MKI67 and choriocarcinoma: As described in most of previous studies (14, 20-23), there was no immunostaining for Ki-67 in the nuclei of syncytiotrophoblasts, however Erfanian et al reported that Ki-67 expression was observed in syncytiotrophoblastic cells of abortion, partial hydatidiform mole, complete hydatidiform mole and choriocarcinoma (12).