TREX2 and cancer: Although studies in embryonic stem cells have shown that Trex2 deletion leads to spontaneous chromosomal rearrangements [4] and inactivation of Trex2 exonuclease leads to double strand breaks (DSBs) [5] Trex2 knockout mice (Trex2−/−) do not exhibit a spontaneous cancer-prone phenotype or chromosomal instability [6], as would be expected if TREX2 had a relevant DNA-editing role.