A case of clear cell adenocarcinoma arising from endometriosis of the rectum treated by laparoscopic surgery

•Clear cell adenocarcinoma arising from endometriosis is very rare.•Preoperative diagnosis of the malignant transformation in endometriosis is very difficult.•The patient was undergone low anterior resection under the diagnosis of rectal carcinoma.•Sampson's criteria are useful for diagnosis of the malignant transformation in endometriosis.•The prognosis of malignant transformation in endometriosis is poor.

INTRODUCTIONMalignant transformation of intestinal endometriosis occurring in the extraovarian sites is extremely rare. We report a very rare case of clear cell adenocarcinoma arising from endometriosis of the rectum.PRESENTATION OF CASEAn 83-year-old woman was admitted with the complaint of hematochezia. Colonoscopy revealed a tumor around about half of the rectal circumference. Biopsy of the tumor revealed a well-differentiated adenocarcinoma. Low anterior resection was undergone laparoscopically under the diagnosis of rectal carcinoma. Histopathological examination revealed clear cell adenocarcinoma, invading the sub-serosa of the rectum, but no metastasis of the lymph nodes. Immunohistochemical staining showed strong positivity for cytokeratin 7, but no staining for cytokeratin 20 and CDX2. The tumor existed adjacent to the endometrial glands, which were stained positive for Estrogen receptor. Ultimately, the patient was diagnosed with clear cell adenocarcinoma arising from endometriosis. Eighteen months after surgery, there are no signs of tumor recurrence.DISCUSSIONClear cell adenocarcinoma arising from intestinal endometriosis has been reported in 7 cases, including our case. Careful observation is required because the prognosis of endometriosis after malignant transformation remains poor.CONCLUSIONWe report a very rare case of clear cell adenocarcinoma arising from endometriosis of the rectum treated by laparoscopic surgery.