Researchers showed that ES-2 cells expressing progesterone receptor (PR), PEO4 cells positive for the PR and estrogen receptors, and primary ovarian cancer cells, displayed various features of senescence, including growth arrest in the G1 phase of cell cycle, an enlarged morphology, an expression of SA-β-Gal, and upregulated levels of p21Cip1 upon the experimental stimulation of the PR. The gene discussed is PGR; the disease is ovarian cancer.