Plasmacytomas of the oral cavity are less common than those involving the upper respiratory tract. They must be distinguished from plasma cell granulomas which are reactive lesions that may found in the same location. The plasma cell granulomas have mature plasma cells admixed with other inflammatory cells and show background fibrosis. With immunohistochemical stains for light chains, they show a polyclonal staining pattern. In contrast, solitary plasmacytomas of the upper respiratory tract are composed of neoplastic plasma cells with varying degrees of maturation. They show strong cytoplasmic staining for light chains with kappa or lambda restriction. The heavy chains are usually IgA type (in contrast to the predominance of IgG heavy chains in solitary plasmacytoma of bone). About 20% of patients show low levels of IgA monoclonal component in their serum or urine.