Yang CF, et al. - The purpose of this study was to distinguish between aggressive natural killer (NK)-cell leukaemia (ANKCL) and extranodal NK/T-cell lymphoma (ENKTCL) with secondary bone marrow involvement. The bone marrow NK/T-cell neoplasms were examined by classifying them into those with no extramedullary mass (group 1) and those with extramedullary mass (group 2). It was observed that all of the group 1 patients fulfilled the World Health Organisation 2017 diagnostic criteria of ANKCL, and their survival was significantly worse than that of the group 2 patients. Therefore, ANKCL with no extramedullary mass ought to be distinguished from ENKTCL with bone marrow involvement, as the former exhibited distinct outcomes and genetic features.