Perivascular mast cells in advanced gastric adenocarcinomas: an electron microscopic study.

Mast cells are frequently found in close proximity to blood vessels and have been implicated in tumour angiogenesis. The aim of the present ultrastructural study was to characterize, in detail, the mutual association between mast cells and microvasculature in 9 cases of advanced gastric carcinoma. Perivascular mast cells were ultrastructurally identified as T mast cells and exhibited piecemeal degranulation, indicative of a slow release of granule-stored contents. In two cases they were adjacent to endothelial cells showing vesiculo-vacuolar organelles, a newly-defined endothelial cell permeability structure. Collagen fibres and dispersed fibrous long-spacing collagen were found near T mast cells in one case, suggesting their role in perivascular collagen degradation and/or turnover. Mast cells were associated with microvascular basal lamina changes including irregular thickness, multiple layers and loose association with endothelial cells and pericytes, reminiscent of degenerating or regenerating blood vessels. In conclusion, our ultrastructural study suggests that mast cells contribute to the remodelling of existing vessels by a slow release of granule-stored contents in advanced gastric adenocarcinomas. Human mast cells are predominantly found in tissues forming an interface between the host and external environment, such as skin, respiratory and gastrointestinal mucosa. Mast cells are also localized around blood vessels and often close to nerves. Two types of human mast cells have been identified based on their composition of neutral proteases (1). TC mast cells contain tryptase, chymase, mast cell carboxypeptidase and cathepsin G in their secretory granules and are the predominant type of mast cells in the skin and the gastrointestinal submucosa. T mast cells contain only tryptase in their granules and are the predominant type of mast cells in gastrointestinal mucosa and alveolar walls of the lung (1,2). Employing ultrastructural techniques, Craig et al. (3) have shown that TC mast cell granules more often exhibit crystalline structures of the lamellar, lattice and grated type, whereas in T mast cell granules, the discrete scroll-type morphology predominates. These morphological findings thereby permit T and TC mast cells to be distinguished by ultrastructure alone (3).