Case report: a Lynch syndrome patient with vaginal endometriosis-associated malignancy and synchronous colon tubulovillous adenoma

Ting KuangXiaoping LiuQI LIZiqian TangXidie LiJinjin WangHuan Chen^*

• Zhuzhou Central Hospital, Zhuzhou, China

Endometriosis is a common gynecological condition. However, endometriosis-associated malignancy occurs in up to 1% of women with endometriosis. Most cases of endometriosis-associated malignancy occur in the ovary, while 20% occur in extragonadal sites.We report the case of a patient with an incidental finding of vaginal endometriosis-associated malignancy, who was later diagnosed with Lynch syndrome due to MSH6 deletion with loss of protein expression, and subsequently found to have a high-grade colonic tubulovillous adenoma. The patient was a 50-year-old woman without any previous history suggestive of adenomyosis or endometriosis, who was examined at a local hospital and found to have a swelling in the posterior vaginal fornix. A colposcopy was performed, and the mass was biopsied, revealing an endometrial adenocarcinoma. She was then transferred to our hospital, where, after a series of assessments, she underwent surgery (including total hysterectomy, double adnexectomy, partial vaginal hysterectomy, and lymph node dissection). Postoperative pathological examination indicated a diagnosis of vaginal endometriosis-associated malignancy. A paclitaxel/carboplatin regime chemotherapy regimen was initiated at nine days postoperatively. Losses of MSH6 protein expression in the mass was observed by postoperative immunohistochemistry. Genetic sequencing revealed pathogenic MSH6 variants, including p.F1104Lfs*11(c.3312delT) and c.3556+1G>A, indicating germline mutations. These findings both suggest the presence of Lynch syndrome. Before the second postoperative chemotherapy, the patient underwent a colonoscopy and a mass measuring approximately 6 cm in diameter was identified in the right half of the transverse colon. One month after the second cycle of chemotherapy, the patient underwent laparoscopic radical right hemicolectomy. Histopathological examination revealed a tubulo-villous adenoma with high-grade intraepithelial neoplasia of partial glands. One month after the second surgery, the patient was referred to our department and completed four cycles (total of six) of combination chemotherapy (carboplatin and paclitaxel) and was still recurrence-free at the last follow-up (July 2025). Lynch syndrome with both extra-ovarian endometriosis-associated cancer and intestinal lesions is rare. We report a case of incidentally identified vaginal endometriosis-associated malignancy in a patient with Lynch syndrome due to MSH6 protein deficiency and MSH6 germline mutations and the discovery of a high-grade tubular choriocapillaris adenoma of the colon.