Clear cell adenocarcinoma present exclusively within endometrial polyp: report of two cases.

Endometrial polyp is a common benign lesion that protrudes into the endometrial surface. The incidence of carcinoma within endometrial polyp is thought to be low, however, postmenopausal women with endometrial polyps are at an increased risk. Endometrial clear cell adenocarcinoma is a distinct and relatively rare subtype of endometrial carcinoma, and recent studies have proposed putative precursor lesions of clear cell adenocarcinoma, namely clear cell endometrial glandular dysplasia (EmGD) and clear cell endometrial intraepithelial carcinoma (EIC). Herein, we describe two cases of clear cell adenocarcinoma present exclusively within endometrial polyp and discuss the association of its precursor. Two postmenopausal Japanese females, 66-year-old (Case 1) and 54-year-old (Case 2) presented with abnormal genital bleeding. Cytological examination of both cases revealed adenocarcinoma, thus, hysterectomy was performed. Histopathological studies demonstrated clear cell adenocarcinoma within exclusively endometrial polyp in both cases. The peculiar finding in Case 1 was presence of atypical glandular cells with large round to oval nuclei and clear cytoplasm within the atrophic endometrial glands in the surrounding endometrial tissue, which corresponded to clear cell EIC. A recent study showed that 33% of uteri had at least one focus of clear cell EmGD in endometrial polyps. Accordingly, clear cell adenocarcinoma and clear cell EmGD can occur in association with endometrial polyps more frequently than previously thought. Therefore, detailed histopathological examination is important in diagnosis of endometrial polyps, especially in the postmenopausal women, moreover cytological examination is a useful tool in the postmenopausal women with endometrial polyps.