The CBA inbred mouse strain is a model of radiation-induced acute myeloid leukemia (rAML) [8, 9] where hemizygous interstitial deletion of chromosome 2 (Del2) is a characteristic finding [10] with the minimal deleted region (MDR) containing Sfpi1, encoding the hematopoietic transcription factor PU.1 [11]. The gene discussed is SPI1; the disease is acute myeloid leukemia.