PKNOX1 and cancer: PREP1 (Pbx-regulating protein 1, aka PKNOX1), and MEIS1 (Myeloid ecotropic insertion site 1) are transcription factors belonging to the three amino acids loop extension (TALE) homeodomain family1, and play essential roles during embryonic development and cancer by associating to pre-B-cell leukemia (PBX) cofactors2,3.