Glucocorticoid receptor (GR) is a ligand-inducible transcription factor with an intricate role in cancer biology. Using an in silico designed GR activity signature we show that GR is a tumor suppressor across diverse primary cancers. In breast cancer, GR activity status determines luminal identity, and importantly, relates to patients’ outcomes. We illustrate that GR suppresses tumor growth, mediated through its engagement with the estrogen receptor-α (ER). This steroid hormone receptor cross-talk leads to redistribution of ERα on chromatin, ultimately leading to expression of ZBTB16 gene. We define ZBTB16 as a transcriptional repressor and a tumor suppressor in ER-positive breast cancer. Importantly, highly aggressive ER-positive breast cancer cells displaying absence of GR activity can be eradicated if GR-induced gene repression is mimicked by inhibitors of the epigenetic pathway. In line with this, epigenetic regulators are highly expressed upon GR activity loss, leading to vulnerability of aggressive breast cancer cells to clinically available epigenetic inhibitors. Our findings indicate that GR functions as a tumor suppressor by repositioning ER to specific sites on chromatin, modulating targetable pathways, which has important implications for patients’ prognosis and therapeutic interventions.