Findings obtained with bone marrow biopsy and cytospin analysis of the cerebrospinal fluid in the second case. The bone marrow biopsy demonstrated an infiltration of neoplastic cells (A, hematoxylin and eosin staining, ×400) with weak positivity for CD4 and strong positivity for CD56 (B, ×400) on immunohistochemical staining. Cytospin analysis of the cerebrospinal fluid showed neoplastic cells with at frequency of 92.0% (C, Wright staining, ×400); immunocytochemical staining for both CD56 and CD123 (D, ×400) demonstrated positive neoplastic cells.