IMMUNOREACTIVE METALLOTHIONEIN IN SALIVARY-GLAND NEOPLASMS

Metallothionein (MT), a low molecular weight intracellular protein pre sent in cytoplasm and nucleus, possesses a selective binding affinity for zinc, copper and other group II heavy metal ions which may have a potential role to bind, sequester or detoxify these metal ions and alt er the treatment response to chemotherapy or radiotherapy. The present study describes expression of MT in normal salivary glands and neopla stic salivary lesions using immunohistochemical method. Immunoreactive MT in normal salivary glands was observed in ductal cells where the i mmunostaining was most prominent in ductal basal cells of excretory an d striated ducts and intercalated duct cells. Expression of MT was als o observed in various salivary tumors; pleomorphic adenoma had immunor eactive MT in fibrillar and plasmacytoid neoplastic myoepithelial cell s and chondroid cells whereas Warthin's tumor, monomorphic adenoma and adenoid cystic carcinoma had non-luminal or basally located tumor cel ls intensely reactive. Acinic cell carcinoma cells were weakly reactiv e, however, papillary cystadenocarcinoma had a mixed population of cel ls with majority of the tumor cells moderately, and few cells strongly reactive, The profile of distribution of MT in salivary gland tumors was similar to that for S100 proteins suggesting their coexpression. T he result of the present study suggests that MT is expressed in normal salivary glands. In various salivary gland tumors, in spite of histop athological heterogeneity, differentiation, binding potential and sequ estration or detoxification of toxic metal ions by MT may confer a het erogeneous biological behavior. They also respond to the therapeutic m odality of radiation and chemotherapy.