ESR1 and breast cancer: ER∆7 was the highest expressed variant among those tested, which is in line with previous observations.13 We found very low mRNA expression values of the ER variant ERα-36, which has been described as a mediator of the ER non-genomic signaling pathway.14 This partly conflicts with a previous study reporting, based on ERα-36 protein expression using a custom antibody, high expression of this variant in a significant subset of ER-positive breast cancers.22