Mast Cell Tumor
--mast cell tumors are a common malignant tumor of the skin in older dogs and cats
--20 to 25 percent of skin tumors in dogs are mast cell tumors, similar number in cats
--breeds commonly affected: boxer, bulldog, basset hound, weimaraner, Boston terrier, golden retriever, labrador retriever, beagle, German shorthaired pointer, Scottish terrier, PUG, Rhodesian ridgeback
--aka: mastocytoma
--accumulation or nodule of mast cells
--mast cells originate from the bone marrow and are normally found throughout the connective tissue
--a normal component of the immune system, releases histamine associated with allergic reactions
--also respond to tissue trauma
--mast cell granules contain histamine, heparin, platelet-activating factor, and other substances
--disseminated mastocytosis is rarely seen in young dogs and cats
--known as 'the great pretenders' due to varying presentation
--S/Sx: most mast cell tumors are small, raised lumps on the skin, may be hairless, ulcerated, or itchy, usually solitary but in about 6 percent of cases there are multiple tumors (esp in Boxers and Pugs)
--presentation: wart-like nodule to a soft subcutaneous lump (similar on palpation to a benign lipoma) to an ulcerated skin mass
--Dx: lumps should be checked by fine needle aspiration: palpation or visual inspection not adequate
--manipulation of the tumor may result in redness and swelling from release of mast cell granules, also known as Darier's sign, and prolonged local hemorrhag
--rare: highly malignant tumor, signs: loss of appetite, vomiting, diarrhea, and anemia--> usu indicates mastocytosis, which is the spread of mast cells throughout the body
--release of a large amount of histamine at one time can result in ulceration of the stomach and duodenum (up to 25 percent of cases), or disseminated intravascular coagulation
--usu destinations for metastasis: liver, spleen, lymph nodes and bone marrow