ESR1 and breast cancer: In this study, we generated ribo-minus and RNase R-treated RNA sequencing data from estrogen-stimulated MCF7 breast cancer cells, and identified a large number of estrogen-induced circRNAs, among which circPGR was found to promote ER-positive breast cancer cell growth and tumorigenesis by sponging miR-301a-5p to regulate the expression of multiple cell cycle genes.