STAT1 and cancer: Although we found rare mutations in known cancer genes, such as Cbl, Mybl2, and Stat1, we found no recurrent tier 1 mutations amongst the 16 samples, suggesting that additional acquired mutations may not be required to release the leukemic potential of NP23-NHD13 hematopoietic cells, and that concurrent expression of NP23 and NHD13 in the mouse thymus may be sufficient for trans-differentiation and malignant transformation (Supplementary Table S5).