The purpose of the study is to investigate the effects of metformin in addition to the conventional progestin therapy in the fertility-sparing treatment of early stage endometrial cancer.

Inclusion Criteria:

• Endometrial cancer radiologic International Federation of Obstetrics and Gynecology (FIGO) stage IA patients
• Endometrioid endometrial cancer patients
• FIGO cellular differentiation grade 1 patients
• Patients who wish to preserve fertility
• Patients who understand that the recommended treatment of endometrial cancer is surgical treatment even in early stages, but still wish to preserve fertility and avoid surgical treatment
• Patients who have good performance status (Eastern Cooperation Oncology Group (ECOG) performance score equal to or greater than 3)
• Patients who are not contraindicated to the progestin therapy
• Patients who are not contraindicated to the use of metformin

Exclusion Criteria:

• Patients who have already received chemotherapeutic or radiotherapeutic treatments for endometrial cancer
• Patients whose disease is already advanced and not indicated for fertility-sparing treatment
• Patients whose tumor cellular differentiation grade is greater than FIGO grade 1