To determine whether ERRα inhibition could also affect the growth of tumours that had already acquired lapatinib resistance in vivo, we transplanted an MMTV-NIC ErbB2-driven mammary tumour that had relapsed following lapatinib treatment (Fig. 2g–i) into the mammary fat pads of immunocompetent, coisogenic MMTV-Cre transgenic mice. This evidence concerns the gene ESRRA and breast cancer.