PGR and cancer: Additionally, consistent with our finding of rapid PR protein loss (i.e., by turnover) of activated (deSUMOylated and phosphorylated) receptors, we detected phospho-PR gene signatures in breast tumors clinically designated as PR-low to PR-null (luminal B) and identified novel gene sets (HER2, PAX2, AHR, AR, and RUNX) uniquely regulated by modified PRs that are associated with cancer stem cell biology.