Catharina Margrethe Lerche

PD‐1 checkpoint inhibitors are used as systemic immunotherapy for locally advanced and metastatic cutaneous squamous cell carcinoma (SCC); however, improved treatment efficacy is urgently needed. In this study, we aimed to investigate the effect of combining systemic anti‐PD‐1 treatment with adjuvant ablative fractional laser (AFL) in a spontaneous SCC mouse model. Tumours induced by ultraviolet radiation in the strain C3.Cg‐ Hr hr /TifBomTac were divided into four groups: anti‐PD‐1‐antibody+AFL ( n = 33), AFL alone ( n = 22) anti‐PD‐1‐antibody alone ( n = 31) and untreated controls ( n = 46). AFL was given at Day 0 (100 mJ/mb, 5% density), while anti‐PD‐1‐antibody (ip, 200 μg) at Days 0, 2, 4, 6 and 8. Response to treatment was evaluated by tumour growth, survival time and by dividing response to treatment into complete responders (clinically cleared tumours), partial responders (reduced tumour growth rate compared to untreated controls) and non‐responders (no decrease in tumour growth rate compared to untreated controls). The strongest tumour response was observed following the combination of systemic anti‐PD‐1 treatment combined with laser exposure, resulting in the highest percentage of complete responders (24%) compared with untreated controls (0%, p < 0.01), AFL monotherapy (13%, p > 0.05) and anti‐PD‐1‐antibody monotherapy (3%, p > 0.05). Moreover, all three treatment interventions demonstrated significantly reduced tumour growth rates compared with untreated controls ( p < 0.01), and the mice had significantly longer survival times ( p < 0.01). In conclusion, the combination treatment revealed an improved treatment effect that significantly enhanced the complete tumour clearance not observed with the monotherapies, indicating a possible additive effect of anti‐PD‐1 with adjuvant AFL in treatment of SCC.