NCAM1 and CD4+/CD56+ hematodermic neoplasm: However, in 2008, the World Health Organization described BPDCN as a type of acute myeloid leukemia (AML), and in the 2016 revision, it was classified as its own entity.[1,2] BPDCN is characterized by the expression of CD4, CD56, and the pDC-specific associated antigens CD123, TCL-1, and CD303 on its cell surface.