Malignant Gastric Tumours: The Role of Pathologist in the Diagnosis and for Therapeutic Decisions

Abstract

This chapter gives an overview about the most important malignant gastric tumours from the perspective of the pathologist. The first focus is the systematic classification of gastric carcinoma, neuroendocrine tumours, mesenchymal tumours and malignant lymphoma with related histomorphology-based and molecular-based diagnosis criteria including differential diagnosis pathologists have to consider when dealing with gastric tumours. The second focus addresses the issues of personalized therapy options in gastric tumours pathologists have to bear in mind. Currently, some subtypes of gastric adenocarcinomas have been proposed with therapeutic implications like microsatellite-instable carcinoma and checkpoint-inhibition or Her2/neu positive adenocarcinoma of intestinal-type and specific tyrosine-receptor blockade. Mesenchymal tumours are rare and can morphologically be quite variable. Mucosa-associated lymphoid tissue (MALT)-related marginal zone lymphoma is the most frequent gastric lymphoma but all other B-and T-cell lymphoma can occur in the stomach as well, and an exact subcharacterisation is very important due to different treatment decisions (e.g. eradication of helicobacter-pylori in MALT-lymphoma as first choice treatment vs. chemotherapy in Burkitt-lymphoma). Pathologists have to consider a large spectrum of differential diagnosis and conflicting immunohistochemical and molecular results. It will become more and more important to find out therapeutically relevant tumour subtypes and to use biomarkers to predict a successful individualized treatment.