However, the prevalence of cases with weak ER expression (i.e. in between 1 and 9%) is exceedingly low in the ESME cohort, accounting for only 0.8% of all histologies, in accordance with data from the literature20 and from French GEFPICS registry (1.4% among 14,000 invasive breast cancer, own unpublished data). This evidence concerns the gene ESR1 and invasive breast carcinoma.