We therefore set out to look at the MRS signature of the action of 17-AAG in spontaneous, mammary tumours in transgenic MMTV-NEU-NT mice where the tumors that arise are driven by the activated form of the NEU/HER2 oncogene and are addicted to it, similar to ERBB2 amplified breast cancer in the clinic. Here, ERBB2 is linked to breast cancer.