A 52-year-old woman with a history of a bilateral oophorectomy presents to the nurse practitioner with complaints of vaginal bleeding and pelvic pain for 2 weeks. What is the best next step?

Choice A reason: Referral to an oncologist is premature without diagnostic confirmation of malignancy. Choice B reason: CA-125 is mainly used for ovarian cancer, which is unlikely after bilateral oophorectomy. Choice C reason: Pap smear screens for cervical cancer and is not indicated for evaluating postmenopausal or post-oophorectomy bleeding. Choice D reason: Correct. Endometrial biopsy or transvaginal ultrasound helps evaluate uterine pathology, including endometrial cancer, and is the most appropriate initial diagnostic step.