Comments on the 5th edition of WHO classification of digestive system tumors - Part 1. Gastrointestinal tract.

The new 2019 WHO classification of digestive system tumors reflects some important advancements in our understanding of etiopathogenesis and molecular background of selected neoplastic diseases of the gastrointestinal tract, offers more integrated review of non-epithelial neoplasms and updates the spectrum of genetic tumor syndromes of the digestive system. Recently recognized conditions, such as gastroblastoma and “gastric adenocarcinoma and proximal poly-posis of the stomach” are described, including molecular alterations associated with these entities. On the other hand, the new interpretation of some topics, mainly grading of serrated lesions or ICD-O coding of adenomas and dysplasia, is rather controversial. Last but not least, the definition of pTis in the large intestine according to WHO conflicts its definition according to AJCC/UICC TNM classification, 8th edition, issued in 2017.