The investigation of choice in a 55-year-old postmenopausal woman who has presented with postmenopausal bleeding is:

Post menopausal bleeding most commonly occurs due to atrophic changes but can also occur due to Ca endometrium or Ca cervix. Hence, in case of post menopausal bleeding, ruling out both endometrial and cervical cancer is always a priority. Hence, a fractional curettage is the right choice. TVS can detect uterine pathology, but histopathological diagnosis is necessary in this case. Pap can be done, but it is positive only in 30-50% of cases of Ca endometrium. Ca-125 estimation is for ovarian carcinoma. Ref: TeLinde's Operative Gynaecology, 9th Edition, Page 1379 ; Dutta Gynaecology, 4th Edition, Page 331 ; Oxford Handbook of Surgical Specialities, 6th Edition, Page 10