Freeze-fracture study of intercellular junctions in benign and malignant mesothelial cells in effusions and a comparison with those seen in pleural mesotheliomas (solid tumour).

This study involves an analysis by thin section and freeze-fracture techniques of the intercellular junctions of exfoliated benign and malignant mesothelial cells obtained from 4 cases, two benign and two malignant effusions. Pleural biopsies (solid tumours) of two further cases of confirmed epithelial malignant mesotheliomas were also studied to compare the organization, distribution and characteristics of the tight junctions, gap junctions and desmosomes observed between the three groups of cases. The results showed that both tight and gap junctions varied greatly in their organization in the exfoliated benign and malignant mesothelial cells. However they were often large and very well developed. In contrast, the tight and gap junctions in the solid tumours were considerably reduced both in their size and frequency, a feature which is well recognized in the literature as consistent with the neoplastic process. Our observation of florid tight and gap junctions in the exfoliated benign and malignant mesothelial cells, raises some important aspects of behaviour of neoplastic cells in effusion fluid. It is our opinion that cells in the fluid are exposed to microenvironmental influences which are quite distinct from those in a 'solid' tumour. We suggest that alteration in the binding sites of the extracellular matrix molecules, their influence on the cytoskeleton and the consequent effect on the development of tight and gap junctions are important factors which need further elucidation. The most significant feature of this study is however the demonstration of essential differences in the cell junctional characteristics between neoplastic mesothelial cells in body cavity fluids and those in tissues thus emphasizing the importance of environmental influences in the development of a neoplasm and its spread.