MPO and myeloid sarcoma: Postoperative histological examination revealed a diagnosis of MS in the primary of the spleen with presence of irregular karyotype cells, with immunohistochemical diffusely strong positivity for CD33 (Fig. 4), partially positivity for CD68, but negativity for CD3, CD20, CD34, CD56, myeloperoxidase (MPO), and naphthol AS-D chloroacetate esterase staining, and with a chromosomal test.