ERBB2 and breast cancer: The NTTg mouse, a transgenic animal model carrying the unactivated rat HER2 (Human Epidermal Receptor 2)/neu protooncogene (NeuN) and the mouse mammary tumor virus (MMTV) promoter, presents a similar disease phenomenon to breast cancer and has a prolonged latency of tumorigenesis and growth, with late occupancy of metastasis [19,20].