Patients with biopsy proven locoregional recurrence or second primary SCCHN which is
        unresectable or the patient is unwilling to undergo resection. Determination of
        unresectability will be based on multidisciplinary review of each case.

        Inclusion Criteria:

          1. Have received only prior radiation treatment course. Prior radiation course must have
             been with curative intent.

          2. At least 6 months since completion of radiation

          3. Based on prior radiation records, have had most of the tumor volume (>50%) previously
             radiated at doses > 45 Gy without exceeding spinal cord tolerance (combining previous
             and future radiation dose to spinal cord of < 50 Gy).

          4. Be willing to undergo percutaneous endoscopic gastrostomy (PEG) placement, if
             necessary.

          5. Have at least one measurable area of disease based on RECIST 1.1 within the previously
             radiated field.

          6. Have provided adequate tissue for PD-L1 analysis either from an archival tissue sample
             or fresh biopsy done to confirm recurrence/second primary. Archival tissue sample can
             only be used if done within 3 months of enrollment on the clinical trial.

          7. Performance status of 0 or 1 on the ECOG Performance Scale.

          8. Life expectancy greater than 12 weeks

          9. Adequate organ function as defined by the protocol

        Exclusion Criteria:

          1. Presence of distant metastatic disease.

          2. Is currently participating in or has participated in a study of an investigational
             agent or used an investigational device within 4 weeks of the first dose of treatment.

          3. 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.

          4. Has had a prior monoclonal antibody, chemotherapy, or targeted small molecule therapy
             within 4 weeks prior to study Day 1 or who has not recovered from adverse events due
             to agents administered more than 4 weeks earlier.

          5. History of other malignancy within 5 years with the exception of prior Squamous cell
             carcinoma of the head and neck, adequately treated basal cell or squamous cell skin
             cancer, or carcinoma of the cervix.

          6. Has an active autoimmune disease

          7. Has evidence of interstitial lung disease or active, non-infectious pneumonitis.

          8. Has an active infection requiring systemic therapy

          9. Has received prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or
             anti-Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) antibody (including
             ipilimumab or any other antibody or drug specifically targeting T-cell co-stimulation
             or checkpoint pathways).

         10. Has a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies).

         11. Has known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA
             [qualitative] is detected).

         12. Has received a live vaccine within 30 days prior to the first dose of trial treatment

         13. Is pregnant or breastfeeding, or expecting to conceive or father children within the
             projected duration of the trial.