Inclusion Criteria:

          -  All subjects must have cutaneous squamous cell carcinoma that is not curable by
             surgery or radiation; both locally advanced and metastatic squamous cell carcinoma
             will be included.

          -  Be willing and able to provide written informed consent/assent for the trial.

          -  Have measurable disease based on Response Evaluation Criteria in Solid Tumors (RECIST)
             1.1.

          -  Be willing to provide tissue from a newly obtained core or excisional biopsy of a
             tumor lesion. Newly-obtained is defined as a specimen obtained up to 6 weeks (42 days)
             prior to initiation of treatment on day 1. Subjects for whom newly-obtained samples
             cannot be provided (e.g. inaccessible or subject safety concern) may submit an
             archived specimen only upon agreement from the sponsor.

          -  Be willing to undergo normal skin biopsy prior to initiation of treatment and after
             treatment.

          -  Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG)
             performance scale.

          -  Absolute neutrophil count (ANC) ≥ 1,500/microliter (mcL)

          -  Platelets ≥ 100,000/mcL

          -  Hemoglobin ≥ 9 g/dL or ≥ 5.6 mmol/L without transfusion or erythropoietin (EPO)
             dependency (within 7 days of assessment)

          -  Serum creatinine ≤ 1.5 X upper limit of normal (ULN) OR measured or calculated
             creatinine clearance (glomerular filtration rate [GFR] can also be used in place of
             creatinine or creatinine clearance [CrCl]) ≥ 60 mL/min for subject with creatinine
             levels > 1.5 X institutional ULN

          -  Serum total bilirubin ≤ 1.5 X 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 OR ≤ 5 X ULN for subjects with liver metastases

          -  Albumin ≥ 2.5 mg/dL

          -  International normalized ratio (INR) or prothrombin time (PT) ≤ 1.5 X ULN unless
             subject is receiving anticoagulant therapy as long as PT or partial thromboplastin
             time (PTT) is within therapeutic range of intended use of anticoagulants.

          -  Activated partial thromboplastin rime (aPTT) ≤ 1.5 X ULN unless subject is receiving
             anticoagulant therapy as long as PT or PTT is within therapeutic range of intended use
             of anticoagulants.

          -  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.

        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 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, patients with human immunodeficiency virus (HIV) adequately controlled on
             antiretrovirals (undetectable viral load) and patients with chronic lymphocytic
             leukemia (CLL) not requiring systemic treatment will be included; in addition,
             steroids for physiologic replacement will be allowed (must be equal to or less than
             10mg of prednisone/day).

          -  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 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 radiation therapy
             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.

               -  Note: subjects with ≤ grade 2 neuropathy are an exception to this criterion and
                  may qualify for the study.

               -  Note: if 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;
             exceptions include basal cell carcinoma of the skin that has undergone potentially
             curative therapy or in situ cervical cancer. Asymptomatic CLL, not requiring
             intervention will be included as long as patients meet routine laboratory parameters
             of the study as outlined above. In addition, patients who have undergone curative bone
             marrow transplant and currently not requiring immunosuppression, will be allowed on
             study.

          -  Has known active central nervous system (CNS) metastases and/or carcinomatous
             meningitis; subjects with previously treated brain metastases may participate provided
             they are stable (without evidence of progression by imaging for at least four weeks
             prior to the first dose of trial treatment and any neurologic symptoms have returned
             to baseline), have no evidence of new or enlarging brain metastases, and are not using
             steroids for at least 7 days prior to trial treatment; this exception does not include
             carcinomatous meningitis which is excluded regardless of clinical stability.

          -  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 (eg., thyroxine, insulin, or physiologic corticosteroid
             replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a
             form of systemic treatment.

          -  Has a history of (non-infectious) pneumonitis that required steroids or current
             pneumonitis.

          -  Has an active infection requiring systemic therapy; exception HIV on antiretrovirals
             with negative viral load.

          -  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-programmed cell death (PD)-1, anti- programmed
             cell death 1 ligand (PD-L)1, or anti-PD-L2 agent.

          -  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. Seasonal
             influenza vaccines for injection are generally inactivated flu vaccines and are
             allowed; however intranasal influenza vaccines (e.g., Flu-Mist) are live attenuated
             vaccines, and are not allowed.

          -  cSCC that is curable via radiation or surgery; palliative radiation is allowed as long
             as measurable disease outside radiation field is present for study.