Image 2.

Patterns of GATA binding factor 1 (GATA1) expression in mastocytosis and chronic myelogenous leukemia (CML). A, In this bone marrow core biopsy specimen of a patient with systemic mastocytosis, the neoplastic mast cells, including spindle forms, are highlighted by intense to intermediate nuclear GATA1 staining (×40). B, In this bone marrow core biopsy specimen of a patient with CML, GATA1 reactivity is largely absent in the neoplastic myeloid cells (×40). However, rare cells, some with bilobed nuclei (see inset), are weakly positive for nuclear GATA1, likely representing eosinophilic myeloid elements. Also noted are erythroid precursors with intense nuclear GATA1 staining as a useful internal positive control.