ESR1 and breast cancer: A particularly instructive model has been provided by the regulation of a large program of acute ligand-dependent enhancer activation in breast cancer cells (MCF7), causing the rapid assembly of RNP complexes, referred to as the MegaTrans complex, at the ~1–2000 most robustly activated ERα-bound enhancers with RNP condensate-like properties controlling E2-regulated transcriptional programs25,41.