ESR1 and cancer: Transcript overexpression occurs through transcriptional and epigenetic control mechanisms in the vast majority of cancers, as demonstrated by Rinath et al., who uncovered a role for the RUNX2-ER (runt-related transcription factor 2-estrogen receptor) complex in stimulating the transcription of a set of genes, including most notably the stem cell factor Sox9, which promotes proliferation and a metastatic phenotype [14], and TRIM28, which interacts with EZH2 and SWI/SNF to activate genes that promote mammosphere formation [15].