To this end, we used immunocompetent, transgenic C57BL/6‐Her2 mice that are fully tolerant of, and constitutively express human Her2 in breast epithelium and cerebellar cortex, and are also permissive for the growth of Her2 expressing tumours of C57BL/6 origin.14, 15. This evidence concerns the gene ERBB2 and neoplasm.