In cattle, mast cell tumors have been reported in the skin, with and without metastases, and in various tissues including the heart, lung, spleen, mediastinum, peritoneum, and tongue. Cattle of all ages, including calves, are affected. In dogs, mast cell tumors are often graded based upon the degree of cellular atypia and infiltration. High grade tumors are more likely to metastasize, most commonly to the regional lymph nodes, spleen, liver, and bone marrow. Post-surgical recurrence of cutaneous mast cell tumors is common because they are poorly delineated and tend to infiltrate widely.
Cats develop cutaneous and visceral mast cell tumors.
These tumors appear to be separate diseases and not metastatic extensions of one or the other. Feline cutaneous mast cell tumors are less infiltrative than those in dogs and do not metastasize as frequently. Siamese cats are predisposed to a second histologic type of mast cell tumor that occurs in the cat. These tumors tend to be multiple, and the neoplastic mast cells resemble histiocytic cells and often do not display metachromatic granules when stained with Giemsa, toluidine blue, or Luna mast cell stains. Equine mast cell tumors are benign and frequently have more extensive mineralization, collagen degeneration, and vascular necrosis than those in other animals.