The World Health Organization's histologic classification of gastrointestinal tumors. A commentary on the second edition. The World Health Organization's (WHO) histologic classification of gastrointestinal tumors has been revised. Although the general basis of classification and the overall outline remain similar to the first edition, advances in the last decade justified changes in classifying certain entities; among them were malignant lymphomas, endocrine tumors, and dysplasias. Several newly recognized entities have also been added. 