To test whether overexpression of RAC1B promotes tumour invasion, we crossed Apc p53 mice with mice carrying an inducible overexpression allele of human RAC1B in the Rosa26 locus (VillinCreERT2Apcfl/+TP53fl/flRosa26lsl-hRAC1B/lsl-hRAC1B, referred to from now on as Apc p53 Rac1b) (Fig. 1B). Here, APC is linked to neoplasm.