Clear cell adenocarcinoma of the ovary arising in atypical endometriosis: a report of eight cases

Introduction Studies of clear cell adenocarcinoma of the ovary (CCAO) arising from endometriosis are scant. Materials and methods The author reviewed 13 cases CCAO of our pathology laboratory for the presence of endometriosis within the tumor. Eight (61.5%) of the 13 tumors contained endometriosis within the tumor. Of the eight cases, seven were atypical endometriosis and one was ordinary endometriosis. The age of the eight patients with CCAO ranged from 35 to 82 years with a median of 52 years. Results Grossly, the ovarian tumors of CCAO were characterized by unilocular cystic lesions containing solitary or multiple nodules in the inner surfaces. The outer surface was smooth and free of tumor. Histologically, the nodules showed typical features of pure CCAO with clear cells, hobnail cells, and hyalinized stroma. The non-nodular flat areas of the tumor were composed of a layer of atypical clear cells and endometriosis consisting of a layer of endometrial epithelium and endometrial stroma. Incipient foci of CCAO were occasionally recognized in the atypical clear cells. Seven cases with endometriosis showed atypia of the endometrial epithelium (atypical endometroiosis), and one case showed no atypia. There was contiguity between the CCAO and atypical clear cells and between atypical clear cells and endometriosis. Contiguity between atypical endometriosis and CCAO was also recognized in a few areas. The outer surface was devoid of tumor cells and endometriosis. Conclusions The author speculates as follows. An endometrial cyst develops in the ovary. Its epithelium undergoes initiation, thus giving rise to atypical endometriosis consisting of dysplastic or intraepithelial neoplastic epithelium. The atypical endometriosis further undergoes initiation, leading to the atypical clear cells, and ultimately leads to CCAO showing a unilocular cyst consisting of inner masses of CCAO and flat areas composed of a layer of atypical clear cells with incipient CCAO and atypical endometriosis.