Expression of bone matrix proteins, osteonectin and osteopontin, in salivary pleomorphic adenomas

Osteonectin (OSN) is a glycoprotein involved in the early steps of the mine ralization of skeletal tissue, while osteopontin (OPN) is a protein involve d in normal and pathological calcifications. OSN and OPN are non-collageneo us bone matrix proteins expressed by some epithelial tumor cells in excepti onal cases. We immunohistochemically investigated the presence and the dist ribution of OSN and OPN in 43 pleomorphic adenomas to elucidate the product ion of their molecules by modified myoepithelial cells. In normal salivary glands, OSN was immunolocalized in the striated ducts, while OPN was not ex pressed. In pleomorphic adenomas, the inner layer of tubulo-glandular struc tures and modified myoepithelial cells in the myxoid areas showed moderate positivity for OSN (83.7%). OSN was expressed in all of the lacuna cells in the chondroid areas. OPN was strongly expressed in the stroma of the myxoi d and hyaline areas of the pleomorphic adenomas (65.1%), but there was no e xpression of OPN in the chondroid area. All cases of pleomorphic adenomas e xpressed type IV collagen. These findings suggested that OSN was related to the production of the type IV collagen by modified myoepithelial cells, wh ereas OPN was involved in the stromal formation of myxoid or hyaline tissue s in pleomorphic adenomas, In summary, pleomorphic adenomas expressed the b one matrix proteins OSN and OPN.