['erythroplakia', 'hyperplasia', 'oral cavity carcinoma', 'oral leukoplakia']
['metformin hydrochloride']

        Inclusion Criteria:

          -  Participants with oral leukoplakia or erythroplakia with mild, moderate, or severe
             histologic dysplasia, or hyperplasia not associated with mechanical factors such as
             ill-fitted dentures

          -  Measurable disease - minimum lesion size of 8 x 3 mm before initial biopsy

          -  Karnofsky performance status >= 70%

          -  Leukocytes >= 3,000/microliter

          -  Absolute neutrophil count >= 1,000/microliter

          -  Platelets >= 100,000/microliter

          -  Total bilirubin =< 1.5 × institutional upper limit of normal (ULN)

          -  Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase
             [SGOT])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT])
             =<1.5 × institutional ULN

          -  eGFR > 40 mL/min using the Cockcroft-Gault equation

          -  Life expectancy > 3 months

          -  Willing to use adequate contraception (barrier method, abstinence, subject has had a
             vasectomy or partner is using effective birth control or is postmenopausal) for the
             duration of study participation

          -  Ability to take oral medication

          -  Ability to understand and the willingness to sign a written informed consent document

        Exclusion Criteria:

          -  Patients with diabetes who are taking insulin or oral agents

          -  History of diabetic ketoacidosis

          -  Participants may not be receiving any other investigational agents within past 3
             months

          -  History of allergic reactions attributed to compounds of similar chemical composition
             to metformin or prior use of metformin within the last year

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

          -  Oral carcinoma in situ

          -  History of chronic alcohol use or abuse defined as any one of the following: a)
             average consumption of 3 or more alcohol containing beverages daily in the past 12
             months; b) consumption of 7 or more alcoholic beverages within a 24 hour (hr) period
             in the past 12 months

          -  Glycated hemoglobin (HbA1c) > 8%

          -  Pregnancy or nursing women

          -  Acute or chronic liver disease, evidence of hepatitis (infectious or autoimmune),
             cirrhosis or portal hypertension

          -  History of renal disease

          -  History of prior head and neck squamous cell carcinoma (HNSCC) unless curatively
             treated for >= 1 year

          -  Have received chemotherapy and/or radiation for any malignancy (excluding non-melanoma
             skin cancer and cancers confined to organs with removal as only treatment) in the past
             2 years; ongoing adjuvant hormonal therapy for breast cancer is allowed
      