Within the histiocytic/dendritic cell neoplasms, “blastic plasmacytoid dendritic cell neoplasm (BPDCN)” has been added to the group of “plasmacytoid dendritic cell neoplasms”, and the entities “mature plasmacytoid dendritic cell proliferation associated with myeloid neoplasm (MPDCP)”, “Rosai-Dorfman disease”, and “ALK-positive histiocytosis” were newly included. This evidence concerns the gene ALK and CD4+/CD56+ hematodermic neoplasm.