In contrast, when NeuNT was knocked into the endogenous Erbb2 locus, and therefore expressed under the control of the endogenous promoter, MMTV-Cre-dependent activation of expression resulted in mammary hyperplasia and the formation of focal tumours after a long latency (over 1 year) (Andrechek et al., 2000). This evidence concerns the gene ERBB2 and neoplasm.