ERBB2 and breast carcinoma: To further investigate the interplay between RTK signalling and ERRα activity in breast cancer, we quantified the level of ERRα-positive nuclear staining in breast tumour samples from various subtypes using a specific antibody for ERRα (Supplementary Fig. 1a) and observed that the HER2-positive/oestrogen receptor-negative tumours express the highest level of ERRα-positive nuclei with a median expression of 90% (Fig. 1a, one-way analysis of variance P value=0.0487).