In the most comprehensive study of potential markers useful in the distinction between grade 3 endometrioid carcinoma and serous carcinoma published to date, Han et al. 3 analyzed the diagnostic role of 12 proteins (ER, PR, p16, p53, Ki-67, PTEN, beta-catenin, vimentin, IMP3, TFF3, ARID1A, and HNF1B) in this differential diagnosis. The gene discussed is PGR; the disease is endometrioid adenocarcinoma.