Ultrastructural Evidence of Eosinophil Clustering and ETosis in Association with Damage to Single Tumour Cells in a Case of Poorly Cohesive NOS Gastric Carcinoma

A case of poorly cohesive NOS gastric carcinoma, characterised by high-grade tumour-associated tissue eosinophilia (TATE), is studied by transmission electron microscopy. Eosinophil clustering around single tumour cells constituted a recurrent ultrastructural hallmark. Some eosinophils were in intimate contact with tumour cells and exhibited extracellular trap cell death (ETosis): a non-apoptotic cell death process, recently described in non-neoplastic, eosinophil-associated diseases. Discharge of chromatin material and specific granules, due to eosinophil ETosis, was polarised towards single tumour cells that showed various degrees of cytopathogenic changes. Our data suggest that eosinophil ETosis may exert an antitumoural activity in gastric cancer. LEARNING POINTS: A recent meta-analysis reported that TATE is a histopathological marker of favourable prognosis, particularly in patients with gastrointestinal cancer. Experimental studies have shown that eosinophils may exert antitumour activity through discharge of their highly cytotoxic granular proteins. Our ultrastructural findings add novel mechanism insights for eosinophil antitumoural activity, providing morphologic evidence of eosinophil ETosis in association with single tumour cell injury.