Immunohistochemical Analysis of the Effect of Dienogest on Ovarian Endometriotic Cysts

Dienogest is a novel progestin with potent oral progestational activity that inhibits the clinical symptoms of endometriosis. We herein evaluated the effect of dienogest on ovarian endometriotic cysts via immunohistochemistry. Ovarian endometriotic cyst specimens were collected from 12 patients treated with dienogest and 20 patients not treated with hormones (controls). The expression of estrogen receptor (ER)-α, progesterone receptor A (PRA), and Ki-67 was studied by immunohistochemistry. As compared with the controls, the cell proliferation index was significantly reduced in both epithelial and stromal cells of the endometriotic cysts following the use of dienogest (P = 0.022 and P = 0.004, respectively). However, there was no significant difference between endometriotic cysts with and without the use of dienogest in the expressions of ER-α and PRA in the epithelial and stromal cells. Irrespective of the use of dienogest, the expression levels of ER-α and PRA in the epithelial cells were low (median: 32% and 8%, respectively). Conversely, the expression levels of ER-α and PRA in the stromal cells were well preserved (median: 68% and 92%, respectively). In the controls, there was no significant difference between endometriotic cysts in the expression levels of Ki-67, ER-α and PRA in epithelial and stromal cells during the proliferative and secretory phases. The finding of a reduction in the cell proliferation index by the use of dienogest with no change in the expressions of hormonal receptors may not support the direct progestational effect of dienogest on ovarian endometriotic cysts.