Advanced cutaneous squamous cell carcinoma (cSCC) encompasses unresectable and metastatic disease. Although immune checkpoint inhibition has been approved for this entity recently, a considerable proportion of cases is associated with significant morbidity and mortality. Clinical, histopathological, and radiological criteria are used for current diagnostics, classification, and therapeutic decision-making. The identification of complex molecular biomarkers to accurately stratify patients is a not yet accomplished requirement to further shift current diagnostics and care to a personalized precision medicine. This article highlights new insights into the mutational profile of cSCC, summarizes current diagnostic and therapeutic standards, and discusses emerging diagnostic approaches with emphasis on liquid biopsy and tumor tissue-based analyses.

Immune checkpoint inhibition (ICI) has yielded remarkable results in prolonging survival of metastatic melanoma patients but only a subset of individuals treated respond to therapy. Success of ICI treatment appears to depend on the number of tumor-infiltrating effector T-cells, which are known to be influenced by activated eosinophils. To verify the co-occurrence of activated eosinophils and T-cells in melanoma, immunofluorescence was performed in 285 primary or metastatic tumor tissue specimens from 118 patients. Moreover, eosinophil counts and activity markers such as eosinophil cationic protein (ECP) and eosinophil peroxidase (EPX) were measured in the serum before therapy start and before the 4th infusion of ICI in 45 metastatic unresected melanoma patients. We observed a positive correlation between increased tumor-infiltrating eosinophils and T-cells associated with delayed melanoma progression. High baseline levels of eosinophil count, serum ECP and EPX were linked to prolonged progression-free survival in metastatic melanoma. Our data provide first indications that activated eosinophils are related to the T-cell-inflamed tumor microenvironment and could be considered as potential future prognostic biomarkers in melanoma.

Cutaneous squamous cell carcinoma (CSCC) is the most frequent post‐transplant tumour entity resulting from immunosuppression treatment that is needed to prevent organ rejection. Solid organ transplant (SOT) recipients are at higher risk for CSCC and vulnerable for aggressive disease or a fatal course. Here, we report on a case of post‐kidney transplant metastatic CSCC, demonstrating efficacy of cemiplimab in achieving complete remission after previous disease progression under cetuximab treatment. Unfortunately, the patient developed severe pneumonia, which was only later diagnosed as cemiplimab‐associated pneumonitis. Due to a rapidly evolving septic condition, intensive care treatment was required and resulted in a fatal outcome. The patient's transplant remained intact, yet first‐line treatment of advanced CSCC, such as with cemiplimab, should be weighed critically in SOT recipients, as transplant rejection may occur. However, the present case underlines the feasibility of cemiplimab as a second‐line treatment option in this patient collective.