Fig. 1

Morphologic and immunohistochemical evaluation of diagnostic bone marrow aspirate and core biopsy. Diagnostic bone marrow aspirate (a and b, Wright-Giemsa, 600x) and biopsy (c, h & e, 200x) showing myeloid elements at all stages of maturation. The aspirate shows that blasts are not markedly increased and cells with cytology consistent with lymphoblasts are not readily apparent. Eosinophils (green arrows), basophils (arrowhead) and dwarf megakaryocytes (black arrows) are identified. Immunohistochemical staining of the bone marrow biopsy (100x) shows an expansion of CD34(subset) + TDT+ blasts (d and e, respectively) that form clusters. An expansion of CD3+ T-cells (f) without an expansion of CD19+ B-cells (g) is seen. In panel h, double staining of the biopsy (400x) shows that MECOM expressing cells (brown nuclear stain) are distinct from CD3+ T-cells (red membranous stain)