Inclusion Criteria:

          -  Patients with histologically documented local-regional recurrent squamous cell
             carcinoma of the head and neck, or second primary squamous cell carcinoma of the head
             and neck

          -  Patients must be willing to undergo research biopsy for tissue collection at baseline
             and at disease progression

          -  Previous receipt of at least 30 Gy of radiation for head and neck squamous cell cancer
             (HNSCC) with overlapping fields

          -  Not eligible or poor candidate or patient refusal of surgery for recurrence

          -  Evaluable disease apparent on imaging (MRI or computed tomography [CT])

          -  1 to 3 sites of recurrence (< 60 cm^3 per site, total volume < 100 cm^3)

          -  Eastern Cooperative Oncology Group (ECOG) = 0, 1, or 2

          -  White blood count (WBC) >= 2000/L

          -  Absolute neutrophil count (ANC) >= 1,500 cells/mm^3

          -  Platelets >= 100,000 cells/mm^3

          -  Hemoglobin >= 9.0 g/dl; Note: The use of transfusion or other intervention to achieve
             hemoglobin (Hgb) >= 9.0 g/dl is acceptable

          -  Serum creatinine =< 1.5 mg/dl or creatinine clearance (CC) >= 50 ml/min determined by
             24-hour collection or estimated by Cockcroft-Gault formula

          -  Total bilirubin =< 1.5 x upper limit of normal (ULN) (except patients with Gilbert
             syndrome who can have total bilirubin < 3.0 mg/dL)

          -  Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) < 3 x the upper
             limit of normal

          -  Negative serum pregnancy test for women of childbearing potential and confirmation
             within 24 hours of first dose of study drug

        Exclusion Criteria:

          -  Presence of distant metastases

          -  Less than six-month disease free interval from end of prior radiotherapy to the head
             and neck

          -  Prior receipt of anti-PD-1/L1

          -  Patients who are pregnant or breast feeding

          -  Clinically significant uncontrolled major cardiac, respiratory, renal, hepatic,
             gastrointestinal or hematologic disease but not limited to: symptomatic congestive
             heart failure, unstable angina, or cardiac dysrhythmia not controlled by pacer device;
             myocardial infarction within 3 months of registration

          -  Active autoimmune disorder or immunosuppression (including human immunodeficiency
             virus [HIV], but excluding endocrine abnormalities that are controlled with
             replacement medications)

          -  Active viral hepatitis

          -  Steroid therapy of greater than prednisone 10 mgs a day or equivalent

          -  Prior history of invasive non-head and neck cancer within two years, with the
             exception of screen detected prostate cancer treated with observation only, basal cell
             and squamous cell carcinoma of the skin, and micro-invasive resected cervical
             carcinoma