system and are found all over the body. Mast cell tumors occur when the inhibitory signal is lost and a mast cell replicates without any control. These tumors grow fast and can be difficult to remove. Malignant cells creep into the surrounding tissues from a tumor making it difficult to get clean margins.
Pictured below is a 9 year old spayed female Australian shepherd mix named Molly. She was always a healthy girl until 4 months ago when she started having respiratory problems. X-rays of her abdomen and chest revealed large tumors. She needed furosemide therapy to treat the fluid that accumulated in her lungs and chest from the cancer. Tumors also appear on her skin including a small pink mass on her lower right eyelid. The tumor grew quickly into a large ulcerated mass pictured below. Microscopic analysis of her lump revealed a mast cell tumor.
Since surgical removal is not an option for Molly, her family has decided to treat her with masitinib mesylate (Kinavet-CA1) made by AB Science, Chatham, New Jersey. Masitinib is approved for the treatment of nonresectable grade II and III cutaneous mast cell tumors in dogs. It is a tyrosine kinase inhibitor that targets the c-Kit receptor. In dogs who have the c-Kit mutation, the results have been remarkable.
Molly started her treatment on Monday. The tablets are given once a day with food. So far, she is tolerating the medicine well. Please keep your fingers crossed for Molly.
-AB SCIENCE, Kinavet-CA1: Canine Mast Cell Tumor Targeted Therapy, Promotional Materials. www.kinavet.com.
-Shell, Linda. ‘Mast Cell Tumor’ Associate, VIN.com, last updated 06/06/2011.