We monitored WT and STAT1-/- 129S6/SvEv-strain female mice for tumor development and found that 65% (15 out of 23) of the STAT1-/- mice developed spontaneous mammary adenocarcinomas (median tumor onset of 23 months) but that none of the WT mice developed the disease (Figure 3A). This evidence concerns the gene STAT1 and breast adenocarcinoma.