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

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Abstract
Salivary pleomorphic adenomas are often associated with chondroid tissue formation. We have found that bone morphogenetic proteins (BMP), especially BMP‐2, may play an important role in ectopic chondrogenesis in this tumor. Bone morphogenetic protein‐6 was reported to be related to the osteogenic metastasis of prostatic carcinomas. The relationship between BMP‐6 expression and chondroid tissue formation is investigated. Twenty‐three pleomorphic adenomas were examined immunohistochemically. The overexpression of BMP‐6 was observed in 10 pleomorphic adenomas of the major salivary glands (43.5%), and no evidence of BMP‐6 expression in any of the nine pleomorphic adenomas of the palate. Bone morphogenetic protein‐6 was immunolocalized in the lacuna cells of the chondroid tissue, in which type II collagen was localized. Bone morphogenetic protein‐6 was expressed in inner ductal cells of the tubulo‐glandular structures in the pleomorphic adenomas. This finding indicates that BMP‐6 may be associated with the differentiation of inner ductal cells. Bone morphogenetic protein‐6 was expressed weakly in neoplastic myoepithelial cells in the myxoid areas, which may be related to the production of extracellular matrices. Bone morphogenetic protein‐6 has a role in chondroid formation, and also tubulo‐glandular differentiation in pleomorphic adenomas. In conclusion, a large portion of pleomorphic adenomas of the salivary gland origin, but not of palate origin, was shown to overexpress BMP‐6 protein.