EGF and skin squamous cell carcinoma: To date, a number of systemic therapies have been used to treat cSCC, including: chemotherapeutics (cisplatin (67–69), 5-fluorouracil [5-FU] (67, 68, 70, 71), bleomycin (67), and doxorubicin (69)), 13-cis-retinoic acid (13cRA (72)), immunotherapies (interferon-α2a [IFN-α] (72)), gefitinib (73) and cetuximab (74) (agents targeting epidermal growth factor [EGFR]), and more recently nivolumab (75) and cemiplimab (76) (PD-1 immune checkpoint inhibitors).