Patterns of MSI2 expression. (A) MSI2 protein expression was usually present in relatively infrequent cells scattered in an interstitial pattern. (B) Occasional cases showed positive MSI2 staining in confluent sheets of cells. (C) A “watershed” interface was frequently present at the edge of confluent sheets of MSI2-positive cells, and the positive cells merged with negative adjacent cells at an irregular interface. (D) Confluent sheets of MSI2-positive cells were frequently paratrabecular. (E) Admixed non-neoplastic cells, particularly myeloid and erythroid precursors, and megakaryocytes, were negative for MSI2. (F) Occasional cells showed strong nuclear MSI2 staining and weak cytoplasmic staining, but these were infrequent, whereas frequently large blasts showed strong to medium cytoplasmic staining and weak or negative nuclear staining (G). (A-G) Original magnification ×600. Micrographs were imaged using a Nikon Eclipse 80i microscope, with a Nikon Plan APO 60×/1.40 oil objective under oil and captured using a Nikon DS-F digital camera with NIS-Elements D 3.1 software, with manipulation in CorelDRAW X3.