ctDNA in Cutaneous Squamous Cell Carcinoma

Post-Operative Cohort Inclusion Criteria: * Patients with surgically resectable primary CSCC with PNI (\>0.1mm caliber nerve) or at least 2 high-risk features defined as size \> 2cm, recurrent CSCC, LVI, immunosuppressed, poorly differentiated, and/or invasion \>6mm/beyond subcutaneous fat; * Patients with surgically resectable regional metastases not receiving neoadjuvant therapy Exclusion Criteria: * Patients with Cutaneous Squamous Cell Carcinoma not amenable to surgical resection * Patients receiving or undergoing systemic therapies. Neoadjuvant Cohort Inclusion Criteria: * Patients with resectable AJCC (8th ed) Stage II, III or IV(M0) CSCC treated with neoadjuvant immunotherapy as part of standard care. Exclusion Criteria: * Patients ineligible for neoadjuvant treatment. Definitive Immunotherapy Cohort Inclusion Criteria: * Patients with unresectable locally advanced or metastatic CSCC, AJCC (8th ed) Stage II, III, or IV), receiving immunotherapy as part of standard of care. Exclusion Criteria: * Patients undergoing systemic therapies outside the standard of care or enrolled in conflicting clinical trials.