The documented spontaneity and latency (4, 5) of tumourigenesis in these MMTV-based HER2 transgenic models also make them impractical for rapidly testing and optimizing more complex regimens (e.g. combination therapies), or for evaluating HER2-targeted therapies in other HER2-overexpressing malignancies with divergent underlying oncogenic drivers (e.g. gastric cancer, ovarian cancer). Here, ERBB2 is linked to gastric cancer.