As a side note, unique sets of genes up or down-regulated by PRA-PRA, PRB-PRB, and PRA-PRB have been mapped in Hec50co endometrial cancer cells and, from these, endometrial cancer cells expressing both PR isoforms (where heterodimers are possible) have reportedly shown about a tenfold more robust genomic response to progesterone, with over 10× genes found to be regulated by PRA + PRB when compared to the number of genes regulated by PRB and PRA alone (communications with Dr. K. Leslie, also see12 and references therein). The gene discussed is RB1; the disease is endometrial cancer.