2012 年 10 巻 4 号 p. 384-399
Pleomorphic adenomas are the most commonly occurring salivary gland tumors, which are histopathologically characterized by both the presence of epithelial cell proliferation and the formation of myxomatous or cartilage-like tissue. Given their variability, to date, there have been numerous morphological and immunohistochemical studies of the tumors, but most have focused on the major salivary gland tumors and minor salivary gland tumors have yet to be sufficiently investigated. The present study is a comparative histopathological and immunohistochemical study conducted with the aim of focus on the formation of cartilage-like tissue in pleomorphic adenomas occurring in the major and minor salivary glands. Histopathologically, the tumor parenchyma findings consisted of double-layered tubular (inner cells and outer cells), sheet-like, and cord-like proliferation of epithelial cells in all pleomorphic adenomas of the major salivary glands (11 cases) and minor salivary glands (50 cases). The outer cells of the tubular proliferation were dissociated and myxomatous or cartilage-like tissue interposed with matrix was observed. All cases (100%) of the major salivary gland tumors showed hyaline cartilage-like tissue formation that showed metachromasia on Tb staining at pH 7.0, pH 4.1 and pH 2.5. On the other hand, in the minor salivary gland tumors, chondrogenesis was present in 4 of 50 cases (8%), which was predominantly in the form of fibrocartilage-like tissue that presented metachromasia with Tb staining at pH 7.0 and pH 4.1. Immunohistochemical investigations revealed keratin-positive cells in both the inner cells and outer tumor cells in the area of double-layered tubular poliferation. In addition, vimentin- and S-100 protein-positive findings were observed in the outer cells and dissociated cells. The cartilage-like matrix in the major salivary gland tumors was remarkably positive for type II collagen, while the cartilage-like matrix in the minor salivary gland tumors was primarily positive for type I collagen. Markedly positive findings were observed in the hyaline cartilage-like tissue of the major salivary gland tumors for bone morphogenetic protein (BMP)-2, BMP-4 and BMP-6, fibroblast growth factor-2 and chondromodulin-I, which were associated with chondrogenesis. The results suggest that cartilage-like tissue forms more readily in the major salivary gland tumors than in the minor salivary gland tumors. Neoplastic myoepithelial cells are involved in the formation of cartilage-like tissue, and it can be inferred that due to the quantity of cartilage-inducing factors, the formation of cartilage-like tissue is more typical in the major salivary gland tumors than in the minor salivary gland tumors.
