Our clinical trial NCT03241888 showed LNG-IUS had a better treatment efficacy than Megestrol Acetate (MA) alone. The median CR time for MA group, LNG-IUS group and MA plus LNG-IUS group was 7.0±0.3 months, 4.4±1.0 months and 5.7±1.2 months.

To verify whether metformin could improve the effect of progestin as fertility-sparing treatment in patients with atypical endometrial hyperplasia(AEH).

Whether metformin could improve the effect of progestin as fertility-sparing treatment in patients with atypical endometrial hyperplasia(AEH) is still not clear. Our previous finding from subgroup analysis in a phase II randomized controlled trial showed that 39.6% of AEH patients in metformin plus megestrol acetate group achieved complete response, compared with 20.4% in group of megestrol acetate alone. This trial aim to fully testify the effect of metformin in fertility-sparing treatment for AEH patients with adequate sample size.

Inclusion Criteria:

1. 18-45 years old;
2. pathologically diagnosed with AEH for the first time;
3. desire to preserve their fertility;
4. no signs of suspicious myometrial invasion or extrauterine metastasis by enhanced magnetic resonance imaging (MRI), enhanced computed tomography (CT) or transvaginal ultrasonography (TVUS);
5. no contraindication for metformin, megestrol acetate or pregnancy;
6. no hormone or metformin treatment within 6 months before entering the trial;
7. not pregnant when participating in the trial;
8. willing to follow the trial arrangement after being fully informed of all the risks and inconveniences caused by the trial.

Exclusion Criteria:

Patients who had one or more of the following conditions:

1. allergy history or contraindications for megestrol acetate or metformin;
2. pregnant when initiating the study;
3. alcoholism, severe infection, severe chronical diseases (dysfunction of heart, liver, lung or kidney);
4. high risk of thrombosis;
5. recurrent AEH;
6. endometrial cancer;
7. other malignancy history.

Data will be shared with other researchers without patients' personal information after all the findings being published.