SPI1 and acute promyelocytic leukemia: As shown in Figure 1, PU.1 expression was significantly lower in the primary APL samples in comparison to normal hematopoietic cells, including white blood cells (WBCs), mononuclear cells (MNCs), granulocytes and immature progenitor cells (p = 7.6 × 10-7, 4.6 × 10-4, 1.5 × 10-7 and 0.015, respectively).