Identification of neoplastic Paneth cells in an adenocarcinoma of the stomach using lysozyme as a marker, and electron microscopy.

A large number of cells containing large eosinophilic granules in their supranuclear cytoplasm was observed in a well differentiated adenocarcinoma of the stomach and its metastases. These cells were identified as Paneth cells by electron microscopy and by their content of lysozyme. Lysozyme-immunoreactivity was well preserved after fixation of tumor tissue in liquid formaldehyde followed by postfixation in osmium tetroxide. Immunoreactivity at immunoelectron microscopy was confined to the large osmiophilic secretory granules. We conclude that morphologically and biochemically differentiated Paneth cells occasionally occur in neoplasms of the gastrointestinal tract.