Inclusion Criteria:

   - Patients must have measurable stage III, measurable stage IVA, stage IVB (with or
   without measurable disease) or recurrent (with or without measurable disease)
   endometrial carcinoma

      - Histologic confirmation of the original primary tumor is required; patients with
      the following histologic epithelial cell types are eligible:

         - Endometrioid adenocarcinoma, serous adenocarcinoma, undifferentiated
         carcinoma, clear cell adenocarcinoma, mixed epithelial carcinoma,
         adenocarcinoma not otherwise specified (N.O.S.)

   - Measurable disease is defined by Response Evaluation Criteria in Solid Tumors (RECIST)
   (version 1.1); measurable disease is defined as at least one lesion that can be
   accurately measured in at least one dimension (longest diameter to be recorded); each
   lesion must be >= 10 mm when measured by computed tomography (CT), magnetic resonance
   imaging (MRI) or caliper measurement by clinical exam; or >= 20 mm when measured by
   chest x-ray; lymph nodes must be >= 15 mm in short axis when measured by CT or MRI

   - Patients must have a Gynecologic Oncology Group (GOG) performance status of 0, 1, or 2

   - Absolute neutrophil count (ANC) greater than or equal to 1,500/mcl

   - Platelets greater than or equal to 100,000/mcl

   - Creatinine less than 1.4 mg/dl

   - Bilirubin less than or equal to 1.5 x institutional/laboratory upper limit of normal
   (ULN)

   - Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) less than or equal
   to 3 x ULN

   - Alkaline phosphatase less than or equal to 2.5 x ULN

   - Patients must NOT have received prior chemotherapy or targeted therapy, including
   chemotherapy used for radiation sensitization for treatment of endometrial carcinoma

   - Patients may have received prior radiation therapy for treatment of endometrial
   carcinoma; prior radiation therapy may have included pelvic radiation therapy,
   extended field pelvic/para-aortic radiation therapy, and/or intravaginal
   brachytherapy; all radiation therapy must be completed at least 4 weeks prior to the
   first date of study therapy

   - Patients may have received prior hormonal therapy for treatment of endometrial
   carcinoma; all hormonal therapy must be discontinued at least one week prior to the
   first date of study therapy

   - Patients must be able to swallow and retain orally-administered medication

   - Patients must have signed an approved informed consent and authorization permitting
   release of personal health information; individuals with impaired decision-making
   capacity are not eligible to participate on the study

Exclusion Criteria:

   - Patients must NOT be taking metformin or have been on metformin in the past 6 months

   - Patients with a history of other invasive malignancies, with the exception of
   non-melanoma skin cancer are excluded if there is any evidence of other malignancy
   being present within the last three years

   - Uncontrolled intercurrent illness including, but not limited to, ongoing or active
   infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac
   arrhythmia, or psychiatric illness/social situations that would limit compliance with
   study requirements

   - Patients who are pregnant or nursing; if patients are of reproductive age and have not
   undergone hysterectomy, they must use an effective contraceptive method for the
   duration of this study

   - Any condition associated with increased risk of metformin-associated lactic acidosis;
   (e.g. congestive heart failure defined as New York Heart Association [NYHA] class III
   or IV functional status, history of acidosis of any type; habitual intake of 3 or more
   alcoholic beverages per day)