CD274 and skin squamous cell carcinoma: One of the first clinical evidence supporting the use of the anti-PD-1 immunotherapy for the treatment of advanced CSCC was provided by the CARSKIN trial, where first-line therapy with pembrolizumab in patients with unresectable CSCC demonstrated an objective response rate at week 15 of treatment (ORRW15) of 55% in PD-L1+ patients versus 17% in PD-L1- patients (41).