Inclusion Criteria:

          -  Histological evidence of oral intra-epithelial neoplasia within 12 months prior to
             enrollment; subjects with a history or clinical diagnosis suggestive of oral
             intra-epithelial neoplasia, or patients with a history of invasive oral cancer are
             eligible, but must have a confirmed histological diagnosis of oral intra-epithelial
             neoplasia before randomization; histological evidence of oral intraepithelial
             neoplasia on an invasive oral cancer resection specimen is acceptable; a visible,
             measurable, clinical lesion (such as leukoplakia and/or erythroplakia) is not
             required; only individuals with high risk profiles will be considered eligible for
             randomization; high risk profiles are defined as patients without a prior oral cancer
             and have loss of heterozygosity (LOH) at 3p14 and/or 9p21 plus at least at one
             additional chromosomal site (4q,8p,11p,13q, or 17p) or patients with a prior oral
             cancer history and have LOH at 3p14 and/or 9p21; all high risk patients must also meet
             the additional eligibility criteria

          -  Be willing and able to provide written informed consent

          -  Be greater than or equal to 18 years of age on day of signing informed consent for the
             trial

          -  Be willing to provide tissue from a newly obtained oral biopsy

          -  Have a performance status of 0-2 on the Eastern Cooperative Oncology Group (ECOG)
             performance scale

          -  Absolute neutrophil count >= 1,500/mcL

          -  Platelets >= 75,000/mcL

          -  Serum total bilirubin =< 1.5 X upper limit of normal (ULN) or direct bilirubin =< ULN
             for subjects with total bilirubin levels > 1.5 ULN

          -  Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase [SGOT]) and
             alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT]) =< 2.5 X
             ULN

          -  Female subject of childbearing potential should have a negative urine or serum
             pregnancy test < 72 hours prior to receiving the first dose of study medication; if
             the urine test is positive or cannot be confirmed as negative, a serum pregnancy test
             will be required

          -  Female subjects of childbearing potential should be willing to use 2 methods of birth
             control or be surgically sterile, or abstain from heterosexual activity for the course
             of study therapy through 120 days after the last dose of study medication; subjects of
             childbearing potential are those who have not been surgically sterilized or have not
             been free from menses > 1 year

          -  Male subjects should agree to use an adequate method of contraception starting with
             the first dose of study therapy through 120 days after the last dose of the study
             therapy

        Exclusion Criteria:

          -  Is currently participating and receiving study therapy with potential anti-neoplastic
             activity, or has participated in a study of an investigational agent and received
             study therapy with potential anti-neoplastic activity within 4 weeks of the first dose
             of treatment

          -  Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any
             other form of immunosuppressive therapy within 7 days prior to the first dose of trial
             treatment

          -  Has a known history of active TB (Bacillus tuberculosis)

          -  Hypersensitivity to pembrolizumab or any of its excipients

          -  Has had a prior anti-cancer monoclonal antibody (mAb) within 4 weeks prior to study
             day 1 or who has not recovered (i.e., =< grade 2 at baseline) from adverse events due
             to agents administered more than 4 weeks earlier

          -  Has had prior chemotherapy, targeted small molecule therapy, or radiation therapy
             within 2 weeks prior to study day 1 or who has not recovered (i.e., =< grade 2 or at
             baseline) from adverse events due to a previously administered agent; Note: If the
             subject received major surgery, they must have recovered adequately from the toxicity
             and/or complications from the intervention prior to starting therapy

          -  Has a known additional malignancy that is progressing or requires active treatment
             other than adjuvant hormonal therapy; exceptions include basal cell carcinoma of the
             skin or squamous cell carcinoma of the skin or in situ cervical cancer

          -  Has active autoimmune disease that has required systemic treatment in the past 2 years
             (i.e., with use of disease modifying agents, corticosteroids or immunosuppressive
             drugs); replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid
             replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a
             form of systemic treatment

          -  Has a known history of, or any evidence of active, non-infectious pneumonitis

          -  Has an active infection requiring systemic therapy

          -  Has a history or current evidence of any condition, therapy, or laboratory abnormality
             that might confound the results of the trial, interfere with the subject's
             participation for the full duration of the trial, or is not in the best interest of
             the subject to participate, in the opinion of the treating investigator

          -  Has known psychiatric or substance abuse disorders that would interfere with
             cooperation with the requirements of the trial

          -  Is pregnant, or breastfeeding, or expecting to conceive or father children within the
             projected duration of treatment with pembrolizumab, starting with the pre-screening or
             screening visit through 120 days after the last dose of trial treatment

          -  Has received prior therapy with anti-PD-1, anti-PD-L1, or anti-PD-L2 agent

          -  Has a history of human immunodeficiency virus (HIV) (HIV 1/2 antibodies)

          -  Has known active hepatitis B (e.g., hepatitis B surface antigen [HBsAg] reactive) or
             hepatitis C (e.g., hepatitis C virus [HCV] ribonucleic acid [RNA] [qualitative] is
             detected)

          -  Has received a live vaccine within 30 days of planned start of study therapy; Note:
             Seasonal influenza vaccines for injection are generally inactivated flu vaccines and
             are allowed; however intranasal influenza vaccines are live attenuated vaccines, and
             are not allowed