BACKGROUND: Ovarian cancer arising from an endometriotic cyst in a postmenopausal woman under tamoxifen therapy is rare. CASE: We herein report the case of a 67-year-old woman with a history of breast cancer, taking tamoxifen citrate 20 mg/day for 4 years, who underwent an operation for left ovarian tumor. The postoperative histological diagnosis was endometrioid adenocarcinoma in an endometriotic cyst with a gradual transition of the degree of cellular atypia noted from typical endometriotic epithelium, to atypical endometriosis, and finally to adenocarcinoma. CONCLUSION: Tamoxifen may cause malignant transformation of endometriosis through atypical endometriosis even in the postmenopausal state. Atypical endometriosis may act as a precancerous lesion in the process of tamoxifen-induced malignant transformation of endometriosis.
BACKGROUND: Ovarian cancer arising from an endometriotic cyst in a postmenopausal woman under tamoxifen therapy is rare. CASE: We herein report the case of a 67-year-old woman with a history of breast cancer, taking tamoxifen citrate 20 mg/day for 4 years, who underwent an operation for left ovarian tumor. The postoperative histological diagnosis was endometrioid adenocarcinoma in an endometriotic cyst with a gradual transition of the degree of cellular atypia noted from typical endometriotic epithelium, to atypical endometriosis, and finally to adenocarcinoma. CONCLUSION:Tamoxifen may cause malignant transformation of endometriosis through atypical endometriosis even in the postmenopausal state. Atypical endometriosis may act as a precancerous lesion in the process of tamoxifen-induced malignant transformation of endometriosis.