BACKGROUND:Gestational trophoblastic disease (GTD) is a heterogeneous group of disorders characterized by abnormal trophoblast tissue.Molar and non-molar hydropic placental changes are the most common forms of GTD.Differential diagnosis of GTD is sometimes problematic.Recently,p53 expression was identified as a good marker for distinguishing GTD types.AIMS:Comparison of p53 expression in partial hydatidiform mole (PHM) and hydropic abortion.METHODS:In this prospective cross-sectional study,molar and non-molar hydropic pregnancy specimens were collected.Immunohistochemical staining,based on the Labeled Streptavidin Biotin (LSAB) technique,was carried out on multiple 4 μm paraffin block sections prepared from formalin-fixed trophoblastic tissues.Polymer-based Envision was used to assess p53 tumor suppressor protein immunoreactivity.p53 expression was then compared between both groups.RESULTS:In the study,40 patients were included:20 with confirmed PHM and 20 with hydropic pregnancy.p53 protein was positive in 60％ of patients with PHM and 25％ of patients with hydropic pregnancy.The p53 positive rate was significantly higher in patients with PHM (p =0.027).Moreover,patients with PHM had a significantly high grade of staining (p ＜ 0.001).CONCLUSION:Our findings indicate that immunohistochemical analysis of p53 protein can be used to distinguish PHM and hydropic pregnancy.