MPO and neoplasm: For the final diagnosis, immunohistochemistry (IHC) was performed, and the tumor cells tested positive for MPO, CD4, BCL-2, KI-67 (Fig. 3), and CD117 and negative for CD3, CD5, CD20, CD56, bcl-6, Mum-1, CD123, MUM-1, TdT, Syn, SOX11, and C-myc.