Next-gen Flow Cytometry to Find Immune Profiles, Treatment Response, and Toxicity Markers in Skin Cancer Patients Treated With Cemiplimab.

\- Inclusion criteria At least 18 years old Hepatic function: 1. Total bilirubin ≤1.5x upper limit of normal (ULN) (or ≤3x ULN, if liver metastases). 2. Patients with Gilbert's Disease and total bilirubin up to 3x ULN may be eligible after communication with and approval from the medical monitor 3. Transaminases ≤3x ULN (or ≤5x ULN, if liver metastases) 4. Alkaline phosphatase (ALP) ≤2.5x ULN (or ≤5x ULN, if liver or bone metastases) Renal function: Serum creatinine ≤2x ULN or estimated creatinine clearance \>35 mL/min (according the method of Cockcroft and Gault) Creatine phosphokinase (CPK) (also known as CK \[creatine kinase\]) elevation ≤ grade 2 Bone marrow function: a. Hemoglobin ≥9.0 g/dL b. Absolute neutrophil count (ANC) ≥1.5 x 109/L c. Platelet count ≥75 x 109/L Anticipated life expectancy \>12 weeks \- Exclusion criteria: 1. \- Patient who refuses to participate in the study. 2. Being unsuitable for cemiplimab treatment 3. Ongoing or recent (within 5 years) evidence of significant autoimmune disease that required treatment with systemic immunosuppressive treatments, which may suggest risk for immune-related adverse events (irAEs). The following are not exclusionary: vitiligo, childhood asthma that has resolved, type 1 diabetes, residual hypothyroidism requiring only hormone replacement, or psoriasis that does not require systemic treatment. 4. Untreated brain metastasis(es) that may be considered active. a. Note in clarification: Patients with previously treated brain metastases may participate provided that the lesion(s) is (are) stable (without evidence of progression for at least 6 weeks on imaging obtained in the screening period), and there is no evidence of new or enlarging brain metastases, and the patients do not require any immunosuppressive doses of systemic corticosteroids for management of brain metastasis(es) within 28 days of the first dose of REGN2810cemiplimab. 5. Immunosuppressive corticosteroid doses (\>10 mg prednisone daily or equivalent) within 4 weeks prior to the first dose of REGN2810cemiplimab a. Note in clarification: Patients who require brief courses of steroids (eg, as prophylaxis for imaging studies due to hypersensitivity to contrast agents) are not excluded 6. Active infection requiring therapy, including positive tests for human immunodeficiency virus (HIV)-1 or HIV-2 serum antibody, hepatitis B virus (HBV), or hepatitis C virus (HCV) 7. History of pneumonitis within the last 5 years 8. Any anticancer treatment other than radiation therapy (chemotherapy, targeted systemic therapy, imiquimod, photodynamic therapy), investigational or standard of care, within 30 days of the initial administration of REGN2810 cemiplimab or planned to occur during the study period 9. History of documented allergic reactions or acute hypersensitivity reaction attributed to antibody treatments 10. Patients with allergy or hypersensitivity to REGN2810 cemiplimab or to any of the excipients must be excluded. 11. Patients with a history of solid organ transplant (patients with prior corneal transplants may be allowed to enroll after discussion with and approval from the medical monitor) 12. Breastfeeding 13. Positive serum pregnancy test (a false positive pregnancy test, if demonstrated by serial measurements and negative ultrasound, will not be exclusionary, upon communication with and approval from the medical monitor) 14. Receipt of live vaccines (including attenuated) within 30 days of first study treatment 15. Women of childbearing potential (WOCBP)\*, or sexually active men, who are unwilling to practice highly effective contraception prior to the initial dose/start of the first treatment prior to the start of the first treatment, during the study, and for at least 6 months after the last dose. Optional criteria, depending on the therapy being investigated: 16. Prior treatment with an agent that blocks the PD-1/PD-L1 pathway (If a study is addressing prior unsuccessful treatment with PD-1/PD-L1 inhibitor, it is suggested to exclude patients who had suffered from ≥grade 3 irAE during previous treatment) 17. Prior treatment with other systemic immune-modulating agents within fewer than 28 days prior to the first dose of REGN2810cemiplimab. Examples of immune-modulating agents include therapeutic vaccines, cytokine treatments, or agents that target cytotoxic T-lymphocyte antigen 4 (CTLA-4), 4-1BB (CD137), or OX-40. 1. Note in clarification: Prior treatment with imiquimod or other topical or intralesional immune modulators will not be exclusionary