In the context of endometrial cancer, this is a potential ideal scenario that would titrate growth factor activation of MAP Kinase activity to promote phosphorylation of both PR isoforms, inducing translocation of phosphorylated PRB to the nucleus and formation of ligand-bound heterodimers, without loss of most active dimers to ubiquitin-mediated degradation. This evidence concerns the gene RB1 and endometrial cancer.