Neoplasms of uncertain behaviour, except of lymphoid, haematopoietic, central nervous system or related tissues

**Definition:** A neoplasm except of lymphoid, haematopoietic, central nervous system or related tissues displaying morphologic, phenotypic, or genotypic characteristics that are clearly not benign but do not permit the establishment of a definitive diagnosis of malignancy. Such neoplasms may or may not eventually have a more aggressive clinical course. Representative examples include borderline ovarian epithelial neoplasms (e.g., borderline ovarian endometrioid tumour and borderline ovarian mucinous tumour), borderline exocrine pancreatic neoplasm (e.g., pancreatic borderline intraductal papillary-mucinous neoplasm), and primary borderline peritoneal epithelial neoplasm.