A 52-year-old woman from Mumbai presents with postmenopausal bleeding and pelvic pain for 4 months. She has a history of Lynch syndrome (MLH1 mutation). Pelvic MRI shows a large endometrial mass with invasion into the outer myometrium and parametrial involvement. Endometrial biopsy confirms grade 3 adenocarcinoma. She is counseled about staging and adjuvant therapy. Which of the following is the MOST appropriate next step in management?