0.2-0.5 g of frozen LM and matched MM tissues were used for ChIP-seq. Tissue was finely grounded with mortar and pestle in liquid nitrogen, followed by fixation in 1% paraformaldehyde for 15 min and quenching with 1X glycine for 5 minutes at room temperature. Chromatin was isolated using the SimpleChIP Enzymatic Chromatin IP Kit (Cat no: 9003S, Cell Signaling Technology, Danvers, MA) following the manufacturer's protocol. 15 µg of chromatin was incubated with 6 µg of each of the antibodies against PR, MED12, or ERα to immunoprecipitate the target protein-bound DNA, which was then purified for library preparation. The libraries were prepared using the KAPA Hyper Prep Kit (Cat no: KK8502, KAPA Biosystems) and KAPA Single-Indexed Adapter Kit (Cat no: KK8722, KAPA Biosystems). The libraries were sequenced as 75 bp single-end for 40 million reads per sample at Northwestern University's NUSeq Core using the NextSeq 500 system (Illumina, San Diego, CA).