Inclusion Criteria:

          1. Male/female participants who are at least 18 years of age on the day of signing
             informed consent with histologically confirmed diagnosis of high-risk localized or
             locooregional cSCC as defined below may be enrolled in this study.

             a. NOTE: Patients are eligible for this trial either at initial presentation for cSCC
             with locally advanced and/or concurrent regional nodal metastasis; or at the time of
             recurrence with locally advanced and/or concurrent regional nodal metastasis assuming
             following criteria are met per the cSCC-specific AJCC UICC 8th edition staging
             classification

             i. T2 and Nx and M0 (tumor >2 cm and ≤4 cm in greatest dimension) OR;

             ii. T3 and Nx and M0 (tumor >4 cm or minor bone erosion or perineural invasion or deep
             invasion) OR;

        1.Deep invasion is defined as invasion beyond the subcutaneous fat or >6 mm (as measured
        from the granular layer of adjacent normal epidermis to the base of the tumor).

        2.Perineural invasion is defined as tumor cells within the nerve sheath of a nerve lying
        deeper than the dermis or measuring 0.1 mm or larger in caliber, or presenting with
        clinical or radiographic involvement of named nerves without skull base invasion or
        transgression.

        iii. T4 and Nx and M0 (tumor with gross cortical bone/marrow, skull base invasion and/or
        skull base foramen invasion if deemed surgically resectable) OR;

        iv. Tx and N1-3 and M0 (if deemed surgically resectable) OR;

        b. NOTE:

        i. If T2, tumors must possess ≥2 NCCN/BWH clinical or pathologic risk factor(s) as stated
        below.

        ii. NCCN/BWH clinical risk factors:

          1. Tumors ≥20 mm on trunk or extremities (excluding pretibia, hands, feet, nail units,
             and ankles).

          2. Tumors ≥10 mm on cheeks, forehead, scalp, neck, or pretibial areas.

        iii. NCCN/BWH pathologic risk factors:

          1. Poorly defined borders.

          2. Recurrent tumors.

          3. Neurologic symptoms to suggest perineural invasion.

          4. High-risk histologic subtypes including: poorly differentiated tumor, acantholytic
             (adenoid), adenosquamous, desmoplastic, or metaplastic (carcinosarcomatous) subtypes
             (as stated in the pathology report or written documentation by Mohs surgeon).

          5. Histopathologically documented perineural, lymphatic, or vascular involvement (as
             stated in the pathology report or written documentation by Mohs surgeon).

             c. NOTE: Tumors of any size on the "mask areas" of the face [central face, eyelids,
             eyebrows, periorbital nose, lips (cutaneous and vermilion), chin, mandible,
             preauricular and postauricular skin/sulci, temple, ear, genitalia, hands, and feet]
             are not eligible.

             d. NOTE: Patients with tumors that arise in the setting of chronic inflammation
             (Marjolin's ulcer) such as chronic wounds and/or scars are excluded.

             e. NOTE: Determination of surgical resectability must be made before enrollment by the
             treating surgical oncologist (or ENT surgeon or equivalent).

        2. Male participants: A male participant must agree to use a contraception during the
        treatment period and for at least 120 days after the last dose of study treatment and
        refrain from donating sperm during this period.

        3. Female participants:

        A female participant is eligible to participate if she is not pregnant, not breastfeeding,
        and at least one of the following conditions applies:

          1. Not a woman of childbearing potential (WOCBP)

             OR

          2. A WOCBP who agrees to follow the contraceptive guidance during the treatment period
             and for at least 120 days after the last dose of study treatment.

             4. The participant (or legally acceptable representative if applicable) provides
             written informed consent for the trial.

             5. Have at least a single site of measurable disease based on RECIST 1.1. Lesions
             situated in a previously irradiated area are considered measurable if progression has
             been demonstrated in such lesions.

             6. Willing to undergo pre-treatment biopsies.

        a. Prior archival tumor tissue sample are not permitted.

        b. Minimum tissue requirements: core (16G or 18G, 6 cores; preferred), punch or excisional
        biopsy of a tumor lesion that has not been previously irradiated.

        7. Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.

          1. ECOG evaluation should be performed at Screening and repeated on Cycle 1 Day 1.

             8. Have adequate organ function, per protocol criteria

        Exclusion Criteria:

          1. Diagnosis of immunodeficiency, immunosuppression and/or is receiving systemic steroid
             therapy or any other form of immunosuppressive therapy within 7 days prior to the
             first dose of trial treatment.

          2. Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti PD L2 agent or with
             an agent directed to another stimulatory or co-inhibitory T-cell receptor (eg, CTLA-4,
             OX 40, CD137).

          3. Prior chemotherapy, targeted small molecule 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.

          4. Has received prior radiotherapy within 2 weeks of start of study intervention.
             Participants must have recovered from all radiation-related toxicities, not require
             corticosteroids, and not have had radiation pneumonitis. A 2-week washout is permitted
             for palliative radiation (≤2 weeks of radiotherapy) to non-CNS disease.

          5. Is currently participating in or has participated in a study of an investigational
             agent or has used an investigational device within 4 weeks prior to the first dose of
             study intervention.

          6. A WOCBP who has a positive urine pregnancy test at Screening. If the urine test is
             positive or cannot be confirmed as negative, a serum pregnancy test will be required.

          7. Has received a live vaccine within 30 days prior to the first dose of study drug.

               1. Examples of live vaccines include, but are not limited to, the following:
                  measles, mumps, rubella, varicella/zoster (chicken pox), yellow fever, rabies,
                  Bacillus Calmette-Guérin (BCG), and typhoid vaccine.

               2. Seasonal influenza vaccines for injection are generally killed virus vaccines and
                  are allowed; however, intranasal influenza vaccines (eg, FluMist®) are live
                  attenuated vaccines and are not allowed.

          8. Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy
             (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of
             immunosuppressive therapy within 14 days prior to the first dose of study drug.

          9. 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).

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

         10. Concurrent non-hematologic malignancy other than cSCC within 3 years of data of first
             planned dose of therapy except for tumors with a negligible risk of metastasis and/or
             death as defined below:

               1. Adequately treated non-invasive malignancies including but not limited to
                  melanoma in situ (MIS), BCC, CIS of cervix, or DCIS of breast may be enrolled.

               2. Low-risk early stage prostate adenocarcinoma (T1-T2a N0 M0 and Gleason score ≤6
                  and PSA ≤10 ng/mL) for which the management plan is active surveillance, or
                  prostate adenocarcinoma with biochemical-only recurrence with documented PSA
                  doubling time of > 12 months for which the management plan is active surveillance
                  may be enrolled.

               3. Indolent hematologic malignancies for which the management plan is active
                  surveillance including but not limited to CLL/indolent lymphoma may be enrolled.

             i. Patients with high-risk hematologic malignancies (CML, ALL, AML, Hodgkin's or non-
             Hodgkin's lymphoma) are excluded even if the management plan is active surveillance.

         11. Has known active CNS metastases and/or carcinomatous meningitis.

             a. Note: Participants with previously treated brain metastases may participate
             provided they are radiologically stable, i.e. without evidence of progression for at
             least 4 weeks by repeat imaging (note that the repeat imaging should be performed
             during Screening), clinically stable and without requirement of steroid treatment for
             at least 14 days prior to first dose of study intervention.

         12. Has severe hypersensitivity (≥Grade 3) to pembrolizumab and/or any of its excipients.

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

         14. Has an active infection requiring systemic therapy.

         15. Has a known history of Human Immunodeficiency Virus (HIV) infection.

         16. Has a known history of Hepatitis B (defined as Hepatitis B surface antigen [HBsAg]
             reactive) and/or known active Hepatitis C virus (defined as anti-HCV reactive)
             infection.

             a. Patients with treated Hepatitis B/C with no evidence of active infection may be
             enrolled.

         17. Has a known history of active TB (Bacillus Tuberculosis).

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

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

         20. Is pregnant or breastfeeding or expecting to conceive or father children within the
             projected duration of the study, starting with the Screening visit through 120 days
             after the last dose of trial treatment.

         21. Has had an allogenic tissue/solid organ transplant.