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Background: Cutaneous squamous cell carcinoma (cSCC) is the second most frequent non-melanoma skin cancer. Treatment options for inoperable advanced cSCC cases are limited. The efficacy of anti-programmed cell death-1 (PD-1) monoclonal antibodies (mAb) has been reported recently in some patients with cSCC. Objectives: To evaluate the efficacy of anti-PD-1 mAb in a case series of inoperable advanced cSCC and to analyse the efficacy of concurrent radiotherapy. Materials and Methods: We retrospectively analysed the files of all patients with advanced inoperable cSCC treated with anti-PD-1 mAb and concurrent radiotherapy outside clinical trials in our skin cancer centre before December 31, 2017. Results: A total of four patients with locally or regionally advanced cSCC were identified. All patients received pembrolizumab at 2 mg/kg every three weeks and concurrent radiotherapy. Two patients who received pembrolizumab as first-line therapy with concurrent radiotherapy (one with skull and leptomeningeal invasion and one with rapidly progressing regional cSCC) had a complete response, allowing treatment discontinuation, without recurrence after a median of 11 months off treatment. All other patients experienced progressive disease. The median progression-free survival and overall survival were 14.4 and 15.6 months, respectively. No toxicity was observed. Conclusion: There appears to be a place for pembrolizumab as first-line treatment for unresectable or advanced cSCC. Further studies are needed to evaluate concomitant radiotherapy with anti-PD1 antibodies.