Inclusion Criteria:

          -  Histologic diagnosis of cutaneous squamous cell carcinoma of the head and neck that
             has been resected with no evidence of gross residual disease (margin positivity is
             acceptable)

          -  Patients must have undergone resection of the disease and demonstrate high risk
             pathologic features including:

               -  T4

               -  Node positive disease

               -  T2/T3N0 disease with any 1 additional feature, including:

                    -  Recurrent Disease

                    -  Perineural invasion

                    -  Lymphovascular space invasion

                    -  Poorly differentiated histology

                    -  Positive Margins

                    -  Satellitosis or in-transit metastases

          -  Patients are required to have computerized tomography (CT) neck and chest or positron
             emission tomography/computerized tomography (PET/CT) and have no documented evidence
             of distant metastases

          -  Patients must not have a history of the following immunosuppressive conditions: bone
             marrow transplantation, lymphoid malignancies, or organ transplants and/or chronic
             rheumatic conditions that require active immunosuppressive therapy.

          -  Patients may not have had prior therapy with a checkpoint inhibitor (e.g.
             anti-CTLA-4, anti-PD-1 or anti-PD-L1 therapy)

          -  Patients may not have had prior radiotherapy (>30Gy) to the area requiring treatment
             that would result in any overlap of tissue in both fields

          -  Patients may have received chemotherapy or radiation for a previous, curatively
             treated malignancy provided at least 2 years have elapsed and there is no current
             evidence of disease (patients with previous or concurrent additional skin cancers are
             eligible)

          -  Eastern Cooperative Oncology Group (ECOG) Performance Status 0-1

          -  Female subject of childbearing potential should have a negative urine or serum
             pregnancy within 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 the study 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 for > 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 study
             therapy.

          -  Patients must have adequate laboratory values

               -  Absolute neutrophil count ≥ 1,500/mcL

               -  Platelets ≥ 100,00/mcL

               -  Hemoglobin ≥ 9g/dL or ≥5.6mmol/L without transfusion

               -  Serum creatinine ≤ 1.5 times upper limit of normal (ULN) or measured creatinine
                  clearance ≥60mL/min for subject with creatinine levels >1.5 times institutional
                  ULN

               -  Serum bilirubin ≤ 1.5 times ULN or direct bilirubin ≤ ULN for subjects with
                  total bilirubin levels > 1.5 ULN

               -  Aspartate aminotransferase (AST (SGOT)) and alanine aminotransferase (ALT
                  (SPGT)) ≤ 2.5 times ULN or ≤ 5 times ULN for subjects with liver metastases

               -  Albumin ≥ 2.5mg/dL

               -  International Normalized Ratio (INR) or Prothrombin Time (PT) ≤1.5 times ULN
                  unless subject is receiving anticoagulant therapy as long as PT is within
                  therapeutic range of intended use of anticoagulants. Activated Partial
                  Thromboplastin Time (aPTT) ≤1.5 times ULN unless subject is receiving
                  anticoagulant therapy as long as PT or aPTT is within therapeutic range of
                  intended use of anticoagulants

        Exclusion Criteria:

          -  Is currently participating and receiving study therapy or has participated in a study
             of an investigational agent and received study therapy or used an investigational
             device within 4 weeks of the first dose of treatment.

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

          -  Hypersensitivity to pembrolizumab.

          -  Has a history of the following immunosuppressive conditions: bone marrow
             transplantation, lymphoid malignancies, or organ transplants and/or chronic rheumatic
             conditions that require active immunosuppressive therapy

          -  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 1 or at baseline) from adverse events due
             to agents administered more than 4 weeks earlier.

          -  Has had prior chemotherapy, targeted small molecule therapy, or radiotherapy within 2
             weeks prior to study Day 1 or who has not recovered (i.e. ≤ Grade 1 or at baseline)
             from adverse events due to a previously administered agent.

          -  Has a known additional malignancy that is progressing or requires active treatment.
             Exceptions include basal cell carcinoma of the skin or a separate primary squamous
             cell carcinoma of the skin.

          -  Has metastatic disease.

          -  Has 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 the trial, starting with the pre-screening or screening visit
             through 120 days after the last dose of trial treatment.

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

          -  Has known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA is
             detected).

          -  Has received a live vaccine within 30 days of planned start of study therapy.