RAG2 and cancer: While immune-deficient nude mice, which display a markedly reduced amount of T-cells, do not show an increased rate of tumors (4), specifically genetically modified mice with knock-outs of recombination activating gene 2, signal transducer and activator of transcription 1 (STAT1); or the gamma-interferon receptor show increased cancer rates even if not treated with carcinogens or crossed with animals with a cancer development stimulating mutation (5, 6).