**Core Concept**
Postmenopausal bleeding is a clinical presentation that warrants a thorough investigation, particularly in the context of a new diagnosis of endometrial adenocarcinoma. The management of endometrial cancer involves a multidisciplinary approach, including surgical, medical, and radiation oncology.

**Why the Correct Answer is Right**
The most appropriate next step in management for a patient with grade I endometrial adenocarcinoma is to perform a hysterectomy. This is because grade I endometrial adenocarcinoma is typically an early-stage cancer with a good prognosis, and surgical staging with a hysterectomy provides the most accurate histopathological diagnosis and allows for the removal of the primary tumor. Additionally, a hysterectomy addresses the patient's underlying cause of postmenopausal bleeding and eliminates the risk of recurrence.

**Why Each Wrong Option is Incorrect**
**Option A:** Preoperative chemotherapy or radiation therapy is not typically indicated for grade I endometrial adenocarcinoma, as it is an early-stage cancer with a good prognosis.
**Option B:** A simple endometrial biopsy is insufficient for staging endometrial cancer, and a more comprehensive surgical staging procedure is required.
**Option C:** Medical management with hormone therapy or chemotherapy is not the primary treatment for grade I endometrial adenocarcinoma and may not address the underlying cause of postmenopausal bleeding.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that postmenopausal bleeding is a red flag symptom that warrants a thorough investigation, including endometrial sampling and imaging studies, to rule out endometrial cancer.

**Correct Answer:** C. Total hysterectomy.