Three dimensional visualization of the matrical fibrous structure of pleomorphic adenomas of the parotid glands was performed by the freeze-fracture, deep-etch replica method (D-E). Three types of fine architecture, two in the myxoid area and one in the chondroid area, which could not be observed by ordinary transmission electron microscopy (TEM), were revealed. In addition, granular connections between the tumor cell membrane and matrical fibers, probably cell surface proteins, were visualized.
In the myxoid area, one type of matrix which has a structure that cannot be identified on TEM, D-E demonstrated a uniform fine fibrous network consisting mainly of 7-10 nm diameter filaments and various architectures. These structual components were interlinked in a specific order and formed a basement membrane-like structure which contained the so-called‘hexagon-lattice structure’ reported by Sawada. Another type which appears as an irregular spotty structure and a few collagen-bundles on TEM, was revealed by D-E to be composed of a fine fibrous network and collagen-bundles. The collagen-bundles and the network were also interconnected to form a more complicated network.
In the chondroid area, the type of matrix appearing as a mottled amorphous area consisting of electron-dense and electron-lucent parts on TEM, was shown by D-E to be composed of mainly collagen-bundles and a less prominent fine fibrous network.
As for the cell surface, there were numerous granular structures which were seen to be anchored within the membrane and rigidly connected with 7-10 nm diameter fibrils. However, direct connections between the cell membrane and collagen-bundles were unremarkable. No tumor cell basement membrane was observed.
These findings indicate that, in constructing the tumor tissue and maintaining the tumor cells, the matrix could preserve suitable environment for these cells, and that the matrix and tumor cells may influence each other. To date, the matrix of this tumor has been regarded as a relatively uninteresting element. It was thought to lack any apparent structure and have little involvement in tumor biology. We, on the other hand, believe that this tumor matrix is an important component, and that furture investigation of this matrix will provide new insights into the study of pleomorphic adenoma.