ERBB2 and neoplasm: By breeding transgenic mice expressing ErbB2 from the MMTV promoter (MMTV-ErbB2) with a transgenic mouse line to express the gene encoding the Cre recombinase from the WAP promoter (and therefore to mark WAP+ cells), Henry et al. [9] have discovered evidence that WAP+ cells are the cell of origin of tumor initiated by the MMTV-ErbB2 transgene, which is also supported by Jeselsohn et al. [10].