Clear Cell Adenocarcinoma of the Colon Arising in the Background of Endometriosis: A Case Report and Diagnostic Approach

Clear cell adenocarcinoma of the colon is rare, with only a handful of cases reported in the literature. Some of these cases are attributed to endometriotic involvement of the colonic wall; however, a presence of the clear cell adenocarcinoma and endometriotic glands with dysplastic clear cell changes in the colonic wall has not been compellingly demonstrated. We describe a case of clear cell adenocarcinoma of rectosigmoid in a 41-year-old woman, where we have been able to document endometriotic glands with dysplastic clear cell transformation in the background. The presence of the endo- metriotic glands and the endometrial stroma is confirmed with immunohistochemical stains. The diagnostic approach and immuhistochemi- cal characteristics of these neoplasms are discussed along with difficulties in staging of these tumors.