IDENTIFICATION OF METALLOTHIONEIN-POSITIVE AND PARATHYROID HORMONE-RELATED PEPTIDE (PTHRP)-POSITIVE CELLS IN SALIVARY-GLAND TUMORS

Ductal basal cells and myoepithelial cells (MEC) of normal salivary gl and share metallothionein (MT)-positivity, while PTHrP positivity is r estricted to ductal basal cells. We studied 21 benign and 4 malignant tumours in which MEC are thought to play a role using immuno-histochem ical methods for detecting the presence of MT and PTHrP positive cells . In benign tumours, a shared positivity for MT and PTHrP is found in the inner layer of tubulo-ductal and trabecular structures, in part of the cells in the myxoid and chondroid matrices of pleomorphic adenoma , and in the basal epithelial lining of Warthin's tumours. In myoepith elioma almost all tumour cells demonstrate MT reactivity and a restric ted positivity for PTHrP. MT-positive cells in oncocytoma were demonst rated in the periphery of some oncocytic islets, while PTHrP positivit y was restricted to a few oncocytic cells. In malignant tumours, posit ivity for MT is found in the periphery of epithelial clusters of mucoe pidermoid carcinomas, while PTHrP-positive cells are seen in cyst-like structures and scattered cells in solid arrangements of squamous cell s. Although the biologic significance of the presence of MT in neoplas tic cells is not yet clearly understood, MT may be necessary for the g rowth and differentiation in actively growing cells. the variability o f MT expression in salivary gland tumours could be a reflection of the morphological heterogeneity and correlate with the degree of differen tiation and maturation of the tumour cells. the observations suggest t hat MT may be considered an oncodevelopmental product.