NCIt definition : A localized tumor composed of sheets of mast cells without atypia. It includes the
cutaneous mastocytoma which involves the dermis and subcutaneous tissue, and the extracutaneous
mastocytoma. Most cases of extracutaneous mastocytoma have been reported in the lung.;
Alternative definition : NCI-GLOSS: A growth or lump of mast cells (a type of white blood cell). Mast cell
tumors can involve the skin, subcutaneous tissue, and muscle tissue.;