Objective To investigate the degree of fibrosis,the expression of estrogen and progesterone receptors,and the expression of angiogenesis-related molecules in polypoid endometriosis,with the aim of further elucidating its histopathological characteristics.Methods The study retrospectively analyzed the clinicopathological data of 42 patients diagnosed with polypoid endometriosis through surgical treatment at Obstetrics and Gynecology Hospital,Fudan University from Apr 2014 to Aug 2020.Additionally,tissue samples from 19 cases of ovarian endometriotic cysts,20 cases of adenomyosis,20 cases of deep infiltrating endometriosis,and 20 cases of endometrial polyps,all pathologically confirmed,were collected as a control group.The degree of fibrosis,the expression of estrogen and progesterone receptors,and the expression of angiogenesis-related molecules in the lesions of each group were determined using Masson staining and immunohistochemistry.Results The mean age of onset of the 42 patients with polypoid endometriosis was 41.24 years.And the most usual clinical manifestation is pelvic mass(24/42 patients).Immunohistochemical experiments showed that polypoid endometriosis was less fibrotic than ovarian endometriotic cysts,adenomyosis and deep infiltrating endometriosis but more fibrotic than endometrial polyps.Polypoid endometriosis also has a higher vascular density,increased expression of estrogen receptor-β(ER-β),and down-regulated expression of progesterone receptor B(PR-B).Conclusion Polypoid endometriosis is a distinct subtype of endometriosis characterized by a lower degree of fibrosis,higher levels of estrogen receptor expression,and relatively rich vascularization,generally associated with a favorable prognosis.