Classifying tumour samples by subtypes, i.e. “luminal”, “HER2-enriched” and “triple-negative breast cancer (TNBC)” [37], based on immunohistochemistry (IHC) and fluorescence in situ hybridisation (FISH) data for oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), revealed a significant (P < 0.05) up-regulation of AGR3 mRNA expression in luminal breast tumours (Fig. 1B). This evidence concerns the gene PGR and triple-negative breast carcinoma.