[Immunohistochemical study of basement membrane in pleomorphic adenomas of the parotid gland: comparison between primary treated tumor and recurrent tumor].

We immunohistochemically investigated the distributions of components of the basement membrane (BM) (type IV collagen and laminin) and alpha smooth muscle actin in twelve primary pleomorphic adenomas of the parotid gland, as compared with six recurrent benign pleomorphic tumors (recurrent type). There were no differences between the two types of the tumor in the distributions of the BM components and actin, whereas the recurrent type of tumor have numerous myxochondroid areas histologically. The localization of type IV collagen in the tumor tissue was almost the same as that of laminin. Actin was identified in the occasional myoepithelial cell. In the tumor tissues, the components of BM were most densely localized in the areas surrounding solid clusters of epithelial cells, outer cells of glandular structures and occasional cells in the myxoid area, but the stroma of the myxochondroid areas did not take up stain. BM was densely defined between the tumor capsule and epithelial cells, but the tumor capsule was not bordered by myxochondroid areas with BM. These results suggest that loss of BM between the capsule and myxochondroid areas may be one of the causes of postoperative recurrence of pleomorphic adenomas.