Immunohistochemical localization of the bone morphogenetic protein-6 in salivary pleomorphic adenomas

Salivary pleomorphic adenomas are often associated with chondroid tissue fo rmation. We have found that bone morphogenetic proteins (BMP), especially B MP-P, may play an important role in ectopic chondrogenesis in this tumor. B one morphogenetic protein-6 was reported to be related to the osteogenic me tastasis of prostatic carcinomas. The relationship between BMP-6 expression and chondroid tissue formation is investigated. Twenty-three pleomorphic a denomas were examined immunohistochemically. The overexpression of BMP-6 wa s observed in 10 pleomorphic adenomas of the major salivary glands (43.5%), and no evidence of BMP-B expression in any of the nine pleomorphic adenoma s of the palate. Bone morphogenetic protein-6 was immunolocalized in the la cuna cells of the chondroid tissue, in which type II collagen was localized . Bone morphogenetic protein-6 was expressed in inner ductal cells of the t ubulo-glandular structures in the pleomorphic adenomas. This finding indica tes that BMP-B may be associated with the differentiation of inner ductal c ells. Bone morphogenetic protein-6 was expressed weakly in neoplastic myoep ithelial cells in the myxoid areas, which may be related to the production of extracellular matrices. Bone morphogenetic protein-6 has a role in chond roid formation, and also tubulo-glandular differentiation in pleomorphic ad enomas. In conclusion, a large portion of pleomorphic adenomas of the saliv ary gland origin, but not of palate origin, was shown to overexpress BMP-6 protein.