The purpose of the study is to see if the combination of radiation therapy and cemiplimab immunotherapy is an effective treatment for people with locally advanced, unresectable CSCC.

Inclusion Criteria:

• Biopsy proven cutaneous squamous cell carcinoma which is locally advanced

  • Mixed histology tumors that are predominantly squamous cell carcinoma are eligible
  • Locally advanced primary tumor is T3-T4 and/or N+ by AJCC and/or UICC 8th edition clinical criteria

• T3-T4 primary tumor characteristics noted below:

  • Non-eyelid tumor >4 cm in maximum dimension or with bone erosion or invasion, perineural invasion of nerve 0.1 mm or larger, or invasion beyond subcutaneous fat or >6 mm from granular layer of adjacent normal epidermis
  • Eyelid tumor >2 cm or invading adjacent ocular, orbital or facial structures

• ≥18 years old

• Unresectable or medically inoperable according to local multidisciplinary consensus for reasons such as:

  • Tumor or regional lymph node metastases that has recurred despite ≥2 prior surgical procedures, with another curative resection unlikely
  • Tumor or nodal disease with significant local invasion that precludes complete resection
  • Tumor or nodal disease in anatomically challenging area where surgery may result in significant disfigurement or dysfunction (amputation of nose, ear, eye, digit, limb, etc)
  • Medical contraindication to surgery
  • Patient refusal of surgery due to anticipate morbidity

• ECOG ≤2

• Adequate bone marrow and metabolic function (by blood tests)

  • Total bilirubin ≤1.5 x upper limit of normal
  • Aspirate aminotransferase (AST) ≤3 x upper limit of normal
  • Alanine aminotransferase (ALT) ≤3 x upper limit of normal
  • Alkaline phosphatase ≤2.5 x upper limit of normal
  • Serum creatinine ≤1.5 x upper limit of normal or estimated creatinine clearance >30 mL/min according to Cockcroft-Gault formula
  • Hemoglobin >9 g/dL
  • Absolute neutrophil count ≥1.5 x10^9/L
  • Platelet count ≥75 x10^9/L

• Able to provide informed consent

• Acceptable candidate for curative intent radiotherapy and Cemiplimab immunotherapy, in opinion of radiation and medical oncologist, respectively

• Life expectancy >18 months

Exclusion Criteria:

• Primary tumor originating on the mucosal (non-hair bearing) lip or nose, anogenital (penis, scrotum, vulva, perianal) area

• Iatrogenic immunosuppression (>prednisone 10 mg/day or equivalent within 14 days of initiation of treatment)

• Women of child bearing potential unwilling or unable to use effective contraception while receiving treatment with cemiplimab and for 4 months thereafter

• Distant metastases

• Clinically significant autoimmune disease that requires iatrogenic immunosuppression

  o For example, severe rheumatoid arthritis requiring disease modifying antirheumatic drugs, such as methotrexate

• Current or previous hematopoietic malignancy (leukemia, lymphoma)

• Prior allogeneic transplant of solid organ or bone marrow

• Concurrent malignancies with >10% risk of metastasis or death within 2 years

• Prior aPD1 immunotherapy or PI3Kδ inhibitor use

• Prior radiotherapy for the cutaneous squamous cell carcinoma requiring treatment

• Other ongoing cancer therapy

  o Adjuvant endocrine therapy is permitted for patients with prostate or breast cancer

• Uncontrolled HIV or infectious hepatitis (viral load detectable in patient with known infection)

• Pregnancy or breastfeeding

• Comorbid or diagnostic abnormalities within the last year that would interfere with interpretation of study results

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.