Rapid Assessment of Tumor Thickness in Cutaneous Squamous Cell Carcinoma Using Ex Vivo Confocal Microscopy

<b>Objectives</b>: Ex vivo confocal laser scanning microscopy (EVCM) is a pioneering diagnostic method that enables fresh tissue samples to be analyzed directly during surgery. For the assessment of non-melanocytic skin cancer (NMSC), including cutaneous squamous cell carcinoma (cSCC), it provides a rapid addition to conventional histology. While previous studies have shown that EVCM reliably identifies the morphological features of cSCCs, quantitative criteria such as tumor thickness have not yet been systematically evaluated. This study investigated whether EVCM can be used to accurately and reproducibly measure the thickness of cSCCs, an important parameter for predicting metastatic risk. <b>Methods</b>: Eighty-two histologically verified cSCCs from different anatomical sites were assessed by the current gold standard of histopathology and EVCM. A statistical comparison of the confocal tumor thickness (CTT) and the histopathological tumor thickness (HTT) was then performed. In addition, it was analyzed how reliable EVCM was in the assignment of cSCCs to the correct tumor thickness category. <b>Results</b>: There was a very high agreement between both methods, evidenced by a Spearman correlation coefficient of 0.94 and a coefficient of determination of 0.859. Overall, 95.1% of the samples were correctly classified into the appropriate tumor thickness category using EVCM. Cohen's Kappa of 0.90 indicated almost perfect agreement between EVCM and histology. <b>Conclusions</b>: These findings demonstrate that EVCM is a precise and reliable method for determining tumor thickness and the corresponding category in cSCCs. It enables immediate intraoperative assessment of the metastatic risk and preliminary classification of low-risk tumors. Additional studies with larger patient cohorts are required to further validate these results and support clinical implementation.