Small Early Gastric Cancer with Special Reference to Macrophage Infiltration

The authors investigate the tumor-infiltrating cells in small early gastric cancer (EGC) (<10 mm) and describe the ultrastructural features and interactions of macrophages with tumor cells and other inflammatory cells. Sections from 20 small EGCs were stained by immunohistochemical methods for CD20, UCHL1, CD4, CD8, and CD68 (electron microscopic examination was used in 6 of the 20). In all of the tumors, CD68-positive macrophages accounted for most tumor-infiltrating cells, with UCHL1-positive T lymphocytes, eosinophils, and neutrophils being the next most frequent. We found only a few CD20-positive B lymphocytes. Electron microscopic analysis revealed macrophages with many phagocytic vesicles, cellular debris, and apoptotic bodies. These morphologic data show that macrophages are actively phagocytic. The tumor cells in contact with macrophages showed no cytopathic changes. These data do not support a macrophage-mediated cancer lysis like the ones reported in some systems in vitro. Contacts among macrophages and other inflammatory cells formed a recurrent ultrastructural hallmark and suggest a communication among varying inflammatory cell types during the precocious host response to gastric neoplasia.